Characterization of Staphylococcus Species Isolated from Bovine Quarter Milk Samples

Changes in antimicrobial resistance of Staphylococcus aureus in bovine quarter milk samples from southern Germany between 2012 and 2022

The objective of this study was to describe the in vitro resistance of Staphylococcus aureus from bovine quarter milk samples obtained by the udder health laboratory of the Bavarian Animal Health Services between 2012 and 2022. All S. aureus samples were tested for β-lactamase production and only forwarded to further microbroth susceptibility testing either if the β-lactamase result was positive or upon explicit request by the submitter. The growth of most S. aureus isolates was inhibited at the lowest evaluated minimum inhibitory concentration (MIC) of tested antimicrobials, with the MIC50 and MIC90 (the MIC where 50% and 90% of isolates were inhibited by the tested antibiotics, respectively) mostly beneath the respective breakpoint. On average, about one-fourth (24%, n = 5,718) of tested isolates was resistant to erythromycin. However, the prevalence of resistant isolates dropped from 53% (n = 1,018) in 2012 to 8% (n = 113) in 2022. The second highest prevalence of in vitro resistance was to penicillin (17%, of all isolates tested for β-lactamase production, n = 28,069). Less than 14% of isolates were resistant to the remaining assessed antimicrobial agents (cefoperazone, pirlimycin, kanamycin-cefalexin, marbofloxacin, amoxicillin-clavulanate, cefquinome, or cefazolin, respectively). Over the years, 4% (n = 959) of the S. aureus isolates selected for microbroth susceptibility testing (and 0.8% (n = 1,392) of all submitted S. aureus isolates) were methicillin-resistant S. aureus, and 5% (n = 1,162) of S. aureus isolates were multidrug resistant. However, there was an overall trend toward fewer resistant isolates. These findings are consistent with those of several European monitoring programs that reported a slight decrease of antimicrobial resistance (AMR) of bovine S. aureus in countries where antibiotic use in veterinary medicine was reduced. Notably, isolates of clinical mastitis cases were consistently less likely to express in vitro resistance than isolates obtained from milk of healthy cows or subclinical mastitis cases. In conclusion, AMR of S. aureus was decreasing and penicillin should remain the first-choice antimicrobial in the attempt of treating S. aureus intramammary infections in Bavaria.

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

Detection of Staphylococcus Isolates and Their Antimicrobial Resistance Profiles and Virulence Genes from Subclinical Mastitis Cattle Milk Using MALDI-TOF MS, PCR and Sequencing in Free State Province, South Africa

Staphylococcus species are amongst the bacteria that cause bovine mastitis worldwide, whereby they produce a wide range of protein toxins, virulence factors, and antimicrobial-resistant properties which are enhancing the pathogenicity of these organisms. This study aimed to detect Staphylococcus spp. from the milk of cattle with subclinical mastitis using MALDI-TOF MS and 16S rRNA PCR as well as screening for antimicrobial resistance (AMR) and virulence genes. Our results uncovered that from 166 sampled cows, only 33.13% had subclinical mastitis after initial screening, while the quarter-level prevalence was 54%. Of the 50 cultured bacterial isolates, MALDI-TOF MS and 16S rRNA PCR assay and sequencing identified S. aureus as the dominant bacteria by 76%. Furthermore, an AMR susceptibility test showed that 86% of the isolates were resistant to penicillin, followed by ciprofloxacin (80%) and cefoxitin (52%). Antimicrobial resistance and virulence genes showed that 16% of the isolates carried the mecA gene, while 52% of the isolates carried the Lg G-binding region gene, followed by coa (42%), spa (40%), hla (38%), and hlb (38%), whereas sea and bap genes were detected in 10% and 2% of the isolates, respectively. The occurrence of virulence factors and antimicrobial resistance profiles highlights the need for appropriate strategies to control the spread of these pathogens.

Molecular epidemiology and characterization of antimicrobial-resistant Staphylococcus haemolyticus strains isolated from dairy cattle milk in Northwest, China

Introduction

Non-aureus Staphylococcus (NAS) species are currently the most commonly identified microbial agents causing sub-clinical infections of the udder and are also deemed as opportunistic pathogens of clinical mastitis in dairy cattle. More than 10 NAS species have been identified and studied but little is known about S. haemolyticus in accordance with dairy mastitis. The present study focused on the molecular epidemiology and genotypic characterization of S. haemolyticus isolated from dairy cattle milk in Northwest, China.

Methods

In this study, a total of 356 milk samples were collected from large dairy farms in three provinces in Northwest, China. The bacterial isolation and presumptive identification were done by microbiological and biochemical methods following the molecular confirmation by 16S rRNA gene sequencing. The antimicrobial susceptibility testing (AST) was done by Kirby-Bauer disk diffusion assay and antibiotic-resistance genes (ARGs) were identified by PCR. The phylogenetic grouping and sequence typing was done by Pulsed Field Gel Electrophoresis (PFGE) and Multi-Locus Sequence Typing (MLST) respectively.

Results

In total, 39/356 (11.0%) were identified as positive for S. haemolyticus. The overall prevalence of other Staphylococcus species was noted to be 39.6% (141/356), while the species distribution was as follows: S. aureus 14.9%, S. sciuri 10.4%, S. saprophyticus 7.6%, S. chromogenes 4.2%, S. simulans 1.4%, and S. epidermidis 1.1%. The antimicrobial susceptibility of 39 S. haemolyticus strains exhibited higher resistance to erythromycin (92.3%) followed by trimethoprim-sulfamethoxazole (51.3%), ciprofloxacin (43.6%), florfenicol (30.8%), cefoxitin (28.2%), and gentamicin (23.1%). All of the S. haemolyticus strains were susceptible to tetracycline, vancomycin, and linezolid. The overall percentage of multi-drug resistant (MDR) S. haemolyticus strains was noted to be 46.15% (18/39). Among ARGs, mphC was identified as predominant (82.05%), followed by ermB (33.33%), floR (30.77%), gyrA (30.77%), sul1 (28.21%), ermA (23.08%), aadD (12.82%), grlA (12.82%), aacA-aphD (10.26%), sul2 (10.26%), dfrA (7.69%), and dfrG (5.13%). The PFGE categorized 39 S. haemolyticus strains into A-H phylogenetic groups while the MLST categorized strains into eight STs with ST8 being the most predominant while other STs identified were ST3, ST11, ST22, ST32, ST19, ST16, and ST7.

Conclusion

These findings provided new insights into our understanding of the epidemiology and genetic characteristics of S. haemolyticus in dairy farms to inform interventions limiting the spread of AMR in dairy production.

A framework for evaluation of on-farm mastitis diagnostics in Australia

Numerous culture-based diagnostics are available on the Australian and international markets for on-farm detection of bacterial pathogens in milk. Use of such diagnostics may provide an opportunity to improve the prudent use of antimicrobials in udder health management. Farms are low-resource settings in terms of diagnostic microbiology capacity. The World Health Organisation has identified criteria for the evaluation of diagnostic tests in low resource settings based on Accuracy, Sensitivity, Specificity, User-friendliness, being Rapid or Robust, Equipment-free and being Deliverable (ASSURED). Here, we review how those criteria can be interpreted in the context of microbiological diagnosis of mastitis pathogens, and how on-farm diagnostics that are currently available in Australia perform relative to ASSURED criteria. This evaluation identifies multiple trade-offs, both with regard to scientific criteria and with regards to convenience criteria. More importantly, the purpose of testing may differ between farms, and test performance should be evaluated relative to its intended use. The ability of on-farm mastitis diagnostics to inform mastitis treatment decision-making in a timely and cost-effective manner depends not just on test characteristics but also on farm-specific pathogen prevalence, and on the farm enterprise's priorities and the farm manager's potential courses of action. With most assay evaluations to date conducted in professional laboratories, there is a surprising dearth of information on how well any of the diagnostic tests perform on-farm and, indeed, of the on-farm decision-making processes that they aim to inform.

Invited review: Antimicrobial resistance in bovine mastitis pathogens: A review of genetic determinants and prevalence of resistance in European countries

Antimicrobial resistance is an urgent and growing problem worldwide, both for human and animal health. In the animal health sector actions have been taken as concerns grow regarding the development and spread of antimicrobial resistance. Mastitis is the most common infection in dairy cattle. We aimed to summarize the genetic determinants found in staphylococci, streptococci, and Enterobacteriaceae isolated from mastitic milk samples and provide a comparison of percentage resistance to a variety of antimicrobials in European countries.

Proteomics approaches: A review regarding an importance of proteome analyses in understanding the pathogens and diseases

Proteomics is playing an increasingly important role in identifying pathogens, emerging and re-emerging infectious agents, understanding pathogenesis, and diagnosis of diseases. Recently, more advanced and sophisticated proteomics technologies have transformed disease diagnostics and vaccines development. The detection of pathogens is made possible by more accurate and time-constrained technologies, resulting in an early diagnosis. More detailed and comprehensive information regarding the proteome of any noxious agent is made possible by combining mass spectrometry with various gel-based or short-gun proteomics approaches recently. MALDI-ToF has been proved quite useful in identifying and distinguishing bacterial pathogens. Other quantitative approaches are doing their best to investigate bacterial virulent factors, diagnostic markers and vaccine candidates. Proteomics is also helping in the identification of secreted proteins and their virulence-related functions. This review aims to highlight the role of cutting-edge proteomics approaches in better understanding the functional genomics of pathogens. This also underlines the limitations of proteomics in bacterial secretome research.

May Sulfonamide Inhibitors of Carbonic Anhydrases from Mammaliicoccus sciuri Prevent Antimicrobial Resistance Due to Gene Transfer to Other Harmful Staphylococci?

Mammaliicoccus sciuri, previously known as Staphylococcus sciuri, is a Gram-positive bacterium involved in gene transfer phenomena that confer resistance to multiple antibiotics. These plasmid-encoded genes can be easily transferred to other pathogenic staphylococci. Because antibiotic resistance is rising, inhibiting M. sciuri proliferation may be a credible strategy for restricting antimicrobial resistance gene transfer to other pathogenic bacteria. Recently, it has been shown that blocking bacterial carbonic anhydrases (CAs, EC 4.2.1.1), metalloenzymes sustaining bacterial metabolic activities, can reduce pathogen survival and fitness. Here, the recombinant M. sciuri γ-CA (MscCAγ) has been cloned and purified, utilizing the DNA recombinant technology. Its kinetic properties for the CO₂ hydration reaction, as well as the sulfonamide inhibition profile, were investigated and compared with those reported earlier for MscCAβ (previously described as SauBCA) and the two off-target human CA isoforms (hCA I and hCA II). The recombinant MscCAγ showed significant hydratase activity. Moreover, the MscCAγ sulfonamide inhibitory profile was different from that of MscCAβ, implying that a varied amino acid set typifies the catalytic pocket of the two enzymes. These differences provide additional evidence for the possibility of developing novel CA class-specific inhibitors.

Quantifying current and future raw milk losses due to bovine mastitis on European dairy farms under climate change scenarios

Bovine mastitis is an infectious disease that causes udder inflammation and is responsible for raw milk losses across European dairy farms. It is associated with reduced cow milk yield and contributes to elevated Somatic Cell Count (SCC) in raw milk. Staphylococcus aureus is one of the most prevalent mastitis pathogens that cause subclinical and clinical mastitis and can be present as a coloniser bacterium in cows. Climate change and geographical variability may influence the prevalence of this pathogen. Thus, this research aimed to predict the raw milk losses in three major dairy-producing regions across Europe (i.e. Mediterranean, Atlantic and Continental) under climate change scenarios. An exposure assessment model and a stepwise probabilistic model were developed to predict potential cow milk yield reduction, S. aureus and SCC concentrations in the bulk tank milk at dairy farms. Baseline (i.e. present) and future climate change scenarios were defined, and the resultant concentrations of SCC and S. aureus were compared to the actual European regulatory limits. Across the three regions, raw milk losses ranged from 1.06% to 2.15% in the baseline. However, they increased up to 3.21% in the climate change scenarios when no on-farm improvements were considered. Regarding geographical variation, the highest potential milk losses were reported for the Mediterranean and the lowest for the Continental region. Concerning the fulfilment of the regulatory limits, the mean of S. aureus and SCC levels in milk did not exceed them either in any region or scenario. Nevertheless, when looking at percentiles, the 10th percentile remained above the limits of S. aureus in Atlantic and Mediterranean, but not in the Continental region. The findings provide a snapshot of climate change impacts on raw milk losses due to mastitis. They will allow farmers to detect weaknesses and prepare them to develop adaptation plans to climate change.

Etiology of Mastitis and Antimicrobial Resistance in Dairy Cattle Farms in the Western Part of Romania

The present study aimed to determine the bacteria isolated from bovine mastitis and their antimicrobial resistance in the western part of Romania. Clinical mastitis was diagnosed based on local inflammation in the udder, changes in milk, and when present, generalized symptoms. Subclinical mastitis was assessed using a rapid test—the California Mastitis Test. The identification of bacterial strains was performed based on biochemical profiles using API system tests (API 20 E, API Staph, API 20 Strep, API Coryne, API 20 NE (bioMerieux, Marcy l’Etoile, France), and MALDI-TOF mass spectrometry (MS). The prevalent isolated bacteria were Staphylococcus spp. (50/116; 43.19%), followed by Streptococcus spp. (26/116; 22.41%), E. coli (16/116; 13.79%), Corynebacterium spp. (9/116; 7.75%), Enterococcus spp. (10/116; 8.62%), and Enterobacter spp. (5/116; 4.31%). Phenotype antimicrobial resistance profiling was performed used the disc diffusion method. Generally, Gram-positive bacteria showed low susceptibility to most of the antimicrobials tested, except cephalothin. Susceptibilities to penicillins and quinolones were fairly high in Gram-negative bacteria, whereas resistance was observed to macrolides, aminoglycosides, and tetracyclines. The highest number of isolates were multidrug resistant (MDR), the resistance pathotypes identified including the most frequently antimicrobials used in cow mastitis treatment in Romania.

Assessment of animal diseases caused by bacteria resistant to antimicrobials: cattle

In this opinion, the antimicrobial resistant bacteria responsible for transmissible diseases that constitute a threat to the health of cattle have been assessed. The assessment has been performed following a methodology based on information collected by an extensive literature review and expert judgement. Details of the methodology used for this assessment are explained in a separate opinion. A global state of play on antimicrobial resistance in clinical isolates of Escherichia coli (non-VTEC), Klebsiella pneumoniae, Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Mycoplasma bovis, Moraxella bovis, Fusobacterium necrophorum and Trueperella pyogenes is provided. Among those bacteria, EFSA identified E. coli and S. aureus with ≥ 66% certainty as being the most relevant antimicrobial resistant bacteria in cattle in the EU based on the available evidence. The animal health impact of these most relevant bacteria, as well as their eligibility for being listed and categorised within the animal health law framework will be assessed in separate scientific opinions.

Genomic comparisons and phylogenetic analysis of mastitis-related staphylococci with a focus on adhesion, biofilm, and related regulatory genes

Mastitis is a common and costly disease on dairy farms, commonly caused by Staphylococcus spp. though the various species are associated with different clinical outcomes. In the current study, we performed genomic analyses to determine the prevalence of adhesion, biofilm, and related regulatory genes in 478 staphylococcal species isolated from clinical and subclinical mastitis cases deposited in public databases. The most prevalent adhesin genes (ebpS, atl, pls, sasH and sasF) were found in both clinical and subclinical isolates. However, the ebpS gene was absent in subclinical isolates of Staphylococcus arlettae, S. succinus, S. sciuri, S. equorun, S. galinarum, and S. saprophyticus. In contrast, the coa, eap, emp, efb, and vWbp genes were present more frequently in clinical (vs. subclincal) mastitis isolates and were highly correlated with the presence of the biofim operon (icaABCD) and its transcriptional regulator, icaR. Co-phylogenetic analyses suggested that many of these adhesins, biofilm, and associated regulatory genes could have been horizontally disseminated between clinical and subclinical isolates. Our results further suggest that several adhesins, biofilm, and related regulatory genes, which have been overlooked in previous studies, may be of use for virulence profiling of mastitis-related Staphylococcus strains or as potential targets for vaccine development.

The relationship of bovine milk somatic cell count to neutrophil level in samples of cow's milk assessed by an automatic cell counter

This research communication describes the application of a fluorescent automatic cell counter Lactoscan SCC for simultaneous determination of somatic cell count and neutrophils in bovine milk. The obtained results were compared with results obtained by a flow cytometer and a light microscope. The Pearson correlations between the methods were calculated. A comparison between the main characteristics of the three kinds of analysis was made - the assay duration and the intra-assay precision. A relation between the SCC and neutrophil cells was observed in 55 milk samples. The obtained results confirm that the simultaneous determination of SCC and neutrophil analysis are necessary and support the early diagnosis of mastitis, the timely treatment of the animal and the avoidance of major economic losses.

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.

Non-aureus Staphylococci and Bovine Udder Health: Current Understanding and Knowledge Gaps

Despite considerable efforts to control bovine mastitis and explain its causes, it remains the most costly and common disease of dairy cattle worldwide. The role and impact of non-aureus staphylococci (NAS) in udder health are not entirely understood. These Gram-positive bacteria have become the most frequently isolated group of bacteria in milk samples of dairy cows and are associated with (mild) clinical and subclinical mastitis. Different species and strains of NAS differ in their epidemiology, pathogenicity, virulence, ecology and host adaptation, and antimicrobial resistance profiles. They have distinct relationships with the microbiome composition of the udder and may also have protective effects against other mastitis pathogens. Some appear to persist on the skin and in the teat canal and udder, while others seem to be transient residents of the udder from the environment. Analyzing genotypic and phenotypic differences in individual species may also hold clues to why some appear more successful than others in colonizing the udder. Understanding species-level interactions within the microbiome and its interactions with host genetics will clarify the role of NAS in bovine mastitis and udder health.

Heat stress and cow factors affect bacteria shedding pattern from naturally infected mammary gland quarters in dairy cattle

Mastitis-causing pathogens are shed from infected mammary gland quarters and thus contribute to an increased risk of new intramammary infections. The objective of the current study was to investigate the shedding characteristics of various mastitis-causing pathogens and associated animal-specific (somatic cell score and parity) and environmental (heat stress) factors. In a longitudinal study, infected udder quarters were sampled consecutively on 5 dairy farms in Germany. To capture climatic factors, temperature-humidity index (THI) was calculated. In the laboratory analysis, the pathogens and their counts in the milk samples were determined. A generalized linear mixed model with gamma link was used to evaluate the factors influencing pathogen-shedding characteristics. The variables somatic cell count, pathogen, parity, and THI had significant influence on pathogen shedding. Staphylococci were shed in lower values than streptococci. The pathogen shedding from mammary gland quarters with intramammary infections was higher in the first and second lactation than in higher lactations. Exceeding the THI threshold 60 resulted in higher pathogen counts on the same day. This was only caused by the pathogens yeasts and Streptococcus uberis. Possible mechanisms causing differences in pathogen shedding are changes in the counts due to influenced milk quantities, better growth conditions at higher temperatures, or altered immunological reactions. The mechanisms often remain speculative and require further investigation. The study underlines the contribution of cows with high somatic cell counts regarding the transmission of mastitis pathogens within a herd. Furthermore, it becomes clear that heat stress in Germany influences udder health and that prevention measures are useful.

Efficacy of Natural Formulations in Bovine Mastitis Pathology: Alternative Solution to Antibiotic Treatment

Introduction

Bovine mastitis is an inflammatory disease of the udder that causes important economic losses in the animal breeding and dairy product industries. Nowadays, the conventional livestock antibiotic treatments are slowly being replaced by alternative treatments. In this context, the main aim of this study was to evaluate the efficacy of natural products in alternative treatment of bovine mastitis.

Material and Methods

Two natural formulations with previously suggested in vitro antimicrobial effect were tested in vivo on mastitic cows. Animals with a positive diagnosis for mastitis (n = 20) were divided into three treatment groups: two groups (n = 8) were administered formulations of propolis, alcoholic extracts of Brewers Gold and Perle hops, plum lichen, common mallow, marigold, absinthe wormwood, black poplar buds, lemon balm, and essential oils of oregano, lavender, and rosemary designated R4 and R7 (differing only in the latter being more concentrated) and one group (n = 4) a conventional antibiotic mixture. In vivo efficacy of treatments was evaluated by somatic cell and standard plate counts, the treatment being considered efficacious when both parameters were under the maximum limit.

Results

R7 was effective in the most cases, being therapeutically bactericidal in six out of eight cows, while R4 gave good results in three out of eight cows, and conventional antibiotics cured one out of four.

Conclusion

These results suggest the possible therapeutic potential of these natural products in bovine mastitis.

Differentiation of non-aureus staphylococci species isolated from bovine mastitis by PCR-RFLP of groEL and gap genes in comparison to MALDI-TOF mass spectrometry

Intramammary infections (IMI) cause serious economic losses for farmers and the dairy industry. Cases of subclinical mastitis are commonly the result of infection by minor pathogens such as non-aureus staphylococci (NAS), so their correct identification is important for appropriate therapeutic intervention and management. The aim of this study was to assess the reliability of PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) of the groEL and gap genes to discriminate between bovine-associated NAS species, using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) as the reference method. MALDI-TOF MS was able to correctly identify 112 NAS isolates from bovine IMI at species level out of a total of 115 (97.4%). These results were considered definitive and thus compared with those from the PCR-RFLP analyses. Only 50% (56/112) of the samples classified through groEL PCR-RFLP matched the molecular identity determined by MALDI-TOF MS, whereas coincidence rose to 96.4% (108/112) when comparing results from gap PCR-RFLP and the spectral analysis. This study demonstrates that gap PCR-RFLP is a useful and reliable tool for the identification of NAS species isolated from bovine mastitis.

Effects of Dietary Vibroactivated Clinoptilolite Supplementation on the Intramammary Microbiological Findings in Dairy Cows

Simple Summary

This study aimed to determine the effects of dietary vibroactivated clinoptilolite supplementation on the intramammary microbiological findings in dairy cows, causative agents of intramammary infection, and their sensitivity to antibiotics. The cows (n = 78) were randomly divided into two groups: the clinoptilolite (CPL)-treated group that received 100 g of clinoptilolite (CPL) in-feed (n = 38) from the seventh month of pregnancy to 75 days after calving and the control group (CON) of untreated cows (n = 40). Milk samples were taken from each cow on days 7, 25, 45, and 75 postpartum. Different causative pathogens were isolated in 86 udder quarters (7.07%), in 3.87% environmental microflora, and 89.06% were bacteriologically negative. The most effective antibiotics were cefoperazone and amoxicillin-clavulanic acid, while cloxacillin and tetracycline were the least effective. In the CPL group (14 cows), nine pathogens were isolated in 27 quarters, while in the control (CON) group (24 cows), 13 pathogens in 59 quarters. Cows from the CON group had a 1.96 times higher risk of intramammary infection than cows from the CPL group.

Abstract

The aim of this study was to determine the effects of dietary vibroactivated clinoptilolite supplementation on the intramammary microbiological findings in dairy cows, causative agents of potential intramammary infection, and their sensitivity to antibiotics. Cows (n = 78) were randomly divided into two groups: CPL-treated group that received clinoptilolite (CPL) in-feed (n = 38), i.e., 50 g natural powdered zeolite CPL, twice daily from the seventh month of pregnancy to 75 days after calving, and the control group (CON) of untreated cows (n = 40). Milk samples were taken from each cow on days 7, 25, 45, and 75 postpartum. The following causative pathogens were isolated in 86 udder quarters: Staphylococcus aureus in 5.81% of positive samples, Staphylococcus spp. 9.32%, coagulase-negative Staphylococcus (CNS) 22.09%, Streptococcus uberis 13.95%, Streptococcus agalactiae 1.16%, Streptococcus sp. 3.49%, Escherichia coli 8.13%, Enterococcus spp. 6.98%, Corynebacterium spp. 11.63%, Pasteurella sp. 10.47%, Serratia spp. 2.33%, and Arcanobacterium pyogenes, Citrobacter sp., Prototheca sp., and yeasts each in 1.16% of samples. Additionally, 3.87% of environmental microflora samples (n = 47) and 89.06% of udder samples (n = 1083) were bacteriologically negative. The most effective antibiotics were cefoperazone and amoxicillin-clavulanic acid, while cloxacillin and tetracycline were the least effective antibiotics in both groups. In the clinoptilolite supplemented (CPL) group (n = 38) of 14 cows, nine causative agents of mastitis were isolated in 27 quarters, while in the control (CON) group (n = 40) of 24 cows, 13 causative agents of mastitis were isolated in 59 quarters. Cows from the CON group had a 1.96 times higher risk of intramammary infection than cows from the CPL group during the observation period (odds ratio = 1.96, p = 0.0031; 95% CI = 1.2570–3.0770).

Non-S. aureus staphylococci (NAS) in milk samples: Infection or contamination?

Non-S. aureus staphylococci (NAS) are the most frequently isolated pathogens from bovine milk and can cause intramammary infections (IMI). They can also be found in teat canals, on bovine skin and in cows' environment, which may lead to unnoticed contamination of milk samples. The aim of this study was to investigate the role of NAS species as mastitis-causing pathogens or contaminants, and to identify possible differences between NAS species. A longitudinal study was conducted with consecutive milk sampling in five German dairy herds. Species identification was performed using matrix-assisted laser desorption ionization-time of flight mass spectrometry. Infections were distinguished from contaminations using two different definitions based on the repeated detection of an NAS species. Of 15 NAS species found, eight and ten, respectively, were associated with an IMI. Staphylococcus simulans and S. chromogenes were associated with IMI in more than 90 % of the findings. S. warneri, S. xylosus, S. microti, S. haemolyticus, and S. succinus seem to be frequent causes of IMI as well as contaminants. If a species-differentiation is available after cultivating NAS, the findings should be interpreted in consideration of the observations made in this study, whether it is more likely a question of a contaminant or a cause of intramammary infection. The bacteria shedding intensity of the NAS species with a more substantially adverse effect on udder health seems to be higher than that of the less important NAS pathogens.

Characterization and molecular epidemiology of Staphylococcus aureus strains resistant to beta-lactams isolated from the milk of cows diagnosed with subclinical mastitis

BACKGROUND AND AIM

The term ESKAPE, recognized by the WHO, is an acronym, which refers to the pathogens Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp., which is extremely virulent and multidrug-resistant. Although the term is used to designate nosocomial pathogens, in a milking environment, strains of Methicillin-resistant S. aureus have been isolated from cattle diagnosed with clinical and subclinical mastitis. Resistant strains may be involved in the transfer of genes conferring resistance to beta-lactam antimicrobials among the species of microorganisms related to mastitis etiology. This study aimed to trace the phenotypic and genotypic profiles of susceptibility to beta-lactams in S. aureus isolated from milk of cattle diagnosed with subclinical mastitis obtained from different rural properties located in the North of Minas Gerais State, Brazil.

MATERIALS AND METHODS

Sixteen microorganisms previously identified as S. aureus isolated from milk of cattle diagnosed with subclinical mastitis were submitted to matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF), mass spectrometry, and polymerase chain reaction (PCR) analysis for microbial species confirmation. The S. aureus beta-lactams antimicrobial phenotypic resistance profile was investigated by disk diffusion method. PCR methods were also performed to investigate the S. aureus genotypic beta-lactams resistance profile. For this purpose, bla Z, mec A, mec ALGA251, bla Oxa23, and bla KPC genes were screened among S. aureus isolates. The genetic diversity of S. aureus by fingerprint random amplified polymorphic DNA (RAPD)-PCR was also performed in this study.

RESULTS

All isolates showed phenotypic resistance to at least three beta-lactams, among which was meropenem. None of the isolates tested positive for the genes mec ALGA251, bla Oxa23, and bla KPC; however, the presence of the genes bla Z and mecA was detected among the isolates. The fingerprint analysis divided isolates into two distinct groups and 15 different subgroups. Despite the presence of clonality among the isolates, the PCR-RAPD analysis unveiled a heterogeneous profile with genetic diversity among the S. aureus isolates.

CONCLUSION

In this study, we identified beta-lactams resistant S. aureus strains isolated from the milk of cows diagnosed with subclinical mastitis. The S. aureus beta-lactams resistance was investigated using a phenotypic and genotypic approach. We believe that molecular epidemiology, improved knowledge, and genetic basis of resistance to beta-lactams might assist in asserting guidelines for better management practices of dealing with subclinical mastitis and mapping of origin of resistant pathogens in the studied Brazilian area.