Treatment for bovine Escherichia coli mastitis - an evidence-based approach

The occurrence of Aerococcus urinaeequi and non-aureus staphylococci in raw milk negatively correlates with Escherichia coli clinical mastitis

Escherichia coli is a common environmental pathogen associated with clinical mastitis (CM) in dairy cattle. There is an interest in optimizing the udder microbiome to increase the resistance of dairy cattle to E. coli CM; however, the details of which members of the healthy udder microbiome may play a role in antagonizing E. coli are unknown. In this study, we characterized the bacterial community composition in raw milk collected from quarters of lactating Holstein dairy cows that developed E. coli CM during lactation, including milk from both healthy and diseased quarters (n = 1,172). The milk microbiome from infected quarters was compared before, during, and after CM. A combination of 16S rRNA gene amplicon and metagenomic sequencing was used generate data sets with a high level of both depth and breadth. The microbial diversity present in raw milk significantly decreased in quarters experiencing E. coli CM, indicating that E. coli displaces other members of the microbiome. However, the diversity recovered very rapidly after infection. Two genera, Staphylococcus and Aerococcus, and the family Oscillospiraceae were significantly more abundant in healthy quarters with low inflammation. Species of these genera, Staphylococcus auricularis, Staphylococcus haemolyticus, and Aerocussus urinaeequi, were identified by metagenomics. Thus, these species are of interest for optimizing the microbiome to discourage E. coli colonization without triggering inflammation.IMPORTANCEIn this study, we show that E. coli outcompetes and displaces several members of the udder microbiome during CM, but that microbial diversity recovers post-infection. In milk from quarters which remained healthy, the community composition was often highly dominated by S. auricularis, S. haemolyticus, A. urinaeequi, and S. marcescens without increases in somatic cell count (SCC). Community dominance by these organisms, without inflammation, could indicate that these species might have potential as prophylactic probiotics which could contribute to colonization resistance and prevent future instances of E. coli CM.

Genes associated with fitness and disease severity in the pan-genome of mastitis-associated Escherichia coli

Introduction

Bovine mastitis caused by Escherichia coli compromises animal health and inflicts substantial product losses in dairy farming. It may manifest as subclinical through severe acute disease and can be transient or persistent in nature. Little is known about bacterial factors that impact clinical outcomes or allow some strains to outcompete others in the mammary gland (MG) environment. Mastitis-associated E. coli (MAEC) may have distinctive characteristics which may contribute to the varied nature of the disease. Given their high levels of intraspecies genetic variability, virulence factors of commonly used MAEC model strains may not be relevant to all members of this group.

Methods

In this study, we sequenced the genomes of 96 MAEC strains isolated from cattle with clinical mastitis (CM). We utilized clinical severity data to perform genome-wide association studies to identify accessory genes associated with strains isolated from mild or severe CM, or with high or low competitive fitness during in vivo competition assays. Genes associated with mastitis pathogens or commensal strains isolated from bovine sources were also identified.

Results

A type-2 secretion system (T2SS) and a chitinase (ChiA) exported by this system were strongly associated with pathogenic isolates compared with commensal strains. Deletion of chiA from MAEC isolates decreased their adherence to cultured bovine mammary epithelial cells.

Discussion

The increased fitness associated with strains possessing this gene may be due to better attachment in the MG. Overall, these results provide a much richer understanding of MAEC and suggest bacterial processes that may underlie the clinical diversity associated with mastitis and their adaptation to this unique environment.

An in vitro evaluation of the effect of antimicrobial treatment on bovine mammary microbiota

Antimicrobial-resistant bacteria have been an increasing problem in human medicine and animal husbandry since the introduction of antimicrobials on the market in the 1940s. Over the last decades, efforts to reduce antimicrobial usage in animal husbandry have been shown to limit the development of resistant bacteria. Despite this, antimicrobial-resistant bacteria are still commonly detected and isolated worldwide. In this study, we investigated the presence of antimicrobial-resistant bacteria in bovine milk samples using a multiple approach based on culturing and amplicon sequencing. We first enriched milk samples obtained aseptically from bovine udders in the presence of two antimicrobials commonly used to treat mastitis and then described the resistant microbiota by amplicon sequencing and isolate characterization. Our results show that several commensal species and mastitis pathogens harbor antimicrobial resistance and dominate the enriched microbiota in milk in presence of antimicrobial agents. The use of the two different antimicrobials selected for different bacterial taxa and affected the overall microbial composition. These results provide new information on how different antimicrobials can shape the microbiota which is able to survive and reestablish in the udder and point to the fact that antimicrobial resistance is widely spread also in commensal species.

From Herd Health to Public Health: Digital Tools for Combating Antibiotic Resistance in Dairy Farms

The emergence of antimicrobial resistance (AMR) is a significant threat to global food security, human health, and the future of livestock production. Higher rates of antimicrobial use in dairy farming and the sheer lack of new antimicrobials available for use focused attention on the question of how the dairy production sector contributed to the development of AMR and paved the path toward taking action to curtail it on the targeted type of farms. This paper aims to provide an introduction to a phenomenon that has gained considerable attention in the recent past due to its ever-increasing impact, the use of antimicrobial drugs, the emergence of antimicrobial resistance (AMR) on dairy farms, and seeks to discuss the possibilities of approaches such as digital health monitoring and precision livestock farming. Using sensors, data, knowledge, automation, etc., digital health monitoring, as well as Precision Livestock Farming (PLF), is expected to enhance health control and minimize disease and antimicrobial usage. The work presents a literature review on the current status and trends of AMR in dairy farms, an understanding of the concept of digital health monitoring and PLF, and the presentation and usefulness of digital health monitoring and PLF in preventing AMR. The study also analyses the strengths and weaknesses of adopting and incorporating digital technologies and artificial intelligence for dairy farming and presents areas for further study and level of use.

Discriminating bovine mastitis pathogens by combining loop-mediated isothermal amplification and amplicon-binding split trehalase assay

Bovine mastitis is predominantly caused by intramammary infections with various Gram-positive and Gram-negative bacteria, requiring accurate pathogen identification for effective treatment and antimicrobial resistance prevention. Here, a novel diagnostic method was developed to detect mastitis pathogens in milk samples by combining loop-mediated isothermal amplification with a split enzyme biosensor whereby trehalase fragments were fused with a DNA-binding protein, SpoIIID. Three primer sets, LAMPstaph, LAMPstrep, and LAMPneg, harboring SpoIIID recognition sequences targeted Staphylococcus, Streptococcus, and Gram-negative pathogens, respectively. Limits of detection were determined for DNA extracted from bacterial culture and bacteria-spiked milk. The combined method detected as low as 2, 24, and 10 copies of genomic DNA of staphylococci, streptococci and Escherichia coli and 11 CFU/ml for milk spiked with Escherichia coli. Higher detection limits were observed for Gram-positive bacteria in spiked milk. When testing genomic DNA of 10 mastitis isolates at concentrations of 106 and 103 copies per reaction, no cross-reactivity was detected for LAMPstaph nor LAMPstrep, whereas the LAMPneg assay cross-reacted only with Corynebacterium sp. at the highest concentration. This combined method demonstrated the potential to distinguish mastitis pathogenic Gram types for a rapid decision of antimicrobial treatment without culturing.

Biomarker and proteome analysis of milk from dairy cows with clinical mastitis: Determining the effect of different bacterial pathogens on the response to infection

Antimicrobial usage (AMU) could be reduced by differentiating the causative bacteria in cases of clinical mastitis (CM) as either Gram-positive or Gram-negative bacteria or identifying whether the case is culture-negative (no growth, NG) mastitis. Immunoassays for biomarker analysis and a Tandem Mass Tag (TMT) proteomic investigation were employed to identify differences between samples of milk from cows with CM caused by different bacteria. A total of 94 milk samples were collected from cows diagnosed with CM across seven farms in Scotland, categorized by severity as mild (score 1), moderate (score 2), or severe (score 3). Bovine haptoglobin (Hp), milk amyloid A (MAA), C-reactive protein (CRP), lactoferrin (LF), α-lactalbumin (LA) and cathelicidin (CATHL) were significantly higher in milk from cows with CM, regardless of culture results, than in milk from healthy cows (all P-values <0.001). Milk cathelicidin (CATHL) was evaluated using a novel ELISA technique that utilises an antibody to a peptide sequence of SSEANLYRLLELD (aa49-61) common to CATHL 1-7 isoforms. A classification tree was fitted on the six biomarkers to predict Gram-positive bacteria within mastitis severity scores 1 or 2, revealing that compared to the rest of the samples, Gram-positive samples were associated with CRP < 9.5 μg/ml and LF ≥ 325 μg/ml and MAA < 16 μg/ml. Sensitivity of the tree model was 64%, the specificity was 91%, and the overall misclassification rate was 18%. The area under the ROC curve for this tree model was 0.836 (95% bootstrap confidence interval: 0.742; 0.917). TMT proteomic analysis revealed little difference between the groups in protein abundance when the three groups (Gram-positive, Gram-negative and no growth) were compared, however when each group was compared against the entirety of the remaining samples, 28 differentially abundant protein were identified including β-lactoglobulin and ribonuclease. Whilst further research is required to draw together and refine a suitable biomarker panel and diagnostic algorithm for differentiating Gram- positive/negative and NG CM, these results have highlighted a potential panel and diagnostic decision tree. Host-derived milk biomarkers offer significant potential to refine and reduce AMU and circumvent the many challenges associated with microbiological culture, both within the lab and on the farm, while providing the added benefit of reducing turnaround time from 14 to 16 h of microbiological culture to just 15 min with a lateral flow device (LFD).

Prevalence and antimicrobial resistance profiles of mastitis causing bacteria isolated from dairy goats in Mukurweini Sub-County, Nyeri County, Kenya

BACKGROUND

Ruminant mastitis continues to be a cause of economic losses in the dairy industry and remains a major public health hazard globally.

OBJECTIVES

This cross-sectional study was carried out in Mukurweini Sub-County of Nyeri County, Kenya, to investigate the prevalence of bacteria causing mastitis, risk factors associated with goat mastitis and the antibiotic resistance profiles of bacteria isolated from the goat milk.

METHODS

Farm level data on risk factors for mastitis was obtained from 56 farmers using a semi structured questionnaire. A total of 189 goat milk samples were collected. The goat's udder was observed for signs of clinical mastitis and the California Mastitis Test (CMT) used to test the milk for sub-clinical mastitis. All samples were then cultured for morphological identification of bacteria and strain typing by Matrix Assisted Laser Desorption/Ionization (MALDI)-Time of Flight (ToF) technique. Antimicrobial susceptibility of the isolated Staphylococcus aureus, coagulase-negative Staphylococcus (CoNS), Escherichia coli, Klebsiella oxytoca, Pseudomonas spp., Enterobacter spp., Proteus vulgaris and Escherichia vulneris to eight commonly used antibiotics was done by the disc diffusion method and validated by determining the presence of antibiotic resistance genes (mecA and blaTEM) using polymerase chain reaction method.

RESULTS

The prevalence of clinical mastitis was 1.1% (2/189) while that of sub-clinical mastitis was 84.7% (160/189). Higher (p < 0.05) prevalence of mastitis was observed in goats whose houses were cleaned fortnightly and in cases where farmers used same towel to dry different does' udders during the milking process. Thirteen different bacterial species were isolated from the milk samples and identified by MALDI-ToF, and these included S. aureus (22.0%), CoNS (20.3%), E. coli (18.1%), Pseudomonas spp. (14.3%), Enterobacter spp. (10.4%), K. oxytoca (6.0%), E. vulneris (1.7%), P. vulgaris (1.7%), Raoutella ornithinolytica (1.7%), Stenotrophomonas maltophilia (1.1%), Pantoea agglomerans (1.1%), Serratia marcescens (1.1%) and Cedeceas spp. (0.6%). One hundred pathogenic bacterial isolates were randomly selected and tested for antibiotic sensitivity to eight antibiotics out of which S. aureus were 97.5% resistant to Oxacillin and 100% sensitive to Ciprofloxacin. The CoNSs were 100% resistant to Oxacillin and 100% sensitive to Ciprofloxacin. E. coli were 93.9% resistant to Oxacillin, 69.7% sensitive to Ciprofloxacin and 87.9% sensitive to both Amoxicillin/Clavulanic acid and Meropenem. The antimicrobial resistant genes detected in S. aureus and E. coli were mecA [66.7%, 0%], and blaTEM [20% and 78.3%], respectively.

CONCLUSION

In conclusion, the study showed that most of the does were affected by subclinical mastitis with the main causative bacteria being Staphylococci spp. and coliforms. Farmers need to be trained on improved control of mastitis by adoption of good milking practices and use of CMT kit for early detection of mastitis. Occurrence of multidrug resistance by key mastitis causing pathogens was shown to be prevalent and therefore there is need for development of intervention strategies.

Extended-Spectrum Beta-Lactamase-Producing Escherichia coli and Other Antimicrobial-Resistant Gram-Negative Pathogens Isolated from Bovine Mastitis: A One Health Perspective

Antimicrobial resistance (AMR) poses an imminent threat to global public health, driven in part by the widespread use of antimicrobials in both humans and animals. Within the dairy cattle industry, Gram-negative coliforms such as Escherichia coli and Klebsiella pneumoniae stand out as major causative agents of clinical mastitis. These same bacterial species are frequently associated with severe infections in humans, including bloodstream and urinary tract infections, and contribute significantly to the alarming surge in antimicrobial-resistant bacterial infections worldwide. Additionally, mastitis-causing coliforms often carry AMR genes akin to those found in hospital-acquired strains, notably the extended-spectrum beta-lactamase genes. This raises concerns regarding the potential transmission of resistant bacteria and AMR from mastitis cases in dairy cattle to humans. In this narrative review, we explore the distinctive characteristics of antimicrobial-resistant E. coli and Klebsiella spp. strains implicated in clinical mastitis and human infections. We focus on the molecular mechanisms underlying AMR in these bacterial populations and critically evaluate the potential for interspecies transmission. Despite some degree of similarity observed in sequence types and mobile genetic elements between strains found in humans and cows, the existing literature does not provide conclusive evidence to assert that coliforms responsible for mastitis in cows pose a direct threat to human health. Finally, we also scrutinize the existing literature, identifying gaps and limitations, and propose avenues for future research to address these pressing challenges comprehensively.

The effect of heat stress on performance, fertility, and adipokines involved in regulating systemic immune response during lipolysis of early lactating dairy cows

The aim of this study was to assess the potential effect of heat stress on dairy cow productivity, fertility, and biochemical blood indices during the early lactation stage in a temperate climate. Additionally, the study aimed to determine the role of leptin and adiponectin in regulating the immune response accompanying lipolysis after calving in dairy cows. The study included 100 clinically healthy Polish Holstein-Friesian dairy cows selected based on parity and 305 d of milk yield from 5 commercial farms with similar herd management and housing systems. Prospective cohort data were recorded from calving day until 150 d in milk, and microclimate loggers installed inside the barns were used to record temperature and relative humidity data to calculate daily temperature-humidity index (THI) on the calving day, through +7, +14, and +21 d during early lactation. Additionally, monthly productive performance parameters such as milk yield, chemical composition, fatty acids composition, and fertility indices were analyzed. Results showed that the THI from calving day through +7, +14, and +21 d during early lactation was negatively associated with fertility parameters such as delayed first estrus postpartum and an elongated calving interval, respectively, by 29, 27, 25, and 16 d. Furthermore, an increase in THI value during early lactation was associated with an elongated artificially inseminated service period, days open, and intercalving period. Increasing THI from calving day (0 d) through +7, +14, and up to +21 d during early lactation was also linked to decreased milk yield by 3.20, 4.10, 5.60, and 5.60 kg, respectively. The study also found that heat stress during early lactation was associated with a lower body condition score in dairy cows and higher concentrations of leptin, nonesterified fatty acids, and β-hydroxybutyrate, accompanied by a drastic reduction in adipose tissue-secreted adiponectin levels after calving. Additionally, heat stress-induced lipolysis in adipose tissue caused an inflammatory response that increased biochemical blood indices associated with immune responses such as cytokines, acute phase proteins, and heat shock protein. These findings suggest that exposing dairy cows to heat stress during early lactation can negatively affect their productive performance, fertility, and biochemical blood indices in subsequent lactations. Thus, farm management changes should be implemented during early lactation to mitigate the negative consequences of heat stress occurrence.

Occurence of antimicrobial residues in milk and labneh consumed in Lebanon

Antimicrobials are administered in livestock for different uses leading to milk contamination and several undesirable effects. Because there is a lack of surveillance of antimicrobial residues (AMRs) in milk and dairy products in Lebanon, this study aims to determine the occurrence of AMRs in 90 Lebanese samples of milk and labneh (concentrated yoghurt). Multi-residue screening methods with suitable sample preparations were applied to detect 71 AMRs in milk and labneh, respectively, using LC-MS/MS. Of the total number of samples, 71% was contaminated with AMRs and (fluoro)quinolones and macrolides were the most detected families. Additional confirmation tests proved that 6.7% of the milk samples were non-compliant for the macrolides tilmicosin, tulathromycin and spiramycin. Moreover, some labneh prepared from contaminated milk samples was analysed to determine the fate of AMRs during the manufacturing process. The results showed that some AMRs could be concentrated, eliminated or degraded, based on their physicochemical characteristics.

Determining the prevalence and genetic diversity of plasmid-mediated sulfonamide resistance in Escherichia coli from commercial broiler samples

Sulfonamides are commonly used antibacterials in commercial poultry, contributing toward the development of multidrug-resistant (MDR) phenotypes among Escherichia coli and that has emerged as global concern. The current study aimed to assess the sulfonamide resistance among isolated E. coli strains among commercial broilers. The bacterial strains were identified from fecal samples (n = 100) using selective media, followed by initial identification based on biochemical profiles. The susceptibility was determined by measuring the minimum inhibitory concentration (MIC) against sulfamethoxazole. The study also evaluated mobile genetic elements (MGEs), the mediators of antibiotic resistance, by amplification of plasmid DNA using specific primer PCR. Additionally, the isolates were subjected to multilocus sequence typing (MLST) analysis to investigate the genetic diversity among E. coli carrying sulfonamide resistance genes. The results revealed that 58% (58/100) E. coli strains were resistant to sulfonamides, with 36.20% (21/58) of the strains exhibiting an MIC breakpoint ≥512 µg/mL. PCR analysis showed that 42.85% (9/21) of the strains harbored the sul-1 gene, while 38.09% (8/21) carried the sul-2 gene, and 19.04% (4/21) had both genes. No isolate showed the presence of the sul-3 gene. Furthermore, class 1 and class 2 integrons were identified among 80.95% (17/21) and 19.04% (4/21) of the strains, respectively. MLST analysis confirmed that the strains belonged to sequence types (STs) including ST1638, ST155, ST48, ST350, ST23, ST156, and ST746. These findings underscore the diversity among E. coli strains in commercial poultry, which poses a significant risk.

Genes and pathways revealed by whole transcriptome analysis of milk derived bovine mammary epithelial cells after Escherichia coli challenge

Mastitis, inflammation of the mammary gland, is the costliest disease in dairy cattle and a major animal welfare concern. Mastitis is usually caused by bacteria, of which staphylococci, streptococci and Escherichia coli are most frequently isolated from bovine mastitis. Bacteria activate the mammary immune system in variable ways, thereby influencing the severity of the disease. Escherichia coli is a common cause of mastitis in cattle causing both subclinical and clinical mastitis. Understanding of the molecular mechanisms that activate and regulate the host response would be central to effective prevention of mastitis and breeding of cows more resistant to mastitis. We used primary bovine mammary epithelial cell cultures extracted noninvasively from bovine milk samples to monitor the cellular responses to Escherichia coli challenge. Differences in gene expression between control and challenged cells were studied by total RNA-sequencing at two time points post-challenge. In total, 150 and 440 (Padj < 0.05) differentially expressed genes were identified at 3 h and 24 h post-challenge, respectively. The differentially expressed genes were mostly upregulated at 3 h (141/150) and 24 h (424/440) post-challenge. Our results are in line with known effects of E. coli infection, with a strong early inflammatory response mediated by pathogen receptor families. Among the most significantly enriched early KEGG pathways were the TNF signalling pathway, the cytokine-cytokine receptor interaction, and the NF-kappa B signalling pathway. At 24 h post-challenge, most significantly enriched were the Influenza A, the NOD-like receptor signalling, and the IL-17 signaling pathway.

Treatment of clinically severe bovine mastitis - a scoping review

Mastitis is a major health problem for bovines and can be categorized as non-severe or severe, based on clinical symptoms. A severe case of clinical mastitis is usually defined by the cow being affected systemically. It is important to consider how to handle severe cases because these cases can be fatal and cause high production losses. However, there are generally few detailed treatment guidelines. By conducting a scoping review on the topic, we aimed to synthesize the information that is available on treatment and outcomes, as reported from clinical trials and observational studies. This was facilitated by following the PRISMA-guidelines with a stepwise systematic screening of scientific literature on the subject, retrieved via Pubmed and Web of Science, using pre-defined selection criteria. The results yielded a total of 14 reports of treatment and outcomes in cases of naturally occurring severe clinical mastitis. Cross-trial comparison was difficult due to the different exclusion criteria and outcome definitions. Many studies focused on cases caused by gram-negative bacteria treated with intensive antibiotic protocols, often containing antibiotics that are categorized as critical for human health. Few focused on severe cases caused by gram-positive bacteria or on the relative use of non-antibiotic treatment. In general, only a small number of statistically significant differences were found in trials comparing different treatment protocols, with no obvious trends across trials. Our findings emphasize the need for more research into the treatment efficacy of antibiotic and non-antibiotic options for clinically severe mastitis. Furthermore, consideration of how trial conditions relate to the practical circumstances in a field setting could improve the applicability of reported results. This could help to provide practitioners with the information needed to make evidence-based treatment decisions in cases of clinically severe mastitis.

Accuracy of an AI-based automated plate reading mobile application for the identification of clinical mastitis-causing pathogens in chromogenic culture media

Using on-farm microbiological culture (OFC), based on chromogenic culture media, enables the identification of mastitis causing pathogens in about 24 h, allows rapid decision making on selective treatment and control management measures of cows with clinical mastitis (CM). However, accurate interpretation of OFC results requires trained and experienced operators, which could be a limitation for the use of OFC in dairy farms. Our hypothesis was that AI-based automated plate reading mobile application can analyze images of microorganisms' colonies in chromogenic culture media with similar diagnostic performance as a trained specialist evaluator. Therefore, the aim of the present study was to evaluate the diagnostic accuracy of an AI-based application (Rumi; OnFarm, Piracicaba, São Paulo, Brazil) for interpreting images of mastitis causing microorganism colonies grown in chromogenic culture media. For this study two trials were organized to compare the results obtained using an AI-based application Rumi with the interpretation of: (1) a trained specialist, using MALDI-TOF MS as the gold standard; (2) farm personnel users (FPU). In trial 1, a total of 476 CM milk samples, from 11 farms located in São Paulo (n = 7) and Minas Gerais (n = 4), southeast Brazil, were inoculated in chromogenic culture media plates (Smartcolor 2, OnFarm, Piracicaba, São Paulo, Brazil) by specialists under lab conditions, and digital images were recorded 24 h after incubation at 37 °C. After that, all the 476 digital images were analyzed by the Rumi and by another specialist (who only had access to the digital images) and the diagnostic accuracy indicators sensitivity (Se) and specificity (Sp) were calculated using MALDI-TOF MS microbiological identification of the isolates as the reference. In Trial 2, a total of 208 CM milk samples, from 150 farms from Brazil, were inoculated in chromogenic culture media plates by FPU, and the results of microbiological growth were visually interpreted by FPU under on-farm conditions. After visual interpretation, results were recorded using an OnFarmApp application (herd manage application for mastitis by OnFarm, Piracicaba, São Paulo, Brazil), and the images of the chromogenic culture plates were captured by the OnFarmApp to be evaluated by Rumi and Bayesian Latent Class Models were performed to compare Rumi and the FPU. In Trial 1, Rumi presented high and intermediate accuracy results, with the only exception of the low Enterococcus spp.'s Se. In comparison with the specialist, Rumi performed similarly in Se and Sp for most groups of pathogens, with the only exception of non-aureus staphylococci where Se results were lower. Both Rumi and the specialist achieved Sp results > 0.96. In Trial 2, Rumi had similar results as the FPU in the Bayesian Latent Class Model analysis. In conclusion, the use of the AI-based automated plate reading mobile application can be an alternative for visual interpretation of OFC results, simplifying the procedures for selective treatment decisions for CM based on OFC.

Assessment of antibiotic use patterns in bovine mastitis treatment in the dairy sector in Serbia

The dairy sector is essential for the world's food systems, playing a vital role in agricultural production. Yet, mastitis, an inflammation of the mammary gland, affects a considerable portion of the dairy cow population annually, leading to reduced productivity and sustainability. Insight into therapeutic protocols is essential for a better understanding of the situation on farms with the aim of developing new or harmonizing existing protocols in the mastitis treatment. This study conducted on dairy farm in Serbia aimed to explore the most commonly used antibiotics during bovine mastitis treatment and their association with daily milk yield. Data from 100 lactating cows, including therapeutic protocols, lactation numbers, mastitis episodes, milk yield, and antibiotic usage, were obtained from a computerized database and statistically analysed. The results demonstrated a high prevalence of narrow-spectrum antibiotics usage, with the majority of cows treated with combination therapy. The route of antibiotic application did not significantly impact daily milk yield, while treatment duration had no discernible effect. Nonetheless, specific antibiotics were associated with milk yield variations, suggesting the need for careful antibiotic selection and management in mastitis therapy. These findings emphasize the importance of prudent antibiotic use to safeguard animal health and long-term milk production sustainability.

Bacteremia in Severe Mastitis of Dairy Cows

The aim of this cross-sectional study was to investigate the occurrence of bacteremia in severe mastitis cases of dairy cows. Milk and corresponding blood samples of 77 cases of severe mastitis were bacteriologically examined. All samples (milk and blood) were incubated aerobically and anaerobically to also investigate the role of obligate anaerobic microorganisms in addition to aerobic microorganisms in severe mastitis. Bacteremia occurred if identical bacterial strains were isolated from milk and blood samples of the same case. In addition, pathogen shedding was examined, and the data of animals and weather were collected to determine associated factors for the occurrence of bacteremia in severe mastitis. If Gram-negative bacteria were detected in milk samples, a Limulus test (detection of endotoxins) was also performed for corresponding blood samples without the growth of Gram-negative bacteria. In 74 cases (96.1%), microbial growth was detected in aerobically incubated milk samples. The most-frequently isolated bacteria in milk samples were Escherichia (E.) coli (48.9%), Streptococcus (S.) spp. (18.1%), and Klebsiella (K.) spp. (16%). Obligatory anaerobic microorganisms were not isolated. In 72 cases (93.5%) of the aerobically examined blood samples, microbial growth was detected. The most-frequently isolated pathogens in blood samples were non-aureus Staphylococci (NaS) (40.6%) and Bacillus spp. (12.3%). The Limulus test was positive for 60.5% of cases, which means a detection of endotoxins in most blood samples without the growth of Gram-negative bacteria. Bacteremia was confirmed in 12 cases (15.5%) for K. pneumoniae (5/12), E. coli (4/12), S. dysgalactiae (2/12), and S. uberis (1/12). The mortality rate (deceased or culled) was 66.6% for cases with bacteremia and 34.1% for cases without bacteremia. High pathogen shedding and high humidity were associated with the occurrence of bacteremia in severe mastitis.

Alternatives to antibiotics for treatment of mastitis in dairy cows

Mastitis is considered the costliest disease on dairy farms and also adversely affects animal welfare. As treatment (and to a lesser extent prevention) of mastitis rely heavily on antibiotics, there are increasing concerns in veterinary and human medicine regarding development of antimicrobial resistance. Furthermore, with genes conferring resistance being capable of transfer to heterologous strains, reducing resistance in strains of animal origin should have positive impacts on humans. This article briefly reviews potential roles of non-steroidal anti-inflammatory drugs (NSAIDs), herbal medicines, antimicrobial peptides (AMPs), bacteriophages and their lytic enzymes, vaccination and other emerging therapies for prevention and treatment of mastitis in dairy cows. Although many of these approaches currently lack proven therapeutic efficacy, at least some may gradually replace antibiotics, especially as drug-resistant bacteria are proliferating globally.

Invited review: Selective treatment of clinical mastitis in dairy cattle

Treatment of clinical mastitis (CM) and use of antimicrobials for dry cow therapy are responsible for the majority of animal-defined daily doses of antimicrobial use (AMU) on dairy farms. However, advancements made in the last decade have enabled excluding nonsevere CM cases from antimicrobial treatment that have a high probability of cure without antimicrobials (no bacterial causes or gram-negative, excluding Klebsiella spp.) and cases with a low bacteriological cure rate (chronic cases). These advancements include availability of rapid diagnostic tests and improved udder health management practices, which reduced the incidence and infection pressure of contagious CM pathogens. This review informed an evidence-based protocol for selective CM treatment decisions based on a combination of rapid diagnostic test results, review of somatic cell count and CM records, and elucidated consequences in terms of udder health, AMU, and farm economics. Relatively fast identification of the causative agent is the most important factor in selective CM treatment protocols. Many reported studies did not indicate detrimental udder health consequences (e.g., reduced clinical or bacteriological cures, increased somatic cell count, increased culling rate, or increased recurrence of CM later in lactation) after initiating selective CM treatment protocols using on-farm testing. The magnitude of AMU reduction following a selective CM treatment protocol implementation depended on the causal pathogen distribution and protocol characteristics. Uptake of selective treatment of nonsevere CM cases differs across regions and is dependent on management systems and adoption of udder health programs. No economic losses or animal welfare issues are expected when adopting a selective versus blanket CM treatment protocol. Therefore, selective CM treatment of nonsevere cases can be a practical tool to aid AMU reduction on dairy farms.

Association between Mastitis Occurrence in Dairy Cows and Bedding Characteristics of Compost-Bedded Pack Barns

Compost-bedded pack barns (CB) are receiving increasing attention as a housing system that can potentially improve the welfare of dairy cows. This study characterized the frequency and profile of pathogens isolated from clinical (CM) and subclinical (SCM) mastitis in dairy cows housed in CB. It evaluated the association between mastitis occurrence and bedding characteristics in CB systems. Over six months, seven dairy herds were visited monthly for milk and bedding sample collections. Milk samples from mastitis cases were submitted to microbiological identification by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF MS). Bedding samples were submitted to physical-chemical (pH, organic matter, moisture, and carbon to nitrogen ratio) and microbiological counting (total bacterial counts, coliforms, streptococci, and staphylococci) analyses. Regression analysis was used to determine the association between mastitis occurrence and CB characteristics. Our results showed that Escherichia coli and environmental streptococci were the most frequently isolated pathogens from CM cases, while Staphylococcus chromogenes and contagious pathogens (Staphylococcus aureus and Streptococcus agalactiae) were the most commonly isolated from SCM cases. Bedding moisture content was positively associated with the incidence of CM. The bedding carbon to nitrogen ratio was negatively associated with the incidence of SCM, and the bedding total bacteria counts tended to be associated with the incidence of SCM. Bedding counts of coliforms positively associated with the prevalence of SCM. Our results can support decision-makers in the dairy industry seeking strategies for bedding management and mastitis control.

Efficiency of conventional and nanoparticle oxytetracycline in treatment of clinical endometritis in postpartum dairy cows

The incidence of clinical endometritis in dairy cows postpartum is one of the important reasons for financial losses in the dairy industry. The costs of treatment, milk losses, infertility, repeated breeding, and high annual culling rate of dairy cows present immediate losses in case of treatment failure. The commonly used therapeutic methods for clinical endometritis have not been successful nor have given definitive solutions to overcome the complications of the disease in dairy cows. Therefore, it was necessary to propose an innovative treatment program to overcome the reasons for the failure and lack of effectiveness of the treatment of clinical endometritis. This was tackled in the current study; oxytetracycline with different concentrations, oxytetracycline 5% (OTCC5%), oxytetracycline 20% (OTCC20%), and oxytetracycline 20% nanoparticles (OTC-NPs) were used for the treatment of clinical endometritis. Diagnosis of clinical endometritis was based on the assessment of high serum concentration of pro-inflammatory cytokines, acute phase protein, increased endometrium thickness, and intrauterine discharges with different degrees of echogenicity monitored by ultrasonography. Application of OTC-NPs revealed a decrease in serum concentration of pro-inflammatory cytokines (IL-1, IL-6, and TNF-α) and acute phase proteins compared to OTCC20% and OTCC5% groups. The improvement achieved by OTC-NPs may be attributed to the reduction of OTC particles into nano size which facilitates its tissue bioavailability, dispersion, penetration power to deeper tissues, and its more broad-spectrum activities. These activities were clearly apparent after the evacuation of uterine contents using a single dose of PGF2α. The OTC-NPs revealed a reduction in serum concentration of cytokines compared to OTCC20% and OTCC5% groups arranged as follows: 10.11, 25.45, 35.56 for IL-1; 99, 300, 319 for IL-6; 1.01, 4.40, 8.06 for CRP; and 46, 183, 266 for TNF-α. Furthermore, an increase in serum concentration of albumin (3.34) was obtained by OTC-NPs compared to OTCC5% (1.70). This improvement can be taken as evidence of liver resumption functions and inflammatory reactions. On the other side, globulin concentration recorded an increase like albumin and total proteins in OTC-NPs compared to others. A reduction in the endometrium thickness in OTC-NPs with the disappearance of intrauterine discharges was monitored by ultrasonography. This confirmed the subsiding of clinical endometritis in OTC-NPs group. Moreover, a significant improvement in conception and pregnancy rate in OTC-NPs compared to other groups were observed.

Cell membrane-coated nanoparticles: An emerging antibacterial platform for pathogens of food animals

Bacterial pathogens of animals impact food production and human health globally. Food animals act as the major host reservoirs for pathogenic bacteria and thus are highly prone to suffer from several endemic infections such as pneumonia, sepsis, mastitis, and diarrhea, imposing a major health and economical loss. Moreover, the consumption of food products of infected animals is the main route by which human beings are exposed to zoonotic bacteria. Thus, there is excessive and undue administration of antibiotics to fight these virulent causative agents of food-borne illness, leading to emergence of resistant strains. Thus, highprevalence antibiotic-resistant resistant food-borne bacterial infections motivated the researchers to discover new alternative therapeutic strategies to eradicate resistant bacterial strains. One of the successful therapeutic approach for the treatment of animal infections, is the application of cell membrane-coated nanoparticles. Cell membranes of several different types of cells including platelets, red blood cells, neutrophils, cancer cells, and bacteria are being wrapped over the nanoparticles to prepare biocompatible nanoformulations. This diversity of cell membrane selection and together with the possibility of combining with an extensive range of nanoparticles, has opened a new opportunistic window for the development of more potentially effective, safe, and immune evading nanoformulations, as compared to conventionally used bare nanoparticle. This article will elaborately discuss the discovery and development of novel bioinspired cell membrane-coated nanoformulations against several pathogenic bacteria of food animals such as Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Salmonella enteritidis, Campylobacter jejuni, Helicobacter pylori, and Group A Streptococcus and Group B Streptococcus.

Animal board invited review: The contribution of adipose stores to milk fat: implications on optimal nutritional strategies to increase milk fat synthesis in dairy cows

A wide range of nutritional and non-nutritional factors influence milk fat synthesis and explain the large variation observed in dairy herds. The capacity of the animal to synthesize milk fat will largely depend on the availability of substrates for lipid synthesis, some of which originate directly from the diet, ruminal fermentation or from adipose tissue stores. The mobilization of non-esterified fatty acids from adipose tissues is important to support the energy demands of milk synthesis and will therefore have an impact on the composition of milk lipids, especially during the early lactation period. Such mobilization is tightly controlled by insulin and catecholamines, and in turn, can be affected indirectly by factors that influence these signals, namely diet composition, lactation stage, genetics, endotoxemia, and inflammation. Environmental factors, such as heat stress, also impact adipose tissue mobilization and milk fat synthesis, mainly through endotoxemia and an immune response-related increase in concentrations of plasma insulin. Indeed, as proposed in the present review, the central role of insulin in the control of lipolysis is key to improving our understanding of how nutritional and non-nutritional factors impact milk fat synthesis. This is particularly the case during early lactation, as well as in situations where mammary lipid synthesis is more dependent on adipose-derived fatty acids.

Antimicrobial use and its association with the presence of methicillin-resistant staphylococci (MRS) and extended-spectrum beta-lactamases (ESBL)-producing coliforms in mastitic milk on dairy farms in the Chiba Prefecture, Japan

Food-producing animals, including dairy cattle, are potential reservoirs of antimicrobial resistance. However, there is limited data on antimicrobial use and the selection of resistant bacteria. Therefore, we investigated the association between antimicrobial use and resistance to mastitis pathogens using 2016 data from milk samples collected from cows with mastitis in 134 dairy farms in Chiba Prefecture, one of the principal dairy production prefectures in Japan. We recorded the antimicrobial use and isolation of methicillin-resistant staphylococci (MRS) and extended-spectrum beta-lactamase (ESBL)-producing coliforms (E. coli and Klebsiella spp.), and used the antimicrobial treatment incidence (ATI; the theoretical number of animals per 1000 animal-days subjected to antimicrobial treatment) to indicate antimicrobial use on each farm. The farms in which MRS or ESBL-producing coliforms were isolated from at least one mastitic milk sample were classified as antimicrobial resistance (AMR)-positive, and those in which neither MRS nor ESBL-producing coliforms were isolated were classified as AMR-negative. The AMR-positive farms showed a significantly higher ATI (median 45.17) than AMR-negative farms (median 38.40). The results indicate that high antimicrobial usage is associated with AMR in staphylococci and coliforms isolated from mastitic milk on dairy farms in Chiba Prefecture.

Mastitis: What It Is, Current Diagnostics, and the Potential of Metabolomics to Identify New Predictive Biomarkers

Periparturient diseases continue to be the greatest challenge to both farmers and dairy cows. They are associated with a decrease in productivity, lower profitability, and a negative impact on cows’ health as well as public health. This review article discusses the pathophysiology and diagnostic opportunities of mastitis, the most common disease of dairy cows. To better understand the disease, we dive deep into the causative agents, traditional paradigms, and the use of new technologies for diagnosis, treatment, and prevention of mastitis. This paper takes a systems biology approach by highlighting the relationship of mastitis with other diseases and introduces the use of omics sciences, specifically metabolomics and its analytical techniques. Concluding, this review is backed up by multiple studies that show how earlier identification of mastitis through predictive biomarkers can benefit the dairy industry and improve the overall animal health.

Comparison of the Efficacy of Intramammary or Injectable Antibiotic Administration against Staphylococcal Mastitis in Ewes

The objectives of the work were (a) to compare the efficacy of two routes for antibiotic administration in the treatment of mastitis in ewes and (b) to assess the potential importance of the timing of the initiation of the therapeutic regime on the outcome of the treatment. The ewes were allocated at random into three equal groups; intramammary inoculation with a Staphylococcus simulans isolate was performed, and clinical mastitis developed. The ewes in groups T1 (n = 6) and T2 (n = 6) were treated by the intramammary administration of ampicillin and dicloxacillin (two administrations with a 12-h interval). The ewes in group T3 (n = 6) were treated by the intramuscular injection of ampicillin and dicloxacillin (0.75 mL per 10 kg bodyweight, three injections with a 24-h interval). In the ewes in groups T1 and T3, treatment started immediately when the clinical signs of mastitis were first detected during the periodic examination of the ewes; in the ewes in group T2, treatment started 24 h after the clinical signs of mastitis were first detected. The animals were monitored clinically; mammary secretion samples were collected for bacteriological and cytological examinations. The median duration of the clinical signs was 4.75, 7.13, and 4.75 d for T1, T2, and T3; significant differences in clinical severity between the groups were seen until the 7th day post-treatment. The median duration of bacterial recovery was 3.25, 8.00, and 8.00 d for T1, T2, and T3; significant differences in the frequency of bacterial recovery between the groups were seen until (64.1%, 94.9%, and 96.2% of the samples) and after (2.9%, 16.7%, and 11.8%) the 7th day post-treatment. The median period required for the complete cure (clinical, bacteriological, and cytological) was shorter in the T1 than in the T2 and T3 ewe groups: 20.0, 32.0, and 24.5 d, respectively. The findings cover a gap in the available literature regarding the treatment of clinical mastitis in ewes. Early treatment resulted in the improved cure of the infection. The comparison of the intramammary and injectable routes for antibiotic administration indicated some benefit for the former, primarily in the post-treatment somatic cell counts.

Association of pre-treatment somatic cell counts with bacteriological cure following diagnosis of intramammary infection

Antibiotic administration is crucial to ensure the health and productivity of dairy cattle. Mastitis is a disease that is typically a result of an intramammary infection (IMI), and antibiotic regimens are implemented to aid in curing IMI. Diagnosis is usually by detection of elevated milk somatic cell counts (SCC) and/or presence of culturable pathogens in the milk. Antibiotic treatment success is associated with the SCC at the time of treatment, though this correlation is still poorly understood. The objective of this project was to evaluate pre-treatment SCC and its association with IMI cure incidence following a standard antibiotic treatment. We hypothesized that pre-treatment SCC would be significantly lower in cases where the IMI ultimately cured compared to cases where the IMI failed to cure. Milk samples were collected aseptically from lactating cow quarters experiencing clinical or subclinical mastitis (n = 52). Clinical mastitis was diagnosed by a trained milking technician and subclinical mastitis was diagnosed at the quarter level as a SCC > 200,000 cells/mL and presence of bacterical growth in milk at time of treatment. After collection of the day 0 (D0) milk samples, the SCC was enumerated, and the milk sample cultured. Intramammary antibiotic therapy Cetftiofur hydrochloride (Spectramast® LC) was administered once/day for 5 days. Post-treatment samples were collected 14 d (D14) and 28 d (D28) later. A bacteriological cure was confirmed when both the D14 and D28 samples were free of culturable pathogens. The overall cure rate was 46.2%. Interestingly, the cure rates of antibiotic therapy decreased as pre-treatment SCC increased. Quarters that experienced bacteriological cure demonstrated a lower pre-treatment SCC (507,041 cells/mL ± 127.86 SEM, P = 0.01) compared to cows that did not cure, which had high pre-treatment SCC (1,640,392 cells/mL ± 333.28 SEM). Quarters that failed to cure had higher SCC values 28 days post-treatment in comparison to quarters that cured (P < 0.001). Future studies should investigate whether we can develop unique SCC-dependent mastitis treatment protocols which increase mastitis cure rates and enhance overall mammary health.

Antimicrobial use and resistance in food-producing animals-How can we protect the efficacy of antibiotics for reproductive diseases?

The ongoing emergence of antibiotic resistance jeopardizes efficacy of antibiotics in curing animals from bacterial infections that threaten their health, welfare and productivity. This review gives an overview of antimicrobial use data in food-producing animals, a discussion on how antimicrobials are used for some infections in the reproductive system in cattle, the horse and pig in Europe where there are differences in treatment practices including options to refine the use of antibiotics, and finally, a presentation of the antibiotic resistance for some bacteria collected from the reproductive system. It is shown that there are differences in applied treatment regimens for, as well as prevention of, several reproductive diseases in Europe. Some of the treatments are not evidence-based, which should be considered by clinicians and other stakeholders. It is concluded that a more refined and restrictive use of antibiotics could be achieved by adhering to evidence-based guidelines by national and international expertise including the scientific literature when available. This may call for a re-think among the animal health stakeholders regarding the use of antibiotics and may demand new skill-sets in the animal health sphere.

Escherichia coli Mastitis in Dairy Cattle: Etiology, Diagnosis, and Treatment Challenges

Bovine mastitis is an inflammation of the udder tissue parenchyma that causes pathological changes in the glandular tissue and abnormalities in milk leading to significant economic losses to the dairy industry across the world. Mammary pathogenic Escherichia (E.) coli (MPEC) is one of the main etiologic agents of acute clinical mastitis in dairy cattle. MPEC strains have virulence attributes to resist the host innate defenses and thrive in the mammary gland environment. The association between specific virulence factors of MPEC with the severity of mastitis in cattle is not fully understood. Furthermore, the indiscriminate use of antibiotics to treat mastitis has resulted in antimicrobial resistance to all major antibiotic classes in MPEC. A thorough understanding of MPEC’s pathogenesis and antimicrobial susceptibility pattern is required to develop better interventions to reduce mastitis incidence and prevalence in cattle and the environment. This review compiles important information on mastitis caused by MPEC (e.g., types of mastitis, host immune response, diagnosis, treatment, and control of the disease) as well as the current knowledge on MPEC virulence factors, antimicrobial resistance, and the dilemma of MPEC as a new pathotype. The information provided in this review is critical to identifying gaps in knowledge that will guide future studies to better design diagnostic, prevent, and develop therapeutic interventions for this significant dairy disease.

Phenotyping and genotyping studies on extended-spectrum β-lactamase-producing Escherichia coli isolates from mastitic cows on dairy farms in Egypt

Background and Aim: Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae have become a serious public health hazard worldwide. This importance is derived from the increase of new variants, particularly blaTEM, blaSHV, and blaCTX-M genes. This study aimed to examine ESBL-producing Escherichia coli isolated from different governorates in Egypt from dairy cows infected with subclinical and clinical mastitis. Materials and Methods: This study examined 207 milk samples for the resistance of isolates against 14 different antibiotics and ran serological identification of ESBL-producing E. coli isolates with complete antibiotic resistance. Genotypic and sequencing analyses of several resistance genes were conducted using a polymerase chain reaction. Results: E. coli was identified in cases with subclinical mastitis (80.5%) and clinical mastitis (85.7%). ESBL-producing E. coli was isolated from 38.2% of subclinical mastitic milk compared to 39.3% in clinical cases, where O26:k60, O125:k70, and O25:k11 were the serotypes with complete resistance to antibiotics. ESBL-producing E. coli isolates were resistant to cefotaxime, amoxicillin, cloxacillin, oxacillin, rifampicin, and penicillin in 100% but susceptible to amoxicillin and clavulanic acid in 82.5% of the cases. Results also revealed that 51.25%, 52.5%, 66.25%, 77.5% and 60% of ESBL-producing E. coli isolates were responsive to ciprofloxacin, ofloxacin, norfloxacin, levofloxacin, and gentamycin, respectively. The detected genes were registered in GenBank as MW345819.1 and MW345820.1 for the E. coli blaTEM gene and MW295407 for the E. coli blaSHV gene. Conclusion: This study found ESBL-producing E. coli in mastitic milk samples from Egyptian dairy farms and confirmed the occurrence and circulation of the main antibiotic genes (blaTEM and blaSHV) in the samples. Regular and thorough surveillance of ESBL-producing E. coli and subsequent preventive actions are essential for preventing the spread of these resistance genes in the future, which could pose serious and catastrophic health risks. Authorities should cling to the concept of One Health to minimize the risk of new varieties.

Nanocurcumin alleviates inflammation and oxidative stress in LPS-induced mastitis via activation of Nrf2 and suppressing TLR4-mediated NF-κB and HMGB1 signaling pathways in rats

Coliform mastitis is a worldwide serious disease of the mammary gland. Curcumin is a pleiotropic polyphenol obtained from turmeric, but it is hydrophobic and rapidly eliminated from the body. However, nanoformulation of curcumin significantly improves its pharmacological activity by enhancing its hydrophobicity and oral bioavailability. Our study aimed to investigate the possible antioxidant and anti-inflammatory effects of nanocurcumin as a prophylactic against LPS-induced coliform mastitis in rat model, where LPS was extracted from a field strain of Escherichia coli (bovine mastitis isolate). The study was conducted on twenty lactating Wistar female rats divided into four equal groups, and the mastitis model was initiated by injection of LPS through the duct of the mammary gland. The results showed that nanocurcumin significantly attenuated the lipid peroxidation (MDA), oxidized glutathione, the release of pro-inflammatory cytokines (TNF-α and IL-1β), and the gene expression of TLR4, NF-κB p65, and HMGB1. Meanwhile, it improved the reduced glutathione level and Nrf2 activity and preserved the normal alveolar architecture. These findings suggested that nanocurcumin supplementation can be a promising potential protective approach for coliform mastitis.

Efficacy of antimicrobial therapy for bovine acute <i>Klebsiella pneumoniae </i>mastitis

The purpose of this retrospective study was to assess the efficacy of antimicrobial therapy for bovine acute Klebsiella pneumoniae mastitis. We evaluated data from cattle in Ehime, Japan, with naturally occurring acute mastitis due to K. pneumoniae (n=208) or Escherichia coli (n=201). Survival was significantly shorter in cattle with acute K. pneumoniae mastitis (median, 76 days) compared with the disease caused by E. coli (median 464 days). In 2004–2008, because both species were highly susceptible to cefazolin, cases of K. pneumoniae and E. coli mastitis were treated solely with cefazolin, yielding clinical cure rates of 52.8% for K. pneumoniae and 86.0% for E. coli. However, since 2009, the efficacy of treatment of K. pneumoniae mastitis with cefazolin alone has decreased. When cefazolin administered on the first disease day led to clinical improvement, treatment with cefazolin was continued. However, when cefazolin administered on the first disease day failed to yield clinical improvement, the antibiotic was switched to a fluoroquinolone on the second day, resulting in cure rates of 76.7% for K. pneumoniae and 80.0% for E. coli. These findings suggest that, when the first-line drug (e.g., cefazolin) is ineffective, promptly changing to a second-line drug (e.g., a fluoroquinolone) increases the cure rate for bovine K. pneumoniae mastitis.

An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies

Escherichia coli is one of the leading causes of bovine mastitis; it can cause sub-clinical, and clinical mastitis characterized by systemic changes, abnormal appearance of milk, and udder inflammation. E. coli pathogenicity in the bovine udder is due to the interaction between its virulence factors and the host factors; it was also linked to the presence of a new pathotype termed mammary pathogenic E. coli (MPEC). However, the presence of this pathotype is commonly debated. Its main virulence factor is the lipopolysaccharide (LPS) that is responsible for causing an endotoxic shock, and inducing a strong immune response by binding to the toll-like receptor 4 (TLR4), and stimulating the expression of chemokines (such as IL-8, and RANTES) and pro-inflammatory cytokines (such as IL-6, and IL-1β). This strong immune response could be used to develop alternative and safe approaches to control E. coli causing bovine mastitis by targeting pro-inflammatory cytokines that can damage the host tissue. The need for alternative treatments against E. coli is due to its ability to resist many conventional antibiotics, which is a huge challenge for curing ill animals. Therefore, the aim of this review was to highlight the pathogenicity of E. coli in the mammary gland, discuss the presence of the new putative pathotype, the mammary pathogenic E. coli (MPEC) pathotype, study the host's immune response, and the alternative treatments that are used against mastitis-associated E. coli.

Antimicrobial Selection for the Treatment of Clinical Mastitis and the Efficacy of Penicillin Treatment Protocols in Large Estonian Dairy Herds

Clinical mastitis (CM) is the most common microbial disease treated in dairy cows. We analyzed the antimicrobial usage in cows with CM (n = 11,420) in large dairy herds (n = 43) in Estonia. CM treatment data were collected during a 12-month study period. The antimicrobial usage was observed during the 21 days from the initiation of treatment, and the incidence of antimicrobial-treated CM was calculated for each study herd. The effect of intramammary (IMM), systemic, and combined (systemic and IMM) penicillin treatment of CM on the post-treatment somatic cell count (SCC) was analyzed using the treatment records of 2222 cows from 24 herds with a mixed multivariable linear regression model. The median incidence of antimicrobial-treated CM was 35.8 per 100 cow-years. Procaine benzylpenicillin and marbofloxacin were used in 6103 (35.5%, 95% CI 34.8-36.2) and 2839 (16.5%, 95% CI 16.0-17.1) CM treatments, respectively. Post-treatment SCC was higher after IMM penicillin therapy compared to systemic or combination therapy. Treatment of CM usually included first-choice antimicrobials, but different antimicrobial combinations were also widely used. The effect of procaine benzylpenicillin to post-treatment SCC was dependent on the administration route, cow parity, and days in milk. Further studies should evaluate the factors affecting veterinarians' choice of antimicrobial used in the treatment of CM.

Systems Biology–Derived Genetic Signatures of Mastitis in Dairy Cattle: A New Avenue for Drug Repurposing

Simple Summary

Therapeutic success of bovine mastitis depends mainly on accurately diagnosing the type of pathogen involved. Despite the development prospects for bovine mastitis diagnosis, including new biomarker discovery to target specific pathogens with high sensitivity and specificity, treatment studies have shown controversial results, and the most efficient, safe, and economical treatments for mastitis are still topics of scientific debate. The goal of this research is the integration of different levels of systems biology data to predict candidate drugs for the control and management of E. coli mastitis. We propose that the novel drugs could be used by pharmaceutical scientists or veterinarians to find commercially efficacious medicines.

Abstract

Mastitis, a disease with high incidence worldwide, is the most prevalent and costly disease in the dairy industry. Gram-negative bacteria such as Escherichia coli (E. coli) are assumed to be among the leading agents causing acute severe infection with clinical signs. E. Coli, environmental mastitis pathogens, are the primary etiological agents of bovine mastitis in well-managed dairy farms. Response to E. Coli infection has a complex pattern affected by genetic and environmental parameters. On the other hand, the efficacy of antibiotics and/or anti-inflammatory treatment in E. coli mastitis is still a topic of scientific debate, and studies on the treatment of clinical cases show conflicting results. Unraveling the bio-signature of mastitis in dairy cattle can open new avenues for drug repurposing. In the current research, a novel, semi-supervised heterogeneous label propagation algorithm named Heter-LP, which applies both local and global network features for data integration, was used to potentially identify novel therapeutic avenues for the treatment of E. coli mastitis. Online data repositories relevant to known diseases, drugs, and gene targets, along with other specialized biological information for E. coli mastitis, including critical genes with robust bio-signatures, drugs, and related disorders, were used as input data for analysis with the Heter-LP algorithm. Our research identified novel drugs such as Glibenclamide, Ipratropium, Salbutamol, and Carbidopa as possible therapeutics that could be used against E. coli mastitis. Predicted relationships can be used by pharmaceutical scientists or veterinarians to find commercially efficacious medicines or a combination of two or more active compounds to treat this infectious disease.

Bacteria Isolated From Milk of Dairy Cows With and Without Clinical Mastitis in Different Regions of Australia and Their AMR Profiles

Mastitis is the most common disease in dairy cattle worldwide. The objectives of this study were to estimate the prevalence of different bacterial species associated with mastitis from dairy herds located in geographically and climatically distinct zones in Australia, and to evaluate the antimicrobial susceptibility of the isolated bacteria. Quarter-level milk samples (n = 419) were collected from 151 mastitis cases and 268 healthy controls originating from 18 dairy herds located in tropical (Northern Queensland), subtropical (Southeast Queensland) and temperate zones (Victoria) between March and June 2019. Milk samples were cultured, and the isolated bacteria were grouped into six groups: Enterobacteriaceae spp.; Streptococcus spp.; Staphylococcus aureus, non-aureus staphylococci (NAS); Bacillus spp.; and Others. Mixed effects conditional logistic regression models were applied to quantify the association between the prevalence of each bacterial group and the herd zone and bulk milk tank somatic cell counts (BMTSCC). Of the 205 isolates, 102 (50%) originated from mastitis cases, and 103 (50%) from controls. Staphylococci were the most prevalent (NAS 32% and S. aureus 11%). Contagious mastitis bacteria were more prevalent in Victoria compared to Queensland dairy herds. NAS species (P < 0.001) were less prevalent in herds with BMTSCC >300,000 cells/mL compared with herds with low BMTSCC ≤150,000 cells/mL. Enterobacteriaceae and Streptococcus spp. groups showed high resistance rates to 1 (51 and 47%, respectively), and 2 (11 and 23%, respectively), antimicrobials. More than one third of the Enterobacteriaceae (48%) and Others (43%) groups spp. were resistant to at least three antimicrobials. This study provided a unique opportunity to investigate the prevalence of mastitis-associated bacteria in clinical cases and in apparently healthy controls. The findings of this study help inform mastitis control and antimicrobial stewardship programs aimed to reduce the prevalence of mastitis and antimicrobial resistance in dairy herds.

Evaluation of a rapid coliform detection kit from clinical mastitis milk using colloidal gold nanoparticle-based immunochromatographic strips

The accurate identification of mastitis‐causing bacteria assists in effective management by both dairy farmers and veterinarians and can be used to implement the selective use of antimicrobials for treatment. The purpose of this study was to evaluate the ability of our developed anti–ribosomal protein-L7/L12 antibody–coated immunochromatographic strip (ICS) test to detect coliforms in milk by comparing the results with the bacteriological culture method. We investigated the performance of the ICS test as compared with the bacteriological culture method using 308 milk samples from clinical bovine mastitis. First, to determine the optimal ICS test cutoff point for detecting coliform mastitis, we developed a receiver-operating characteristic curve. The result showed that the cutoff point was at 0.5 of our index. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value of the ICS test were 81.3%, 84.8%, 69.2%, and 91.54%, respectively. As the clinical signs increased in severity, the F-measure, a weighted harmonic mean of the sensitivity and overall PPV performance, increased. Because it is especially important to treat clinical mastitis appropriately in the early stages of detection, the ICS test, which can be used by both dairy farmers and veterinarians on dairy farms, is considered to be a useful tool for detecting coliform mastitis, which often presents with severe signs.

Effects of Growth Medium and Inoculum Size on Pharmacodynamics Activity of Marbofloxacin against Staphylococcus aureus Isolated from Caprine Clinical Mastitis

Staphylococcus aureus (S. aureus) is an important pathogen that causes clinical mastitis in goats and produces infections difficult to cure. Different antimicrobials as fluoroquinolones have been used against S. aureus. However, the studies developed to evaluate the bacterial drug interaction only have used the MIC as a single reference point with artificial growth media. The aims of this study were to describe the effect of marbofloxacin on S. aureus isolated from mastitis goats' milk by different approaches as the minimum inhibitory and bactericidal concentrations (MIC and MBC) in cation adjusted Mueller-Hinton broth (CAMHB), serum and milk of goats at two inoculum sizes of 10⁵ and 10⁸ CFU/mL, the determination and analysis of the time kill curves (TKC) by non-linear mixed effect models in each growth medium and inoculum size, as well as the estimation of their pharmacokinetics/pharmacodynamics (PK/PD) cutoff values. The results obtained indicate that MIC values were higher and increases 2,4-fold in serum and 3,6-fold in milk at high inoculum, as well as the EC₅₀ values determined by each pharmacodynamics model. Finally, the PK/PD cutoff values defined as fAUC₂₄/MIC ratios to achieve clinical efficacy were highly dependent on inoculum and growth medium, with median values of 60-180, especially at high inoculum in milk, suggesting that further studies are necessary to evaluate and optimize the best therapeutic strategies for treating S. aureus in lactating goats.

Recovery Rates of Treated vs. Non-Treated Dairy Cows with Subclinical Mastitis

The term “spontaneous recovery” refers to a return to a previous condition without any external treatment. In cow mastitis, it refers to cases exhibiting visual symptoms (clinical) or an increase in somatic cell count (SCC) with no visual symptoms (subclinical), with or without identification of a pathogen, from which the animal recovers. A large retrospective analysis of data compiled from the Israeli Dairy Herd Book was performed to evaluate the occurrence of: (i) actual “spontaneous recovery” from the inflammation; (ii) recovery from the inflammation due to antibiotic treatment. In 2018, 123,958 cows from 650 herds with first elevation of SCC at monthly test-day milk yield were clustered into five SCC-cutoff levels (CL) (×103 cells/mL): CL1 (200–299), CL2 (300–399), CL3 (400–499), CL4 (500–999), CL5 (≥1000). Each cutoff level was analyzed separately, and each cow appeared only once in the same lactation and cutoff level, thus resulting in five independent analyses. Recovery was defined as decreased SCC on all three monthly test days, or on the second and third test days, set to: R1 (<100 × 103 cells/mL); R2 (<250 × 103 cells/mL). No difference was found among cutoff levels when the recovery was set to R1, with only 10–12% of the cows presenting spontaneous recovery. When the recovery was set to R2, percent spontaneous recovery was 25–27% at the three higher cutoff levels (CL3–CL5) and 35–41% at the lowest levels (CL1, CL2). Antibiotic treatment was administered to only ~10% of the cows, and in only the higher cutoff-level groups—CL4 and CL5. No difference was found between spontaneous recovery and recovery after antibiotic treatment. Moreover, percentage culled cows treated with antibiotics was significantly higher (p < 0.01) than that of non-treated culled cows (18 and 10.2, respectively), suggesting that the more severe mastitis cases were treated. We concluded that (i) actual spontaneous recovery from inflammation is low and does not depend on the number of cells in the milk at time of infection, and (ii) recovery from inflammation following antibiotic treatment is not higher.

Molecular characteristics of Escherichia coli from bulk tank milk in Korea

Background

Escherichia coli, which causes subclinical or clinical mastitis in cattle, is responsible for transmitting antimicrobial resistance via human consumption of raw milk or raw milk products.

Objectives

The objective of this study was to investigate the molecular characteristics of 183 E. coli from bulk tank milk of five different dairy factories in Korea.

Methods

The molecular characteristics of E. coli such as serogroup, virulence, antimicrobial resistance, and integron genes were detected using polymerase chain reaction and antimicrobial susceptibility were tested using the disk diffusion test.

Results

In the distribution of phylogenetic groups, group D was the most prevalent (59.6%) and followed by group B1 (25.1%). The most predominant serogroup was O173 (15.3%), and a total of 46 different serotypes were detected. The virulence gene found most often was fimH (73.2%), and stx1, fimH, incC, fyuA, and iutA genes were significantly higher in isolates of phylogenetic group B1 compared to phylogenetic groups A, B2, and D (p < 0.05). Among 64 E. coli isolates that showed resistance to at least one antimicrobial, the highest resistance rate was observed for tetracyclines (37.5%). All 18 integron-positive E. coli carried the integron class I (int1) gene, and three different gene cassette arrangements, dfrA12+aadA2 (2 isolates), aac(6′)-Ib3+aac(6′)-Ib-cr+aadA4 (2 isolates), and dfrA17+aadA5 (1 isolate) were detected.

Conclusions

These data suggest that the E. coli from bulk tank milk can be an indicator for dissemination of antimicrobial resistance and virulence factors via cross-contamination.

Characterisation of Early Positive mcr-1 Resistance Gene and Plasmidome in Escherichia coli Pathogenic Strains Associated with Variable Phylogroups under Colistin Selection

An antibiotic susceptibility monitoring programme was conducted from 2004 to 2010, resulting in a collection of 143 Escherichia coli cultured from bovine faecal samples (diarrhoea) and milk-aliquots (mastitis). The isolates were subjected to whole-genome sequencing and were distributed in phylogroups A, B1, B2, C, D, E, and G with no correlation for particular genotypes with pathotypes. In fact, the population structure showed that the strains belonging to the different phylogroups matched broadly to ST complexes; however, the isolates are randomly associated with the diseases, highlighting the necessity to investigate the virulence factors more accurately in order to identify the mechanisms by which they cause disease. The antimicrobial resistance was assessed phenotypically, confirming the genomic prediction on three isolates that were resistant to colistin, although one isolate was positive for the presence of the gene mcr-1 but susceptible to colistin. To further characterise the genomic context, the four strains were sequenced by using a single-molecule long read approach. Genetic analyses indicated that these four isolates harboured complex and diverse plasmids encoding not only antibiotic resistant genes (including mcr-1 and bla) but also virulence genes (siderophore, ColV, T4SS). A detailed description of the plasmids of these four E. coli strains, which are linked to bovine mastitis and diarrhoea, is presented for the first time along with the characterisation of the predicted antibiotic resistance genes. The study highlighted the diversity of incompatibility types encoding complex antibiotic resistance elements such as Tn6330, ISEcp1, Tn6029, and IS5075. The mcr-1 resistance determinant was identified in IncHI2 plasmids pCFS3273-1 and pCFS3292-1, thus providing some of the earliest examples of mcr-1 reported in Europe, and these sequences may be a representative of the early mcr-1 plasmidome characterisation in the EU/EEA.

Evidence-Based Tracking of MDR E. coli from Bovine Endometritis and Its Elimination by Effective Novel Therapeutics

Antibiotic-resistant bacteria have become the predominant etiology of endometritis and thus require effective treatment approaches. We used ultrasonography coupled with clinical signs and presented complaints of reproductive issues to investigate the epidemiology, phylogenetic analysis, antimicrobial resistance, and development of novel therapeutics against Escherichia coli isolated from endometritis in bovine (n = 304 from 10 commercial dairy farms). The prevalence of bovine endometritis in this study was 43.75%, while among these, 72.18% samples were positive for E. coli. Nucleotide analysis performed through BLAST and MEGAX showed 98% similarity to the nucleotide sequence of the reference E. coli strain (accession number CP067311.1). The disk diffusion assay revealed pathogen resistance to most antibiotics. Pattern of MIC order of resistance was as follows: enrofloxacin < gentamicin < co-amoxiclav < streptomycin < amoxicillin < metronidazole < oxytetracycline. Field trials revealed the highest recovery rate (in terms of clearance of endometritis and establishment of pregnancy) in case of gentamicin + enrofloxacin (100%) and gentamicin alone (100%), followed by co-amoxiclav + gentamicin (84.61%), oxytetracycline alone (78.57%), and metronidazole + enrofloxacin (33.33%). Hence, the current study reported a higher prevalence of multidrug-resistant E. coli showing considerable similarity with reference strain, and finally, the effective response of novel antibiotics to treat cases.

Indications for the use of highest priority critically important antimicrobials in the veterinary sector

BACKGROUND

Among the measures taken to preserve the clinical efficacy of highest priority critically important antimicrobials (HP-CIAs), the WHO has recommended avoiding their use in food-producing animals. Little is known regarding the indications for which different antimicrobial classes are used in animals, even in countries where data on antimicrobial use are available.

OBJECTIVES

To outline, in a narrative review, the diseases for which HP-CIAs are used in veterinary medicine, highlighting incongruences with international guidelines and disease conditions where effective alternatives to HP-CIAs are missing.

METHODS

Scientific literature, national reports and expert opinion were used to describe the indications for the use of HP-CIAs in the main food-producing (pigs, cattle and poultry) and companion (horses, dogs and cats) animal species.

RESULTS

The most common indications for use of HP-CIAs are enteric and respiratory infections in pigs, cattle and poultry, urogenital infections in dogs and cats and respiratory infections in horses. In some instances, no valid and convenient alternatives to colistin and macrolides are available against certain porcine enteric and bovine respiratory pathogens. Effective, legal and convenient alternatives to HP-CIAs are also lacking for managing common infections in cats, for which oral administration is difficult, Rhodococcus equi infections in horses, some enteric and respiratory infections in poultry and MDR infections in all companion animal species.

CONCLUSIONS

Future research and stewardship programmes should focus on the disease conditions identified by this review to reduce the use of HP-CIAs in the veterinary sector.

Advances in therapeutic and managemental approaches of bovine mastitis: a comprehensive review

Mastitis (intramammary inflammation) caused by infectious pathogens is still considered a devastating condition of dairy animals affecting animal welfare as well as economically incurring huge losses to the dairy industry by means of decreased production performance and increased culling rates. Bovine mastitis is the inflammation of the mammary glands/udder of bovines, caused by bacterial pathogens, in most cases. Routine diagnosis is based on clinical and subclinical forms of the disease. This underlines the significance of early and rapid identification/detection of etiological agents at the farm level, for which several diagnostic techniques have been developed. Therapeutic regimens such as antibiotics, immunotherapy, bacteriocins, bacteriophages, antimicrobial peptides, probiotics, stem cell therapy, native secretory factors, nutritional, dry cow and lactation therapy, genetic selection, herbs, and nanoparticle technology-based therapy have been evaluated for their efficacy in the treatment of mastitis. Even though several strategies have been developed over the years for the purpose of managing both clinical and subclinical forms of mastitis, all of them lacked the efficacy to eliminate the associated etiological agent when used as a monotherapy. Further, research has to be directed towards the development of new therapeutic agents/techniques that can both replace conventional techniques and also solve the problem of emerging antibiotic resistance. The objective of the present review is to describe the etiological agents, pathogenesis, and diagnosis in brief along with an extensive discussion on the advances in the treatment and management of mastitis, which would help safeguard the health of dairy animals.

Biofilm Research in Bovine Mastitis

Bovine mastitis is one of the most important diseases in the dairy industry and has detrimental impact on the economy and welfare of the animals. Further, treatment failure results in increased antibiotic use in the dairy industry, as some of these mastitis cases for unknown reasons are not resolved despite standard antibiotic treatment. Chronic biofilm infections are notoriously known to be difficult to eradicate with antibiotics and biofilm formation could be a possible explanation for mastitis cases that are not resolved by standard treatment. This paper reviews the current literature on biofilm in bovine mastitis research to evaluate the status and methods used in the literature. Focus of the current research has been on isolates from milk samples and investigation of their biofilm forming properties in vitro. However, in vitro observations of biofilm formation are not easily comparable with the in vivo situation inside the udder. Only two papers investigate the location and distribution of bacterial biofilms inside udders of dairy cows with mastitis. Based on the current knowledge, the role of biofilm in bovine mastitis is still unclear and more in vivo investigations are needed to uncover the actual role of biofilm formation in the pathogenesis of bovine mastitis.

Evolution of honey resistance in experimental populations of bacteria depends on the type of honey and has no major side effects for antibiotic susceptibility

With rising antibiotic resistance, alternative treatments for communicable diseases are increasingly relevant. One possible alternative for some types of infections is honey, used in wound care since before 2000 BCE and more recently in licensed, medical-grade products. However, it is unclear whether medical application of honey results in the evolution of bacterial honey resistance and whether this has collateral effects on other bacterial traits such as antibiotic resistance. Here, we used single-step screening assays and serial transfer at increasing concentrations to isolate honey-resistant mutants of Escherichia coli. We only detected bacteria with consistently increased resistance to the honey they evolved in for two of the four tested honey products, and the observed increases were small (maximum twofold increase in IC90). Genomic sequencing and experiments with single-gene knockouts showed a key mechanism by which bacteria increased their honey resistance was by mutating genes involved in detoxifying methylglyoxal, which contributes to the antibacterial activity of Leptospermum honeys. Crucially, we found no evidence that honey adaptation conferred cross-resistance or collateral sensitivity against nine antibiotics from six different classes. These results reveal constraints on bacterial adaptation to different types of honey, improving our ability to predict downstream consequences of wider honey application in medicine.

Prevalence and risk factors for multidrug-resistant Escherichia coli isolated from subclinical mastitis in the western Chitwan region of Nepal

Subclinical mastitis (SCM) represents a significant burden and challenge to modern dairy management. Multidrug-resistant Escherichia coli (MDR E. coli) in milk poses a public health threat to humans especially via the consumption of unpasteurized dairy products. This study aimed to determine the occurrence of MDR E. coli in cows and buffalo in the households of the western part of the Chitwan district of Nepal. A total of 243 lactating cows and buffalo were included in this study. Milk samples (n = 972) were screened using the California Mastitis Test (CMT). The E. coli was isolated from milk samples that were positive for CMT using standard bacteriological protocols. A semi-structured questionnaire was administered to farmers to identify the risk factors associated with the occurrence of SCM in cows and buffalo. Of the 243 dairy animals screened, 42.8% (n = 104/243) showed positive CMT results. However, of the 972 quarters sampled, only 19.3% (n = 188/972) were positive for SCM. The prevalence of E. coli in these animals was found to be 16.5% in animals (n = 40/243). However, E. coli was isolated from only 5% (n = 49/972) of the quarters. Of the 49 E. coli isolated, the resistance to ceftriaxone (38.8%, n = 19/49) and ciprofloxacin (37.7%, n = 17/49) were the most prevalent. Animals with a history of mastitis were 3.57 times more likely to have SCM than other animals. Similarly, lactating animals with previous teat abrasions were 3.22 times more likely to develop SCM than animals without teat injuries. As expected, cleaning the barn once in 2 to 3 d was associated with an increased occurrence of SCM in lactating cows. This study reports the occurrence of MDR E. coli in SCM, which poses a public health threat. Creating awareness of milk pasteurization, and food safety practices are necessary among the farmers.

Veterinary Treatment Approach and Antibiotic Usage for Clinical Mastitis in Danish Dairy Herds

Danish veterinarians’ treatment approach and use of antibiotics for clinical mastitis were investigated through a web-based questionnaire. The objective of the study was to describe and evaluate how the clinical mastitis treatment practice in Danish dairy herds corresponds to evidence from the literature and legislative requirements, in order to suggest directions for improvements and approaches encouraging the prudent use of antibiotics. In total, 174 veterinarians working with cattle received the questionnaire and 85 (48.9%) completed it. Their answers suggested that the Danish treatment approach for clinical mastitis generally relies on combined systemic and intramammary antibiotic administration (92% would use this often or always) and almost always includes supportive treatment with nonsteroidal anti-inflammatory drugs (99% would use it often or always in combination with antibiotic therapy). While collecting milk samples in order to target treatment towards pathogens is a priority in the legislation and for veterinarians, the direct application seems hindered due to the waiting time with the currently used analysis practice. Consequently, 91% reported that they would start treatment immediately after clinical examination often or always. The results of this investigation show that there is a potential for improvement in targeting treatments towards the causative pathogen by encouraging methods that allow for a more rapid reliable pathogen determination. When this issue has been addressed, the available evidence on the best treatment practice of Gram-negative-caused mastitis cases can be applied properly, reducing the volume of antibiotic treatments with limited expected effect. Additionally, investigating the potential of reducing combined administration to only intramammary treatment in Gram-positive cases could be a further step towards a more prudent antibiotic strategy.

Are Severe Mastitis Cases in Dairy Cows Associated with Bacteremia?

The objective of this study was to investigate the occurrence of bacteremia in dairy cows with severe mastitis. Milk samples were collected from affected udder quarters, and corresponding blood samples were collected from dairy cows with severe mastitis at the time of diagnosis before any therapeutic measures were undertaken. The cultural detection of pathogens in blood classified a bacteremia. Further diagnostic tests were performed to provide evidence of bacteremia. This was realized by PCR with regard to S. aureus, E. coli and S. uberis and the Limulus test. Detection of culturable pathogens in the blood of cows with severe clinical mastitis was rare and occurred in only one of 70 (1.4%) cases. Overall, bacterial growth was detected in 53 of 70 (75.7%) milk samples. S. uberis (22/70), E. coli (12/70) and S. aureus (4/70) were the most frequently isolated pathogens from milk of cows with severe mastitis. PCR was performed in 38 of 70 (54.3%) blood samples. PCR was positive in eight of 38 cases. S. uberis was found most frequently in six blood samples (8.6%). E. coli was found on PCR in one blood sample (1.4%). S. aureus was identified in one blood sample (1.4%). When Coliforms were detected in the quarter milk sample, a Limulus test was performed in the corresponding blood sample. In three of 15 cases, the Limulus test was positive (4.3% of samples). Further studies are needed to investigate the occurrence of bacteremia in cows with severe mastitis in a higher population size.

What Is Success? A Narrative Review of Research Evaluating Outcomes of Antibiotics Used for Treatment of Clinical Mastitis

Treatment of clinical mastitis is the most common reason that antimicrobials are given to adult dairy cows and careful consideration of treatment protocols is necessary to ensure responsible antimicrobial stewardship. Clinical mastitis is caused by a variety of bacteria which stimulate an immune response that often results in spontaneous bacteriological clearance but can develop into long-term subclinical infections. Use of antimicrobial therapy is most beneficial for cases that are caused by pathogens that have a low rate of spontaneous cure but high rate of therapeutic cure. The purpose of this paper is to review studies that evaluated outcomes of antimicrobial therapy of clinical mastitis. Few studies reported differences in bacteriological cure among treatments and this outcome was rarely associated with clinical outcomes. Return to normal milk appearance was evaluated in most studies but demonstrated little variation and is not a reliable indicator of therapeutic success. Somatic cell count should be measured at quarter-level and will decline gradually after bacteriological clearance. Few researchers have evaluated important clinical outcomes such as post-treatment milk yield or culling. Few differences among approved antimicrobial therapies have been demonstrated and selection of antimicrobial therapy should consider the spectrum of activity relative to etiology.