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

Coagulase-negative staphylococci from bovine milk: Antibiogram profiles and virulent gene detection

BACKGROUND

Coagulase-negative Staphylococcus species are an emerging cause of intramammary infection, posing a significant economic and public health threat. The aim of this study was to assess the occurrence of coagulase-negative Staphylococcus species in bovine milk and dairy farms in Northwestern Ethiopia and to provide information about their antibiotic susceptibility and virulence gene profiles.

METHODS

The cross-sectional study was conducted from February to August 2022. Coagulase-negative Staphylococcus species were isolated from 290 milk samples. Species isolation and identification were performed by plate culturing and biochemical tests and the antimicrobial susceptibility pattern of each isolate was determined by the Kirby-Bauer disc diffusion test. The single-plex PCR was used to detect the presence of virulent genes. The STATA software version 16 was used for data analysis. The prevalence, proportion of antimicrobial resistance and the number of virulent genes detected from coagulase-negative Staphylococcus species were analyzed using descriptive statistics.

RESULTS

Coagulase-negative Staphylococcus species were isolated in 28.6%, (95% CI: 23.5-34.2) of the samples. Of these, the S. epidermidis, S. sciuri, S. warneri, S. haemolyticus, S. simulans, S. chromogens, S. cohnii, and S. captis species were isolated at the rates of 11, 5.2, 3.4, 3.1, 3.1, 1, 1, and 0.7% respectively. All the isolates showed a high percentage (100%) of resistance to Amoxicillin, Ampicillin, and Cefotetan and 37.5% of resistance to Oxacillin. The majority (54.2%) of coagulase-negative isolates also showed multidrug resistance. Coagulase-negative Staphylococcus species carried the icaD, pvl, mecA, hlb, sec, and hla virulent genes at the rates of 26.5%, 22.1%, 21.7%, 9.6%, 9.6% and 8.4% respectively.

CONCLUSION

The present study revealed that the majority of the isolates (54.2%) were found multidrug-resistant and carriage of one or more virulent and enterotoxin genes responsible for intramammary and food poisoning infections. Thus, urgent disease control and prevention measures are warranted to reduce the deleterious impact of coagulase-negative species. To the best of our knowledge, this is the first study in Ethiopia to detect coagulase-negative Staphylococcus species with their associated virulent and food poisoning genes from bovine milk.

An update on non-aureus staphylococci and mammaliicocci in cow milk: unveiling the presence of Staphylococcus borealis and Staphylococcus rostri by MALDI-TOF MS

Non-aureus staphylococci and mammaliicocci (NASM) are the microorganisms most frequently isolated from milk. Given their numerosity and complexity, MALDI-TOF MS is one of the preferred species identification approaches. Nevertheless, reference mass spectra for the novel species Staphylococcus borealis were included only recently in the Bruker Biotyper System (MBT) library, and other species of veterinary interest such as S. rostri are still absent. This work provides an updated picture of the NASM species found in milk, gained by retrospectively analyzing the data relating to 21,864 milk samples, of which 6,278 from clinical mastitis (CM), 4,039 from subclinical mastitis (SCM), and 11,547 from herd survey (HS), with a spectrum library including both species. As a result, S. borealis was the second most frequently isolated NASM (17.07%) after S. chromogenes (39.38%) in all sample types, with a slightly higher percentage in CM (21.84%), followed by SCM (17.65%), and HS (14.38%). S. rostri was also present in all sample types (3.34%), reaching 8.43% of all NASM in SCM and showing a significant association (p < 0.01) with this condition. Based on our findings, the presence of S. borealis and S. rostri in milk and their potential association with mastitis might have been overlooked, possibly due to the difficulties in differentiating these species from other closely related NASM. Our results indicate that S. borealis could be a more frequent contributor to bovine udder infections than previously thought and that S. rostri should also not be underestimated considering its significant association with SCM.

Divergent Immune Responses to Minor Bovine Mastitis-Causing Pathogens

Traditionally, non-aureus staphylococci and mammaliicocci (NASM) were not considered significant players in bovine mastitis. This study investigated the involvement of NASM (Staphylococcus hominis and Staphylococcus chromogenes) and lactic acid bacteria (LAB) strains (Weissella paramesenteroides) through bovine neutrophil responses. Bovine neutrophils displayed minimal apoptosis upon NASM and LAB challenge. Neutrophils expressed high TLR2 after challenge, but TLR6 expression varied and remained low in NASM pathogen recognition. Bovine neutrophils effectively engulfed and killed LAB, but their activity was significantly impaired against NASM. This was evident in S. chromogenes, where reduced TLR6 recognition and a weakened phagocytic response likely contributed to a lower bactericidal effect. Regardless of the bacteria encountered, intracellular ROS production remained high. S. chromogenes-challenged neutrophils displayed upregulation in genes for pathogen recognition (TLRs), ROS production, and both pro- and anti-apoptotic pathways. This response mirrored that of Weissella. except for CASP9 and BCL2, suggesting these bacteria have divergent roles in triggering cell death. Our findings suggest that S. chromogenes manipulates bovine neutrophil defenses through coordinated changes in functional responses and gene expression, while LAB strains have a weaker influence on apoptosis.

Frequency of non-aureus staphylococci and mammaliicocci species isolated from quarter clinical mastitis: A 6-year retrospective study

Non-aureus staphylococci and mammaliicocci (NASM) are the most frequently isolated bacterial group from bovine milk samples. Most studies focus on subclinical mastitis caused by NASM; however, NASM can cause clinical mastitis (CM) as well. We evaluated retrospective data from 6 years (2017-2022) to determine the species and frequency of NASM isolated from quarter bovine CM. The data was comprised of microbiological results from quarter CM samples routinely submitted to Quality Milk Production Services at Cornell University for microbial identification by MALDI-TOF mass spectrometry. A total of 9,909 microbiological results from 410 dairy herds were evaluated. Our results showed that 29 distinct NASM species were identified, with the 8 most prevalent NASM species being Staphylococcus chromogenes, Staphylococcus haemolyticus, Staphylococcus simulans, Staphylococcus epidermidis, Staphylococcus sciuri (now Mammaliicoccus sciuri), Staphylococcus agnetis/Staphylococcus hyicus, Staphylococcus borealis, and Staphylococcus xylosus. The NASM distribution remained similar among seasons, but the frequency of NASM CM cases was higher during the summer. Our results showed different patterns of variations in the isolation frequency over time, depending on the bacterial species: increasing or decreasing trends, cyclic fluctuations, and, except for Staphylococcus borealis, a significant seasonality effect for our study's most prevalent NASM. This study showed that Staphylococcus chromogenes remains the most frequent (43%) NASM species identified from bovine CM, followed by Staphylococcus haemolyticus (18%), and Staphylococcus simulans (12%).

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.

Associations between early lactation intramammary infections and udder health and performance during the first 180 days in milk in first-lactation organic dairy cows

Prior data from our group showed that first-lactation cows under organic management in United States have a high prevalence of Staphylococcus aureus, Streptococcus spp., and Staphylococcus chromogenes intramammary infections (IMI) in early lactation. Nonetheless, the relationship between IMI, udder health, and milk production in organically reared primiparous cows remains elusive. The objectives of this observational study were to investigate the relationship between presence and persistence of IMI in the first 35 d in milk (DIM) and somatic cell count (SCC) and milk production during the first 6 mo of lactation on first-lactation organic dairy cows. The analysis included a total of 1,348 composite milk samples collected during the first 35 DIM that were submitted for milk culture and 1,674 Dairy Herd Improvement Association (DHIA) tests during the first 180 DIM from 333 heifers in 4 organic dairy farms, enrolled between February 2019 and January 2020. The association between IMI in the first 35 DIM and new high SCC (SCC > 200,000 cells/mL) and milk production during the first 6 mo of lactation was investigated using Cox proportional hazards regression and mixed linear regression, respectively. The association between IMI persistence (harboring the same microorganism as reported by the laboratory for 2 or more samples) in the first 35 DIM and number of DHIA tests with high SCC during the first 6 mo of lactation was modeled using negative binomial regression. The presence of IMI by Staph. aureus (hazard ratio [HR] [95% confidence interval {CI}]: 3.35 [2.64, 4.25]) or Streptococcus spp. (HR [95% CI]: 2.25 [2.12, 2.39]) during the first 35 DIM was associated with an increased risk of new high SCC during the first 6 mo of lactation. Milk production was reduced when Streptococcus spp. were identified in milk samples. However, there was no evidence of a difference in milk production in Staph. aureus IMI. Isolation of non-aureus staphylococci and mammaliicocci was related to a mild increase in the hazards of high SCC (HR [95% CI]: 1.34 [0.97, 1.85]) and a decrease in milk production during one or more postpartum tests. Presence of gram-negative or Streptococcus-like organisms IMI was not associated with either high SCC or milk production. Presence of Bacillus IMI was associated with a lower hazard of new high SCC (HR [95% CI]: 0.45 [0.30, 0.68]), and higher milk production during the first 180 d of lactation (overall estimate [95% CI]: 1.7 kg/d [0.3, 3.0]). The persistence of IMI in the first 35 DIM was associated with the number of tests with high SCC during the lactation for all microorganisms except for Staphylococcus chromogenes. Therefore, our results suggest that the persistence of IMI in the first 35 DIM could be an important factor to understand the association between IMI detected in early lactation and lactational SCC and milk production in organic dairy heifers. Our study described associations between IMI, udder health, and milk production in first-lactation organic dairy cows that are consistent with findings from conventional dairy farms.

Genomic features and pathophysiological impact of a multidrug-resistant Staphylococcus warneri variant in murine mastitis

Non-aureus staphylococci (NAS) represent a major etiological agent in dairy animal mastitis, yet their role and impact remain insufficiently studied. This study aimed to elucidate the genomic characteristics of a newly identified multidrug-resistant NAS strain, specifically Staphylococcus warneri G1M1F, isolated from murine feces in an experimental mastitis model. Surprisingly, NAS species accounted for 54.35 % of murine mastitis cases, with S. warneri being the most prevalent at 40.0 %. S. warneri G1M1F exhibited resistance to 10 major antibiotics. Whole-genome sequencing established a genetic connection between G1M1F and S. warneri strains isolated previously from various sources including mastitis milk in dairy animals, human feces and blood across diverse geographical regions. Genomic analysis of S. warneri G1M1F unveiled 34 antimicrobial resistance genes (ARGs), 30 virulence factor genes (VFGs), and 278 metabolic features. A significant portion of identified ARGs (64 %) conferred resistance through antibiotic efflux pumps, while VFGs primarily related to bacterial adherence and biofilm formation. Inoculation with G1M1F in mice resulted in pronounced inflammatory lesions in mammary and colon tissues, indicating pathogenic potential. Our findings highlight distinctive genomic traits in S. warneri G1M1F, signifying the emergence of a novel multidrug-resistant NAS variant. These insights contribute to understanding NAS-related mastitis pathophysiology and inform strategies for effective treatment in dairy animals.

Efficacy of novel staphylococcal surface associated protein vaccines against Staphylococcus aureus and non-aureus staphylococcal mastitis in dairy cows

Mastitis is an inflammation of the mammary gland commonly caused by bacteria or fungi. Staphylococcus aureus is a major bacterium that causes mastitis in dairy cows. Non-aureus staphylococci are also increasingly reported, with Staphylococcus chromogenes being the most common species. Current staphylococcal mastitis control programs are not fully effective, and treatment with antibiotics is not sustainable. Non-antibiotic sustainable control tools, such as effective vaccines, are critically needed. We previously developed S. aureus surface-associated proteins (SASP) and S. chromogenes surface-associated proteins (SCSP) vaccines that conferred partial protective effects. We hypothesized that vaccination with SASP or SCSP would reduce the incidence of S. aureus mastitis throughout the lactation period. The objective of this study was to evaluate the efficacy of SASP and SCSP vaccines against S. aureus and non-aureus staphylococcal mastitis under natural exposure over 300 days of lactation. Pregnant Holstein dairy cows (n = 45) were enrolled and assigned to receive SASP (n = 15) or SCSP (n = 16) vaccines or unvaccinated control (n = 14). Cows were vaccinated with 1.2 mg of SASP or SCSP with Emulsigen-D adjuvant. Control cows were injected with phosphate-buffered saline with Emulsigen-D adjuvant. Three vaccine injections were given subcutaneously at 60, 40, and 20 days before the expected calving. Booster vaccinations were given at 120 and 240 days in milk. Cows were monitored for mastitis at quarter and cow levels, staphylococcal mastitis incidence, changes in serum and milk anti-SASP and anti-SCSP antibody titers, bacterial counts in milk, adverse reactions, milk yield and milk somatic cells count over 300 days of lactation. The SCSP vaccine conferred a significant reduction in the incidence of staphylococcal mastitis. Milk and serum anti-SASP and anti-SCSP antibody titers were increased in the vaccinated cows compared to unvaccinated control cows. Anti-SASP and anti-SCSP antibody titers decreased at about 120 days in milk, indicating the duration of immunity of about four months. In conclusion, the SASP and SCSP vaccines conferred partial protection from natural infection.

Non-aureus staphylococci and mammaliicocci isolated from bovine milk in Italian dairy farms: a retrospective investigation

Non-aureus staphylococci and mammaliicocci (NASM) are associated with bovine mastitis and increased milk somatic cell count (SCC) but their relationships with mammary gland health at the species level are not clearly defined. Regional differences have also been reported in their specific prevalence. The implementation of MALDI-TOF MS in milk microbiology is generating large and dependable datasets with the potential of providing useful epidemiological information. We present the retrospective analysis of 17,213 milk samples sent to our laboratory in 2021-2022, including 13,146 quarter samples from cows with subclinical (SCM) or clinical mastitis (CM) from 104 farms, and 4,067 composite herd survey (HS) samples from 21 farms. NASM were isolated from 21.12% of SCM, 11.49% of CM, and 15.59% of HS milk samples. The three most frequently identified NASM in SCM milk were Staphylococcus chromogenes (33.33%), S. haemolyticus (26.07%), and S. epidermidis (10.65%); together with S. microti and S. hyicus, these species were significantly more prevalent in quarters with SCM (p < 0.05). The three most frequently identified NASM in CM milk were S. chromogenes (31.69%), S. haemolyticus (21.42%), and Mammaliicoccus sciuri (18.38%), although no significant associations were found between these NASM species and CM. The three most frequently identified NASM in HS milk were S. chromogenes (44.49%), S. epidermidis (17.84%), and S. haemolyticus (17.23%), with S. chromogenes being isolated in all the farms sending HS milk (100%). In conclusion, this retrospective study provides the first information on the NASM species isolated from cow milk in Italy, expanding our knowledge on the epidemiology of NASM at the species level and providing further insights into their relationships with mammary gland health in modern dairy farms.

Non-aureus staphylococci and mammaliicocci (NASM): their role in bovine mastitis and One Health

Non-aureus staphylococci (NAS) are gaining importance in mastitis and public health, and some NAS have been reclassified as mammaliicocci (NASM). Bovine milk production has a major influence on the world economy, being an essential source of income for small, medium and large producers, and bovine mastitis caused by NASM can cause an economic impact. Mastitis generates financial losses due to reduced revenue, increased veterinary costs and expenses associated with animal slaughter. However, it is also a public health issue involving animal health and welfare, human health and the ecosystem. Furthermore, it is an increasingly common infection caused by NASM, including antimicrobial-resistant strains. Despite all these adverse effects that NASM can cause, some studies also point to its protective role against mastitis. Therefore, this review article addresses the negative and positive aspects that NASM can cause in bovine mastitis, the virulence of the disease and resistance factors that make it difficult to treat and, through the One Health approach, presents a holistic view of how mastitis caused by NASM can affect both animal and human health at one and the same time.

Host DNA depletion methods and genome-centric metagenomics of bovine hindmilk microbiome

Bovine mastitis is a multi-etiological and complex disease, resulting in serious economic consequences for dairy farmers and industry. In recent years, the microbiological evaluation of raw milk has been investigated in-depth using next-generation sequencing approaches such as metataxonomic analysis. Despite this, host DNA is a major concern in the shotgun metagenomic sequencing of microbial communities in milk samples, and it represents a big challenge. In this study, we aimed to evaluate different methods for host DNA depletion and/or microbial DNA enrichment and assess the use of PCR-based whole genome amplification in milk samples with high somatic cell count (SCC) by using short- and long-read sequencing technologies. Our results evidenced that DNA extraction performed differently in terms of host DNA removal, impacting metagenome composition and functional profiles.. Moreover, the ratio of SCC/bacteria ultimately impacts microbial DNA yield, and samples with low SCC (SCC below 100,000 cells/mL) are the most problematic. When milk samples with high SCC (SCC above 200,000 cells/mL) underwent multiple-displacement amplification (MDA), we successfully recovered high-quality metagenome-assembled genomes (MAGs), and long-read sequencing was feasible even for samples with low DNA concentration. By associating MDA and short-read sequencing, we recovered two times more MAGs than in untreated samples, and an ongoing co-infection not reported by traditional methods was detected for mastitis pathogen. Overall, this new approach will improve the detection of mastitis-associated microorganisms and make it possible to examine host-microbiome interactions in bovine mastitis.IMPORTANCENext-generation sequencing technologies have been widely used to gain new insights into the diversity of the microbial community of milk samples and dairy products for different purposes such as microbial safety, profiling of starter cultures, and host-microbiome interactions. Milk is a complex food matrix, and additionally, the presence of host nucleic acid sequences is considered a contaminant in untargeted high-throughput sequencing studies. Therefore, genomic-centric metagenomic studies of milk samples focusing on the health-disease status in dairy cattle are still scarce, which makes it difficult to evaluate the microbial ecophysiology of bovine hindmilk. This study provides an alternative method for genome-centric metagenome studies applied to hindmilk samples with high somatic cell content, which is indispensable to examining host-microbiome interactions in bovine mastitis.

Investigation of intramammary infections in primiparous cows during early lactation on organic dairy farms

Previous studies have shown that organically raised dairy cows have an increased prevalence of Staphylococcus aureus compared with conventionally raised dairy cows. However, little information exists about the dynamics of intramammary infection (IMI) in primiparous cows during early lactation on organic dairy farms. The objective of this study was to describe the IMI dynamics of primiparous cows on certified organic farms during early lactation. This longitudinal study enrolled 503 primiparous cows from 5 organic dairy farms from February 2019 to January 2020. Quarter-level milk samples were collected aseptically on a weekly basis during the first 5 wk of lactation. Samples were pooled by cow and time point into composite samples inside a sterilized laminar hood and submitted for microbiological culture. For each of the different microorganisms identified, we estimated the prevalence in each postpartum sample, period prevalence (PP), cumulative incidence, and persistence of IMI. Logistic regression models were used to investigate whether the prevalence of IMI differed by farm or sampling time points and whether IMI persistence differed between detected microorganisms. Our findings revealed a high prevalence of Staphylococcus aureus (PP = 18.9%), non-aureus staphylococci and closely related mammaliicoccal species (PP = 52.1%), and Streptococcus spp. and Streptococcus-like organisms (PP = 32.1%) within the study population. The prevalence of these microorganisms varied significantly between farms. Staphylococcus aureus and Staphylococcus chromogenes exhibited significantly higher IMI persistence compared with other detected bacterial taxa, confirming the divergent epidemiological behavior in terms of IMI chronicity across different microorganisms. This study improves our understanding of the epidemiology of mastitis-causing pathogens in organically raised primiparous cows, which can be used to tailor mastitis control plans for this unique yet growing subpopulation of dairy cows.

Intramammary infections and risk factors in freshly calved heifers in Swedish dairy herds

Subclinical mastitis can be common among freshly calved heifers (FCH), but the prevalence differs between herds, possibly due to variation in risk factors. The aims of this observational study were to identify differences in occurrence of intramammary infection (IMI) in FCH between herds with documented good or poorer first-parity udder health based on cow somatic cell count (CSCC) in early lactation, and to study herd differences in animal factors important for udder health, such as udder and hock skin lesions and animal cleanliness. Three groups of herds were included: those with high proportions of FCH with low CSCC (≤75,000 cells/mL) at the first 2 milk recordings after calving (LL), herds with high proportions of FCH with high CSCC (>100,000 cells/mL) at the first and low CSCC at the second recording (HL), and herds with high proportions of FCH with high CSCC at both recordings (HH). Thirty-nine herds (13 LL, 11 HL, 15 HH) were visited 3 times during a 12-mo period for observation of cleanliness and hock lesions, and sampling of udder and teat skin using swab cloths of milk-fed calves, early-pregnant heifers, and late-pregnant heifers. In 25 (9 LL, 9 HL, 7 HH) udder quarter samples from colostrum and milk on d 3 to 4 after calving were taken by the farmers from FCH during one year. The farmers also provided information on calving (individual or group), use of restraint and oxytocin at milking, and presence of teat and udder skin lesions. Bacterial growth in swab samples and quarter samples was investigated by culturing, and a selection of isolates was genotyped using whole-genome sequencing. Cleanliness, hock and udder skin lesions other than udder-thigh dermatitis, and growth of bacteria in swab samples did not differ between herd groups. It was more common that FCH from LL herds, compared with FCH in HH and HL herds, calved in a group of animals. Use of restraint at milking was more common in LL herds than in HH herds, whereas presence of udder-thigh dermatitis was lowest in LL herds. Specific infection was found in 14% of 5,593 quarter samples from 722 FCH. The most common IMI was Staphylococcus chromogenes. Growth of Staphylococcus simulans was more common in HH than in LL and HL herds. In colostrum samples, Staphylococcus haemolyticus was more common in HL and HH than in LL herds. The proportion of quarters with the same specific infection at both samplings was higher in HH than in LL herds and tended to be higher in HH than in HL herds. The proportion of quarters with Staph. chromogenes IMI at both samplings tended to differ between herd groups and was highest in HH herds. Whole-genome sequencing found the same sequence type of Staph. chromogenes and Staphylococcus aureus in both samples in almost all quarters with the same infection at both samplings. The differences in IMI between herd groups were in line with the higher somatic cell count in HH herds. The reasons for the predominance of Staph. chromogenes IMI in FCH need further studies.

Genotypic characterization of Staphylococcus chromogenes and Staphylococcus simulans from Swedish cases of bovine subclinical mastitis

Staphylococcus chromogenes and Staphylococcus simulans are commonly found in intramammary infections (IMI) associated with bovine subclinical mastitis, but little is known about genotypic variation and relatedness within species. This includes knowledge about genes encoding antimicrobial resistance (AMR) and potential virulence factors (pVF). The aim of this study was therefore to investigate these aspects by whole-genome sequencing of milk isolates from Swedish dairy cows with subclinical mastitis in an observational study. We also wanted to study if specific genotypes were associated with persistent IMI and the inflammatory response at udder quarter level. In total, 105 and 118 isolates of S. chromogenes and S. simulans, respectively, were included. Isolates were characterized using a 7-locus multilocus sequence typing (7-MLST), core genome analysis and in-silico analysis of AMR and pVF genes. Forty-seven sequence types (ST) and 7 core genome clusters of S. chromogenes were identified, and the most common ST were ST-6 and ST-109, both belonging to cluster VII. A 7-locus MLST scheme for S. simulans was not available, but 3 core genome clusters and 5 subclusters were described. Overall, substantial variation in ST and clusters among cows and herds were found in both species. Some ST of S. chromogenes were found in several herds, indicating spread between herds. Moreover, within-herd spread of the same genotype was observed for both species. Only a few AMR genes [blaZ, strpS194, vga(A)] were detected in a limited number of isolates, with the exception of blaZ coding for β-lactamase, which was identified in 22% of the isolates of S. chromogenes with ST-19, ST-102, and ST-103 more commonly carrying this gene compared with other ST. However, the blaZ gene was not identified in S. simulans. The average total number of pVF detected per isolate was similar in S. chromogenes (n = 30) and S. simulans (n = 33), but some variation in total numbers and presence of specific pVF or functional groups of pVF, was shown between ST/clusters within species. Differences in inflammatory response and potentially in persistent IMI at udder quarter level were found between S. chromogenes subtypes but not between S. simulans subtypes. In conclusion, the results from the present study generates new insight into the epidemiology of bovine S. chromogenes and S. simulans IMI, which can have implications for future prevention and antimicrobial treatment of infections related to these species.

Comparison of non-aureus staphylococcal and mammaliicoccal species found in both composite milk and bulk-tank milk samples of dairy cows collected in tandem

Non-aureus staphylococci and the closely related mammaliicoccal species (NASM) are the most common causes of bovine subclinical mastitis on modern dairy farms and are highly prevalent in bulk-tank milk. The purpose of this study was to determine the distribution of NASM in both composite cow milk (CCM) and bulk-tank milk (BTM) samples collected in tandem in commercial Flemish dairy herds and to estimate the origin of the different (subgroups of) NASM species present in BTM by applying strain typing (random amplification of polymorphic DNA or random amplified DNA [RAPD]). A single cross-sectional sampling was performed over 5 herds that volunteered to participate in the study. Composite cow milk samples (n = 356) were collected from all lactating cows (except those with clinical mastitis) during a milking in tandem with 6 BTM samples per herd sequentially collected immediately post that milking (n = 30). In total, 421 and 80 NASM isolates were recovered and identified by MALDI-TOF mass spectrometry from the CCM and BTM samples, respectively and a total of 21 and 12 different NASM species were identified from CCM and BTM samples, respectively. Staphylococcus cohnii was the most prevalent NASM species found in BTM followed by Staphylococcus haemolyticus, Staphylococcus epidermidis, Mammaliicoccus lentus, and Staphylococcus equorum, whereas from CCM samples the most common species were S. hemolyticus, S. cohnii, S. equorum, S. epidermidis, and Staphylococcus chromogenes. The prevalent NASM species in both CCM and BTM samples was distinct for each herd, corroborating other studies observing a herd-specific NASM microbiota. Random amplified DNA analysis was performed on 9 NASM species (S. chromogenes, S. epidermidis, S. haemolyticus, S. equorum, Mammaliicoccus sciuri, Staphylococcus xylosus, S. cohnii, Staphylococcus debuckii, and M. lentus) because these species were isolated from both sample types in a herd. The same RAPD types were found in both sample types for all NASM species selected for strain typing in varying degrees. When assessing the distribution of NASM species, differences within NASM species should be examined meaning a closer look should be taken at the strain level rather than at the species level only.

Genomic analysis and assessment of pathogenic (toxicogenic) potential of Staphylococcus haemolyticus and Bacillus paranthracis consortia isolated from bovine mastitis in Russia

Three stable microbial consortia, each composed of Bacillus paranthracis and Staphylococcus haemolyticus strains, were isolated from milk of cows diagnosed with mastitis in three geographically remote regions of Russia. The composition of these consortia remained stable following multiple passages on culture media. Apparently, this stability is due to the structure of the microbial biofilms formed by the communities. The virulence of the consortia depended on the B. paranthracis strains. It seems plausible that the ability of the consortia to cause mastitis in cattle was affected by mutations of the cytK gene of B. paranthracis.

Exploring the distinct immunological reactions of bovine neutrophils towards major and minor pathogens responsible for mastitis

Bovine mastitis is primarily caused by a group of bacteria known as Staphylococcus and Streptococcus. However, additional types of bacteria, such as bovine non-aureus staphylococci and mammaliicocci (NASM) as well as lactic acid bacteria (LAB), are considered minor pathogens and have less impact on cows. Modulating bovine neutrophil activities and gene expressions in response to bacterial stimuli prompted the cells to execute effector functions to combat udder infections. Although neutrophils can manage major mastitis-causing bacteria, this strategy has not been tested against minor pathogens, i.e. NASM, Weissella spp. Our main objective was to investigate how neutrophils interacted with major and minor pathogens during in vitro bacterial stimulation. The results reveal that neutrophils performed offensive duties regardless of the type of bacteria encountered. Neutrophils generated high levels of reactive oxygen species, efficiently phagocytosed both types of bacteria, and facilitated extracellular killing by releasing NET structures against all bacteria. In addition, neutrophils migrated preferentially towards the majors rather than the minors, although myeloperoxidase (MPO) degranulation did not differ substantially across bacteria. Furthermore, the killing capacity of neutrophils was not dependent on any particular bacterium. The correlation of effector functions is intimately linked to the up-regulation of genes associated with the above functions, except for IL6, which was down-regulated. Furthermore, neutrophil apoptosis can be modulated by altering apoptosis-associated genes in response to harmful stimuli. These findings provide valuable information on how neutrophils react to major and minor mastitis-causing bacteria. However, future research should explore the interplay between minor pathogens and the host's responses.

Genomic Insights into Methicillin-Resistant Staphylococci and Mammaliicocci from Bulk Tank Milk of Dairy Farms in Serbia

The potential risk to human and animal health provides a rationale for research on methicillin-resistant staphylococci (MRS) and mammaliicocci (MRM) in dairy herds. Here, we aimed to estimate their occurrence in the bulk tank milk (BTM) samples collected in 2019-2021 from 283 bovine dairy farms in the Belgrade district. We used whole-genome sequencing to characterize the obtained isolates and assess their genetic relatedness. A total of 70 MRS/MRM were recovered, most frequently Staphylococcus haemolyticus and Mammaliicoccus sciuri. Five clusters of 2-4 genetically related isolates were identified and epidemiological data indicated transmission through, e.g., farm visits by personnel or milk collection trucks. Most MRSA isolates belonged to the typical livestock-associated lineage ST398-t034. One MRSA isolate (ST152-t355) harbored the PVL-encoding genes. Since MRS/MRM isolates obtained in this study frequently harbored genes conferring multidrug resistance (MDR), this argues for their role as reservoirs for the spread of antimicrobial resistance genes. The pipeline milking system and total bacterial count >100,000 CFU/mL were significantly associated with higher occurrences of MRS/MRM. Our study confirms that BTM can be a zoonotic source of MRS, including MDR strains. This highlights the urgent need for good agricultural practices and the continuous monitoring of MRS/MRM in dairy farms.

Virulence Mechanisms of Staphylococcal Animal Pathogens

Staphylococci are major causes of infections in mammals. Mammals are colonized by diverse staphylococcal species, often with moderate to strong host specificity, and colonization is a common source of infection. Staphylococcal infections of animals not only are of major importance for animal well-being but have considerable economic consequences, such as in the case of staphylococcal mastitis, which costs billions of dollars annually. Furthermore, pet animals can be temporary carriers of strains infectious to humans. Moreover, antimicrobial resistance is a great concern in livestock infections, as there is considerable antibiotic overuse, and resistant strains can be transferred to humans. With the number of working antibiotics continuously becoming smaller due to the concomitant spread of resistant strains, alternative approaches, such as anti-virulence, are increasingly being investigated to treat staphylococcal infections. For this, understanding the virulence mechanisms of animal staphylococcal pathogens is crucial. While many virulence factors have similar functions in humans as animals, there are increasingly frequent reports of host-specific virulence factors and mechanisms. Furthermore, we are only beginning to understand virulence mechanisms in animal-specific staphylococcal pathogens. This review gives an overview of animal infections caused by staphylococci and our knowledge about the virulence mechanisms involved.

Genomic and Phenotypic Characterization of Mastitis-Causing Staphylococci and Probiotic Lactic Acid Bacteria Isolated from Raw Sheep's Milk

Dairy products play a crucial role in human nutrition as they provide essential nutrients. However, the presence of diverse microorganisms in these products can pose challenges to food safety and quality. Here, we provide a comprehensive molecular characterization of a diverse collection of lactic acid bacteria (LAB) and staphylococci isolated from raw sheep's milk. Whole-genome sequencing, phenotypic characterization, and bioinformatics were employed to gain insight into the genetic composition and functional attributes of these bacteria. Bioinformatics analysis revealed the presence of various genetic elements. Important toxin-related genes in staphylococci that contribute to their pathogenic potential were identified and confirmed using phenotypic assays, while adherence-related genes, which are essential for attachment to host tissues, surfaces in the dairy environment, and the creation of biofilms, were also present. Interestingly, the Staphylococcus aureus isolates belonged to sequence type 5, which largely consists of methicillin-susceptible isolates that have been involved in severe nosocomial infections. Although genes encoding methicillin resistance were not identified, multiple resistance genes (RGs) conferring resistance to aminoglycosides, macrolides, and fluroquinolones were found. In contrast, LAB had few inherently present RGs and no virulence genes, suggesting their likely safe status as food additives in dairy products. LAB were also richer in bacteriocins and carbohydrate-active enzymes, indicating their potential to suppress pathogens and effectively utilize carbohydrate substrates, respectively. Additionally, mobile genetic elements, present in both LAB and staphylococci, may facilitate the acquisition and dissemination of genetic traits, including RGs, virulence genes, and metabolic factors, with implications for food quality and public health. The molecular and phenotypic characterization presented herein contributes to the effort to mitigate risks and infections (e.g., mastitis) and enhance the safety and quality of milk and products thereof.

Molecular identification, antimicrobial resistance and virulence gene profiling of Staphylococcus spp. associated with bovine sub-clinical mastitis in Bangladesh

This study was conducted to investigate the diversity and antimicrobial resistance profiling of Staphylococcus species causing sub-clinical mastitis (SCM) in dairy herds in Bangladesh as well as putative risk factors associated with the infections. Individual quarter milk samples were collected from a total of 284 lactating cows from 30 dairy farms were screened by means of California mastitis test; 178 (62.7%) of them had at least of quarter affected by SCM. After conventional microbiological isolation procedures, PCR tests were used for Staphylococcus species identification and detection of antimicrobial resistance and virulence genes. S. chromogenes (65.7%) was the most predominant species followed by, S. epidermidis (20.2%), S. haemolyticus (19.1%), S. aureus (15.7%), and S. sciuri (5.6%). High levels of antimicrobial resistance to ampicillin and amoxicillin/clavulanic acid were observed in S. aureus (82.1% and 75%) and S. sciuri (80% and 70%), while resistance to cefepime was markedly higher in S. chromogenes (95.7%), S. haemolyticus (94.1%), and S. epidermidis (97.2%). Multidrug resistance isolates were identified in all five species. The mecA gene was detected in S. aureus (32.1%) and S. chromogenes (5.98%). In addition, 20% S. sciuri and 17.7% S. haemolyticus carried the cytotoxin (pvl) gene, while 14.3% S. aureus harbored the toxic shock syndrome toxin (tst) gene. Multivariable logistic regression analysis identified "Old aged" (OR [CI]: 3.5 [1-12.4]); "Early stage of lactation" (OR [CI]: 3.4 [1.2-9.7]) and, "Firm udder condition" (OR [CI]: 4.2 [1.2-14.6]) as risk factors associated with SCM caused by S. aureus, S. chromogenes, and S. haemolyticus, respectively. Moreover, "Use of antimicrobials" (OR [CI]: 10.4 [3.4-32.1] and "History of previous clinical mastitis" (OR [CI]: 4.9 [1.2-19.7] for the carriage of methicillin-resistant Staphylococcus spp.

Non-aureus staphylococci and mammaliicocci as a cause of mastitis in domestic ruminants: current knowledge, advances, biomedical applications, and future perspectives - a systematic review

Non-aureus staphylococci and mammaliicocci (NASM) are one of the most common causes of subclinical mastitis in dairy animals and the extent of damage by intramammary infections (IMI) caused by NASM is still under debate. The different effects of NASM on the mammary gland may be associated with differences between bacterial species. NASM are normal and abundant colonizers of humans and animals and become pathogenic only in certain situations. The veterinary interest in NASM has been intense for the last 25 years, due to the strongly increasing rate of opportunistic infections. Therefore, the objective of this review is to provide a general background of the NASM as a cause of mastitis and the most recent advances that exist to prevent and fight the biofilm formation of this group of bacteria, introduce new biomedical applications that could be used in dairy herds to reduce the risk of chronic and recurrent infections, potentially responsible for economic losses due to reduced milk production and quality. Effective treatment of biofilm infection requires a dual approach through a combination of antibiofilm and antimicrobial agents. Even though research on the development of biofilms is mainly focused on human medicine, this technology must be developed at the same time in veterinary medicine, especially in the dairy industry where IMI are extremely common.

Severity of Clinical Mastitis and Bacterial Shedding

The aim of this cross-sectional study was to investigate associated factors of the severity of clinical mastitis (CM). Milk samples of 249 cases of CM were microbiologically examined, of which 27.2% were mild, 38.5% moderate, and 34.3% severe mastitis. The samples were incubated aerobically and anaerobically to investigate the role of aerobic and anaerobic microorganisms. In addition, the pathogen shedding was quantitatively examined, and animal individual data, outside temperature and relative humidity, were collected to determine associated factors for the severity of CM. The pathogen isolated the most was Escherichia coli (35.2%), followed by Streptococcus spp. (16.4%). Non-aureus staphylococci (NaS) (15.4%) and other pathogens (e.g., Staphylococcus aureus, coryneforms) (15.4%) were the pathogens that were isolated the most for mild mastitis. Moderate mastitis was mostly caused by E. coli (38%). E. coli was also the most common pathogen in severe mastitis (50.6%), followed by Streptococcus spp. (16.4%), and Klebsiella spp. (10.3%). Obligate anaerobes (Clostridium spp.) were isolated in one case (0.4%) of moderate mastitis. The mortality rate (deceased or culled due to the mastitis in the following two weeks) was 34.5% for severe mastitis, 21.7% for moderate mastitis, and 4.4% for mild mastitis. The overall mortality rate of CM was 21.1%. The pathogen shedding (back logarithmized) was highest for severe mastitis (55,000 cfu/mL) and E. coli (91,200 cfu/mL). High pathogen shedding, low previous somatic cell count (SCC) before mastitis, high outside temperature, and high humidity were associated with severe courses of mastitis.

Comparative Genomics of Staphylococcus rostri, an Undescribed Bacterium Isolated from Dairy Mastitis

This study characterizes 81 S. rostri isolates from bovine mastitis (of which 80 were subclinical). The isolates were first identified as S. microti by MALDI-TOF MS, but later whole genome sequencing analysis allowed reclassification as S. rostri. The isolates were derived from 52 cows and nine dairy herds in Denmark. To describe the pathogenicity of S. rostri, we used whole genome sequencing to infer the distribution of genes associated with virulence, antibiotic resistance, and mobile genetic elements. Also, we performed a core-genome phylogeny analysis to study the genetic relatedness among the isolates. All 81 isolates expressed the same virulence profile comprising two putative virulence genes, clpP and clpC. Three isolates carried a resistance gene encoding streptomycin (str) or lincomycin (lnuA) resistance. The distribution of plasmids suggested the detected antibiotic resistance genes to be plasmid-mediated. Phages were abundant among the isolates, and the single isolate from clinical mastitis acquired a phage disparate from the rest, which potentially could be involved with virulence in S. rostri. The core genome phylogeny revealed a strong genetic intra-herd conservation, which indicates the source of introduction being herd-specific and might further imply the ability of S. rostri to adapt to the bovine niche and spread from cow-to-cow in a contagious manner. With this study, we aim to acquaint clinicians and professionals with the existence of S. rostri which might have been overlooked so far.

Elucidation of the Bovine Intramammary Bacteriome and Resistome from healthy cows of Swiss dairy farms in the Canton Tessin

Healthy, untreated cows of nine dairy herds from the Swiss Canton Tessin were analyzed three times within one year to identify the most abundant species of the intramammary bacteriome. Aseptically collected milk samples were cultured and bacteria identified using MALDI-TOF. Of 256 cows analyzed, 96% were bacteriologically positive and 80% of the 1,024 quarters were positive for at least one bacterial species. 84.5% of the quarters were healthy with somatic cell counts (SCC) < 200,000 cells/mL, whereas 15.5% of the quarters showed a subclinical mastitis (SCC ≥ 200,000 cells/mL). We could assign 1,288 isolates to 104 different bacterial species including 23 predominant species. Non-aureus staphylococci and mammaliicocci (NASM) were most prevalent (14 different species; 73.5% quarters). Staphylococcus xylosus and Mammaliicoccus sciuri accounted for 74.7% of all NASM isolates. To describe the intramammary resistome, 350 isolates of the predominant species were selected and subjected to short-read whole genome sequencing (WGS) and phenotypic antibiotic resistance profiling. While complete genomes of eight type strains were available, the remaining 15 were de novo assembled with long reads as a resource for the community. The 23 complete genomes served for reference-based assembly of the Illumina WGS data. Both chromosomes and mobile genetic elements were examined for antibiotic resistance genes (ARGs) using in-house and online software tools. ARGs were then correlated with phenotypic antibiotic resistance data from minimum inhibitory concentration (MIC). Phenotypic and genomic antimicrobial resistance was isolate-specific. Resistance to clindamycin and oxacillin was most frequently observed (65 and 30%) in Staphylococcus xylosus but could not be linked to chromosomal or plasmid-borne ARGs. However, in several cases, the observed antimicrobial resistance could be explained by the presence of mobile genetic elements like tetK carried on small plasmids. This represents a possible mechanism of transfer between non-pathogenic bacteria and pathogens of the mammary gland within and between herds. The-to our knowledge-most extensive bacteriome reported and the first attempt to link it with the resistome promise to profoundly affect veterinary bacteriology in the future and are highly relevant in a One Health context, in particular for mastitis, the treatment of which still heavily relies on antibiotics.

The Impact of Low-Level Benzalkonium Chloride Exposure on Staphylococcus spp. Strains and Control by Photoinactivation

Exposure of bacteria to low concentrations of biocides can facilitate horizontal gene transfer, which may lead to bacterial adaptive responses and resistance to antimicrobial agents. The emergence of antibacterial resistance not only poses a significant concern to the dairy industry but also adds to the complexity and cost of mastitis treatment. This study was aimed to evaluate how selective stress induced by benzalkonium chloride (BC) promotes antibiotic non-susceptibility in Staphylococcus spp. In addition, we investigated the efficacy of photodynamic inactivation (PDI) in both resistant and susceptible strains. The study determined the minimum inhibitory concentration (MIC) of BC using the broth microdilution method for different Staphylococcus strains. The experiments involved pairing strains carrying the qacA/qacC resistance genes with susceptible strains and exposing them to subinhibitory concentrations of BC for 72 h. The recovered isolates were tested for MIC BC and subjected to disc diffusion tests to assess changes in susceptibility patterns. The results demonstrated that subinhibitory concentrations of BC could select strains with reduced susceptibility and antibiotic resistance, particularly in the presence of S. pasteuri. The results of PDI mediated by toluidine blue (100 µM) followed by 60 min irradiation (total light dose of 2.5 J/cm2) were highly effective, showing complete inactivation for some bacterial strains and a reduction of up to 5 logs in others.

Prevalence of udder pathogens in milk samples from Norwegian dairy cows recorded in a national database in 2019 and 2020

BACKGROUND

Identification of aetiological agents of mastitis in dairy cattle is important for herd management of udder health. In Norway, results from mastitis diagnostics are systematically recorded in a central database, so that the dairy industry can follow trends in the recorded frequency of udder pathogens and antimicrobial resistance patterns at national level. However, bacteriological testing of milk samples is based on voluntary sampling, and data are therefore subject to some bias. The aim of this study was to examine the prevalence of udder pathogens in Norwegian dairy cows by analysing data from the national routine mastitis diagnostics and to explore how routines for sampling and diagnostic interpretations may affect the apparent prevalence of different bacterial pathogens. We also assessed associations between udder pathogen findings and the barn- and milking systems of the herds.

RESULTS

The most frequently detected major udder pathogens among all milk samples submitted for bacterial culture (n = 36,431) were Staphylococcus aureus (24.5%), Streptococcus dysgalactiae (13.3%) and Streptococcus uberis (9.0%). In the subset of samples from clinical mastitis (n = 7598); Escherichia coli (14.5%) was the second most frequently detected pathogen following S. aureus (27.1%). Staphylococcus epidermidis (10.0%), Corynebacterium bovis (9.4%), and Staphylococcus chromogenes (6.0%) dominated among the minor udder pathogens. Non-aureus staphylococci as a group, identified in 39% of the sampling events, was the most frequently identified udder pathogen in Norway. By using different definitions of cow-level bacterial diagnoses, the distribution of minor udder pathogens changed. Several udder pathogens were associated with the barn- and milking system but the associations were reduced in strength when data were analysed from farms with a comparable herd size. S. aureus was associated with tiestall housing, E. coli and S. dysgalactiae were associated with freestall housing, and S. epidermidis was associated with automatic milking systems. Only 2.5% of the 10,675 tested S. aureus isolates were resistant to benzylpenicillin. Among the 2153 tested non-aureus staphylococci, altogether 34% were resistant to benzylpenicillin.

CONCLUSIONS

This study presents the recorded prevalence of udder pathogens in Norway over a two-year period and assesses the possible impact of the sampling strategies, diagnostic methods and diagnostic criteria utilized in Norway, as well as associations with different housing and milking systems. The national database with records of results from routine mastitis diagnostics in Norway provides valuable information about the aetiology of bovine mastitis at population level and can reveal shifts in the distribution and occurrence of udder 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.

Staphylococcus aureus coa gene sequence analysis can prevent misidentification of coagulase-negative strains and contribute to their control in dairy cow herds

Accurate and precise differentiation of staphylococci isolated from milk is of importance for udder health management. In particular, the rapid and specific identification of Staphylococcus aureus plays an essential role in the prevention and treatment programs for bovine mastitis. Plasma gelatinization in coagulase assays is routinely used to discriminate S. aureus from other species by detecting the presence of extracellular free staphylocoagulase. However, rarely occurring coagulase-deficient S. aureus strains can be responsible for clinical and subclinical mastitis cases. By investigating S. aureus isolates from a single herd over a 10-year period we identified the persistence of a phenotypically coagulase-negative S. aureus strain and pinpointed the possible cause to a single base pair deletion in the coa gene sequence. Our results support the need to integrate primary biochemical tests with molecular/sequence analysis approaches for correctly identifying and discriminating atypical S. aureus in bovine herds, as the coagulase test alone may fail to detect persistent mastitis-causing strains.

Priming of the murine mammary gland with Staphylococcus chromogenes IM reduces bacterial growth of Streptococcus uberis: a proof-of-concept study

Streptococcus uberis is a major causative agent of bovine mastitis, an inflammation of the mammary gland with substantial economic consequences. To reduce antibiotic use in animal agriculture, alternative strategies to treat or prevent mastitis are being investigated. Bovine-associated non-aureus staphylococci are proposed in that respect due to their capacity to inhibit the in vitro growth of S. uberis. We demonstrate that priming the murine mammary gland with Staphylococcus chromogenes IM reduces S. uberis growth in comparison with non-primed glands. The innate immune system is activated by increasing IL-8 and LCN2, which may explain this decreased growth.

Bovine-associated staphylococci and mammaliicocci trigger T-lymphocyte proliferative response and cytokine production differently

We examined whether distinct staphylococcal and mammaliicoccal species and strains trigger B- and T-lymphocyte proliferation and interleukin (IL)-17A and interferon (IFN)-γ production by peripheral blood mononuclear cells in nulliparous, primiparous, and multiparous dairy cows. Flow cytometry was used to measure lymphocyte proliferation with the Ki67 antibody, and specific monoclonal antibodies were used to identify CD3, CD4, and CD8 T lymphocyte and CD21 B lymphocyte populations. The supernatant of the peripheral blood mononuclear cell culture was used to measure IL-17A and IFN-γ production. Two distinct, inactivated strains of bovine-associated Staphylococcus aureus [one causing a persistent intramammary infection (IMI) and the other from the nose], 2 inactivated Staphylococcus chromogenes strains [one causing an IMI and the other from a teat apex), as well as an inactivated Mammaliicoccus fleurettii strain originating from sawdust from a dairy farm, and the mitogens concanavalin A and phytohemagglutinin M-form (both specifically to measure lymphocyte proliferation) were studied. In contrast to the "commensal" Staph. aureus strain originating from the nose, the Staph. aureus strain causing a persistent IMI triggered proliferation of CD4⁺ and CD8⁺ subpopulations of T lymphocytes. The M. fleurettii strain and the 2 Staph. chromogenes strains had no effect on T- or B-cell proliferation. Furthermore, both Staph. aureus and Staph. chromogenes strains causing persistent IMI significantly increased IL-17A and IFN-γ production by peripheral blood mononuclear cells. Overall, multiparous cows tended to have a higher B-lymphocyte and a lower T-lymphocyte proliferative response than primiparous and nulliparous cows. Peripheral blood mononuclear cells of multiparous cows also produced significantly more IL-17A and IFN-γ. In contrast to concanavalin A, phytohemagglutinin M-form selectively stimulated T-cell proliferation.

A randomized controlled trial assessing the effect of intermittent and abrupt cessation of milking to end lactation on the well-being and intramammary infection risk of dairy cows

The objectives were to compare the effects of an intermittent milking schedule with a thrice daily milking schedule during the final week of lactation on the well-being, udder health, milk production, and risk of culling of dairy cows. We hypothesized that cows subjected to an intermittent milking schedule would experience less udder engorgement and pain, lower concentrations of fecal glucocorticoid metabolites (11,17-dioxoandrostanes; 11,17-DOA concentration) after dry-off, lower risk of an intramammary infection during the dry period, higher milk production and lower somatic cell count in the subsequent lactation, and lower culling risk compared with herd mates milked 3 times daily and dried off by abrupt cessation. In a randomized controlled field study, Holstein cows (n = 398) with a thrice daily milking schedule were assigned to treatment and control groups. The treatment consisted of an intermittent milking schedule for 7 d before dry-off (gradual cessation of milking, GRAD). Gradual-cessation cows were milked once daily until the day of dry-off, whereas cows in the control group (abrupt cessation of milking, APT) were milked 3 times daily until the day of dry-off. Udder firmness and pain responses of the udder 3 d after dry-off, as well as the percentage change in fecal 11,17-DOA concentration (3 d after dry-off compared with the dry-off day), were used to assess the well-being of the animals. Compared with cows in the GRAD group, the odds [95% confidence interval (CI)] of udder firmness were 1.55 (0.99-2.42) for cows in the APT group, and the odds of a pain response were 1.48 (0.89-2.44) for cows in the APT group. The least squares means (95% CI) of the percentage change in 11,17-DOA concentration were 129.3% (111.1-150.4) for the APT group and 113.6% (97.5-132.4) for the GRAD group. Quarter-level culture results from the periods before dry-off and after calving were compared, to assess the likelihoods of microbiological cure and new infection. Cows in the APT group had lower odds of a new intramammary infection in the dry period [odds ratio, 95% CI: 0.63 (0.37-1.05)], whereas we observed no meaningful differences in the microbiological cure likelihood among groups. The least squares means (95% CI) for somatic cell counts (log₁₀-transformed) were 4.9 (4.8-5.0) in the APT group and 4.9 (4.8-5.0) in the GRAD group. The odds (95% CI) of clinical mastitis in the first 30 d postcalving were 1.32 (0.53-3.30) in the APT group compared with the GRAD group. We observed no meaningful differences in milk production at the first test date postcalving or the culling risk among groups. We conclude that the gradual-cessation protocol tested herein failed to significantly improve animal well-being, udder health, milk production, and survival in the tested study cohort. However, the observed differences in udder firmness, as well as the numerical differences in udder pain and the percentage change in fecal 11,17-DOA concentrations suggest that this line of research may be useful. Future research is needed to develop drying-off strategies that are appropriate for lowering milk production at the end of the lactation and improve animal well-being without compromising udder health.

Genetic and Antimicrobial Resistance Profiles of Mammary Pathogenic E. coli (MPEC) Isolates from Bovine Clinical Mastitis

Mammary pathogenic E. coli (MPEC) is one of the main pathogens of environmental origin responsible for causing clinical mastitis worldwide. Even though E. coli are strongly associated with transient or persistent mastitis and the economic impacts of this disease, the virulence factors involved in the pathogenesis of MPEC remain unknown. Our aim was to characterize 110 MPEC isolates obtained from the milk of cows with clinical mastitis, regarding the virulence factor-encoding genes present, adherence patterns on HeLa cells, and antimicrobial resistance profile. The MPEC isolates were classified mainly in phylogroups A (50.9%) and B1 (38.2%). None of the isolates harbored genes used for diarrheagenic E. coli classification, but 26 (23.6%) and 4 (3.6%) isolates produced the aggregative or diffuse adherence pattern, respectively. Among the 22 genes investigated, encoding virulence factors associated with extraintestinal pathogenic E. coli pathogenesis, fimH (93.6%) was the most frequent, followed by traT (77.3%) and ompT (68.2%). Pulsed-field gel electrophoresis analysis revealed six pulse-types with isolates obtained over time, thus indicating persistent intramammary infections. The genes encoding beta-lactamases detected were as follows: bla_TEM (35/31.8%); bla_CTX-M-2/bla_CTX-M-8 (2/1.8%); bla_CTX-M-15 and bla_CMY-2 (1/0.9%); five isolates were classified as extended spectrum beta-lactamase (ESBL) producers. As far as we know, papA, shf, ireA, sat and bla_CTX-M-8 were detected for the first time in MPEC. In summary, the genetic profile of the MPEC studied was highly heterogeneous, making it impossible to establish a common genetic profile useful for molecular MPEC classification. Moreover, the detection of ESBL-producing isolates is a serious public health concern.

A longitudinal census of the bacterial community in raw milk correlated with Staphylococcus aureus clinical mastitis infections in dairy cattle

BACKGROUND

Staphylococcus aureus is a common cause of clinical mastitis (CM) in dairy cattle. Optimizing the bovine mammary gland microbiota to resist S. aureus colonization is a growing area of research. However, the details of the interbacterial interactions between S. aureus and commensal bacteria, which would be required to manipulate the microbiome to resist infection, are still unknown. This study aims to characterize changes in the bovine milk bacterial community before, during, and after S. aureus CM and to compare bacterial communities present in milk between infected and healthy quarters.

METHODS

We collected quarter-level milk samples from 698 Holstein dairy cows over an entire lactation. A total of 11 quarters from 10 cows were affected by S. aureus CM and milk samples from these 10 cows (n = 583) regardless of health status were analyzed by performing 16S rRNA gene amplicon sequencing.

RESULTS

The milk microbiota of healthy quarters was distinguishable from that of S. aureus CM quarters two weeks before CM diagnosis via visual inspection. Microbial network analysis showed that 11 OTUs had negative associations with OTU0001 (Staphylococcus). A low diversity or dysbiotic milk microbiome did not necessarily correlate with increased inflammation. Specifically, Staphylococcus xylosus, Staphylococcus epidermidis, and Aerococcus urinaeequi were each abundant in milk from the quarters with low levels of inflammation.

CONCLUSION

Our results show that the udder microbiome is highly dynamic, yet a change in the abundance in certain bacteria can be a potential indicator of future S. aureus CM. This study has identified potential prophylactic bacterial species that could act as a barrier against S. aureus colonization and prevent future instances of S. aureus CM.

Characterisation of Staphylococci Isolated from Milk Samples of a Water Buffalo Herd

Water buffalo produce a tenth of milk for global human consumption. Non-aureus staphylococci (NAS) are among the most commonly isolated bacteria from mastitis in water buffalo and dairy cows. These results described the initial characterisation of 17 NAS—15 Staphylococcus simulans and two Staphylococcus chromogenes from a water buffalo herd (n = 44) in South Africa. The isolates were identified by classical microbiology, MALDI-TOF, and 16S rRNA, and the disc diffusion method determined the antibiotic susceptibility. A multi-locus sequence typing scheme (MLST) was developed to determine S. simulans sequence types (ST), by defining and comparing seven housekeeping gene fragment sequences. Sequence typing confirmed all 15 S. simulans isolates from water buffalo which belonged to a single ST, genetically distant from the six bovine STs isolated from adjacent farms, which also varied, indicating no current bacterial transfer between species. The antibiotic resistance patterns of S. simulans varied between beta-lactams. The mean milk somatic cell count (SCC) for the water buffalo milk samples was 166,500 cells/mL milk. This information offers insights into the epidemiology and comparison among isolates from various origins, which leads to effective proactive mastitis strategies resulting in safe, high-quality dairy products from water buffalo and dairy cows for human consumption.

Genotypic characterization of mecA gene and antibiogram profile of coagulase-negative staphylococci in subclinical mastitic cows

Background and Aim:

Coagulase-negative staphylococci (CNS) are becoming the major cause of clinical and subclinical bovine mastitis around the world. This study aims to estimate the prevalence, antibiogram, and frequency of the methicillin-resistant (MR) (mecA) gene in CNS collected from cows with subclinical mastitis

Materials and Methods:

Thirty-four milk samples were collected from 20 cows. Fifteen subclinical mastitis samples (~44.12%) were identified as CNS isolates. The Vitek2 compact system method was employed for the identification of the species. Furthermore, antibiotic sensitivity tests were performed against 10 different antibiotics for CNS strains. The mecA gene from isolated CNS was detected by conventional polymerase chain reaction (PCR).

Results:

Staphylococcus haemolyticus was the most predominant isolated species with an incidence of 33.3% (5/15 isolates), followed by 26.7% for Staphylococcus sciuri and Staphylococcus vitamins (4/15 isolates), and 13.3% for Staphylococcus vitulinus (2/15 isolates), respectively. The highest resistance rates were determined to be 40% (6/15 isolates) against penicillin and oxacillin (OX), 33.3% (5/15 isolates) against clindamycin, 13% (2/15 isolates) against chloramphenicol, amoxicillin, and erythromycin, and 5% (1/15 isolates) against ciprofloxacin, respectively. The results revealed that the isolates were resistant to one or more antimicrobial agents, with five isolates displaying multiple antimicrobial resistance. Furthermore, the results exhibit that all CNS isolates had the mecA gene at 310 bp with a 100% frequency. Moreover, for detecting MR isolates, there are significant discrepancies between phenotypic and genotypic approaches, and only 6/15 CNS isolates phenotypically demonstrated OX resistance.

Conclusion:

The results emphasize the necessity of frequent monitoring of phenotypic and genotypic profiles of CNS isolates to ensure effective control measures and the prevention of multidrug resistance strain evolution.

Persistent Coagulase-Negative Staphylococcal Bacteremia in Neonates: Clinical, Microbiological Characteristics and Changes within a Decade

Atypical outbreaks of persistent coagulase-negative staphylococci (CoNS) bacteremias, defined as three or more consecutive positive blood cultures with the same CoNS species, at least 48 h apart, have been reported in neonatal intensive-care units (NICUs). Our aim was to describe the profile of these cases in our NICU over a two-year period with the objective of assessing possible changes within a decade. Demographics, clinical and microbiological data were recorded for all CoNS bacteremias in our tertiary NICU during 2016–2017 and compared with the results of the same study in 2006–2007. Fifty-six cases of CoNS sepsis were recorded. Fourteen (25%) of them were persistent. There were no significant differences in demographic and clinical characteristics between cases with persistent vs. non-persistent bacteremia. Staphylococcus epidermidis was the most common species. In logistic regression analysis, biofilm production (β = 2.464, p = 0.04) was the most significant determinant for the development of persistent CoNS bacteremia. Our isolates were less likely to produce biofilm and carry ica operon as compared to those of 2006–2007. The cases of persistent CoNS sepsis have decreased within a decade, which could be attributed to the implementation of intensive infection control practices. Biofilm production remains the most important risk factor.

Peptidomic changes in the milk of water buffaloes (Bubalus bubalis) with intramammary infection by non-aureus staphylococci

Mastitis by non-aureus staphylococci (NAS) is a significant issue in dairy buffalo farming. In a herd with subclinical NAS mastitis, we identified Staphylococcus microti as the predominant species. To assess milk protein integrity and investigate potential disease markers, we characterized 12 NAS-positive and 12 healthy quarter milk samples by shotgun peptidomics combining peptide enrichment and high-performance liquid chromatography/tandem mass spectrometry (LC–MS/MS). We observed significant changes in the milk peptidome. Out of 789 total peptides identified in each group, 49 and 44 were unique or increased in NAS-positive and healthy milk, respectively. In NAS-positive milk, the differential peptides belonged mainly to caseins, followed by milk fat globule membrane proteins (MFGMP) and by the immune defense/antimicrobial proteins osteopontin, lactoperoxidase, and serum amyloid A. In healthy milk, these belonged mainly to MFGMP, followed by caseins. In terms of abundance, peptides from MFGMP and immune defense protein were higher in NAS-positive milk, while peptides from caseins were higher in healthy milk. These findings highlight the impact of NAS on buffalo milk quality and mammary gland health, even when clinical signs are not evident, and underscore the need for clarifying the epidemiology and relevance of the different NAS species in this dairy ruminant.

The microbiome of common bedding materials before and after use on commercial dairy farms

Background

Bovine mastitis is one of the most economically important diseases affecting dairy cows. The choice of bedding material has been identified as an important risk factor contributing to the development of mastitis. However, few reports examine both the culturable and nonculturable microbial composition of commonly used bedding materials, i.e., the microbiome. Given the prevalence of nonculturable microbes in most environments, this information could be an important step to understanding whether and how the bedding microbiome acts as a risk factor for mastitis. Therefore, our objective was to characterize the microbiome composition and diversity of bedding material microbiomes, before and after use.

Methods

We collected 88 bedding samples from 44 dairy farms in the U.S. Unused (from storage pile) and used (out of stalls) bedding materials were collected from four bedding types: new sand (NSA), recycled manure solids (RMS), organic non-manure (ON) and recycled sand (RSA). Samples were analyzed using 16S rRNA sequencing of the V3–V4 region.

Results

The overall composition as well as the counts of several microbial taxa differed between bedding types, with Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes dominating across all types. Used bedding contained a significantly different microbial composition than unused bedding, but the magnitude of this difference varied by bedding type, with RMS bedding exhibiting the smallest difference. In addition, positive correlations were observed between 16S rRNA sequence counts of potential mastitis pathogens (bacterial genera) and corresponding bedding bacterial culture data.

Conclusion

Our results strengthen the role of bedding as a potential source of mastitis pathogens. The consistent shift in the microbiome of all bedding types that occurred during use by dairy cows deserves further investigation to understand whether this shift promotes pathogen colonization and/or persistence, or whether it can differentially impact udder health outcomes. Future studies of bedding and udder health may be strengthened by including a microbiome component to the study design.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-022-00171-2.

Dairy Cows’ Udder Pathogens and Occurrence of Virulence Factors in Staphylococci

Simple Summary

Dairy farmers and those involved in primary milk production face the challenge of maintaining the health of their animals. Although the level of technological support during milking has increased and appropriate veterinary measures are available, mastitis remains a major health problem in dairy cows as well as a major threat to dairy farm profitability. The results of this study indicate that, in addition to the major udder pathogens (S. aureus, S. uberis and S. agalactiae) causing dairy mastitis, non-aureus staphylococci (NAS) are a major risk to dairy cows during early lactation. NAS, such as S. chromogenes, S. warneri and S. xylosus, which were isolated from animals with clinical mastitis characterized by mild, moderate, or severe symptoms and persistent infections, had the highest representation of virulence factors (production of hemolysis, gelatinase and biofilm; the ability to hydrolyze DNA; resistance to antibiotics) in comparison to less virulent strains. In addition, isolates S. aureus and NAS showed resistance to one or more antimicrobials in 77.2%, and in 16 (11.7%) isolates, multi-drug resistance to three or more antimicrobial classes was confirmed. Due to the high resistance to β-lactam-antibiotics in two isolates of S. aureus and two species of NAS, the presence of a methicillin-resistant gene, mecA, was confirmed, which potentially poses serious complications for the treatment of dairy cows and a serious health risk to milk consumers.

Abstract

This study investigated 960 Slovak and Czech spotted cattle from four different conventional (non-organic) dairy herds located in Eastern Slovakia and Czechia during early lactation (14–100 days after calving). Dairy cows were examined clinically; milk from fore-stripping of each udder quarter was subjected to sensory examination and assessed by the California mastitis test (CMT), and laboratory analyses of bacterial pathogens in milk, including virulence factors, were conducted. Positive CMT scores (1–3) for one or more quarters were detected in 271 (28.2%) of the examined animals. Out of 230 infected milk samples, representing 24.0% of all dairy cows, staphylococci (59.1% of positive findings) were the most commonly isolated organisms, followed by E. coli (11.3%), streptococci Str. uberis (9.1%) and Str. agalactiae (3.4%), and enterococci (6.1%). From 136 isolates of S. aureus (38 isolates) and non-aureus staphylococci (NAS; 98 isolates), virulence factors and their resistance to 14 antimicrobials were detected using the disk diffusion method, with PCR detection of the methicillin resistance gene, mecA. An increased incidence of clinical and chronic forms of mastitis has been reported in mastitic cows in which staphylococci, especially S. aureus and NAS (S. chromogenes, S. warneri, and S. xylosus), have been detected and compared to other isolated udder pathogens. From those species, S. aureus and isolates of NAS mentioned above showed multiple virulence factors that are more likely to hydrolyze DNA, hemolysis, produce gelatinase and biofilm, and have multi-drug resistance as compared to other less virulent staphylococci. Generally, the isolated staphylococci showed 77.2% resistance to one or more antimicrobials, in particular to aminoglycosides, β-lactams, macrolides, or cephalosporins. Isolates that showed the ability to form a biofilm were more resistant to more than one antimicrobial than isolates without biofilm production. Multi-drug resistance to three or more antimicrobial classes was recorded in 16 isolates (11.7%), and the presence of the mecA gene was also confirmed in two isolates of S. aureus and two species of NAS.

SxsA, a novel surface protein mediating cell aggregation and adhesive biofilm formation of Staphylococcus xylosus

Biofilm formation of staphylococci has been an emerging field of research for many years. However, the underlying molecular mechanisms are still not fully understood, and vary widely between species and strains. The aim of this study was to identify new effectors impacting biofilm formation of two Staphylococcus (S.) xylosus strains. We identified a novel surface protein conferring cell aggregation, adherence to abiotic surfaces and biofilm formation. The S. xylosus surface protein A (SxsA) is a large protein occurring in variable sizes. It lacks sequence similarity to other staphylococcal surface proteins but shows similar structural domain organization and functional features. Upon deletion of sxsA, adherence of S. xylosus strain TMW 2.1523 to abiotic surfaces was completely abolished, and significantly reduced in TMW 2.1023. Macro- and microscopic aggregation assays further showed that TMW 2.1523 sxsA mutants exhibit reduced cell aggregation compared to the wildtype. Comparative genomic analysis revealed that sxsA is part of the core genome of S. xylosus, S. paraxylosus and S. nepalensis and additionally encoded in a small group of S. cohnii and S. saprophyticus strains. This study provides insights into protein-mediated biofilm formation of S. xylosus and identifies a new cell wall-associated protein influencing cell aggregation and biofilm formation.

Mammaliicoccus spp. from German Dairy Farms Exhibit a Wide Range of Antimicrobial Resistance Genes and Non-Wildtype Phenotypes to Several Antibiotic Classes

Simple Summary

Worldwide, antimicrobial resistance (AMR) is of major concern for human and animal health since infections with multidrug-resistant bacteria are often more challenging and costly. In the family Staphyloccocaceae, the species Staphylococcusaureus in particular was reported to cause severe infections. Although most of the other Staphylococcaceae members were not shown to cause severe illnesses, the transmission of AMR genes to harmful species might take place. Therefore, the monitoring of AMR potential in different environments is of high relevance. Mammaliicocci on dairy farms might represent such an AMR gene reservoir. Thus, in this study, the AMR potential of mammaliicocci isolates from German dairy farms was investigated. Whole-genome sequencing (WGS) of the isolates was conducted to evaluate the phylogenetic relationship of the isolates and analyze AMR genes. In addition, antimicrobial susceptibility testing was performed to compare the AMR genotype with the phenotype. It turned out that mammaliicocci may harbor large numbers of different AMR genes and exhibit phenotypic resistance to various antibiotics. Since some AMR genes are likely located on mobile genetic elements, such as plasmids, AMR gene transmission between members of the Staphylococcaceae family might occur.

Abstract

Mammaliicocci might play a major role in antimicrobial resistance (AMR) gene transmission between organisms of the family Staphylococcaceae, such as the potentially pathogenic species Staphylococcus aureus. The interest of this study was to analyze AMR profiles of mammaliicocci from German dairy farms to evaluate the AMR transmission potential. In total, 65 mammaliicocci isolates from 17 dairy farms with a history of MRSA detection were analyzed for AMR genotypes and phenotypes using whole genome sequencing and antimicrobial susceptibility testing against 19 antibiotics. The various genotypic and phenotypic AMR profiles of mammaliicocci from German dairy farms indicated the simultaneous occurrence of several different strains on the farms. The isolates exhibited a non-wildtype phenotype to penicillin (58/64), cefoxitin (25/64), chloramphenicol (26/64), ciprofloxacin (25/64), clindamycin (49/64), erythromycin (17/64), fusidic acid (61/64), gentamicin (8/64), kanamycin (9/64), linezolid (1/64), mupirocin (4/64), rifampicin (1/64), sulfamethoxazol (1/64), streptomycin (20/64), quinupristin/dalfopristin (26/64), tetracycline (37/64), tiamulin (59/64), and trimethoprim (30/64). Corresponding AMR genes against several antimicrobial classes were detected. Linezolid resistance was associated with the cfr gene in the respective isolate. However, discrepancies between genotypic prediction and phenotypic resistance profiles, such as for fusidic acid and tiamulin, were also observed. In conclusion, mammaliicocci from dairy farms may carry a broad variety of antimicrobial resistance genes and exhibit non-wildtype phenotypes to several antimicrobial classes; therefore, they may represent an important source for horizontal gene transfer of AMR genes to pathogenic Staphylococcaceae.

Whole Genome Sequencing of Staphylococci Isolated From Bovine Milk Samples

Staphylococci are among the commonly isolated bacteria from intramammary infections in bovines, where Staphylococcus aureus is the most studied species. This species carries a variety of virulence genes, contributing to bacterial survival and spread. Less is known about non-aureus staphylococci (NAS) and their range of virulence genes and mechanisms, but they are the most frequently isolated bacteria from bovine milk. Staphylococci can also carry a range of antimicrobial resistance genes, complicating treatment of the infections they cause. We used Illumina sequencing to whole genome sequence 93 staphylococcal isolates selected from a collection of staphylococcal isolates; 45 S. aureus isolates and 48 NAS isolates from 16 different species, determining their content of antimicrobial resistance genes and virulence genes. Antimicrobial resistance genes were frequently observed in the NAS species as a group compared to S. aureus. However, the lincosamide resistance gene lnuA and penicillin resistance gene blaZ were frequently identified in NAS, as well as a small number of S. aureus. The erm genes conferring macrolide resistance were also identified in several NAS isolates and in a small number of S. aureus isolates. In most S. aureus isolates, no antimicrobial resistance genes were detected, but in five S. aureus isolates three to six resistance genes were identified and all five of these carried the mecA gene. Virulence genes were more frequently identified in S. aureus, which contained on average five times more virulence genes compared to NAS. Among the NAS species there were also differences in content of virulence genes, such as S. chromogenes with a higher average number of virulence genes. By determining the content of a large selection of virulence genes and antimicrobial resistance genes in S. aureus and 16 different NAS species our results contribute with knowledge regarding the genetic basis for virulence and antimicrobial resistance in bovine staphylococci, especially the less studied NAS. The results can create a broader basis for further research into the virulence mechanisms of this important group of bacteria in bovine intramammary infections.

Spatio-Temporal Variation in the Prevalence of Major Mastitis Pathogens Isolated From Bovine Milk Samples Between 2008 and 2017 in Ontario, Canada

An understanding of the spatio-temporal distribution of several groups of mastitis pathogens can help to inform programs for the successful control and management of mastitis. However, in the absence of an active surveillance program such information is not readily available. In this retrospective study we analyzed passive surveillance data from a diagnostic laboratory with an aim to describe the spatio-temporal trend of major mastitis pathogens between 2008 and 2017 in Ontario dairy cattle. Data for all milk culture samples submitted to the Animal Health Laboratory (AHL) at the University of Guelph between 2008 and 2017 was accessed. Descriptive analyses were conducted to identify the major pathogens and Chi-square goodness-of-fit tests were used to compare between multiple proportions. Likewise, univariable logistic regression analysis was performed to determine if there was a change in the probability of isolating the major mastitis pathogens depending on geography or time. Seasonality was assessed by calculating the seasonal relative risk (RR). Of a total of 85,979 milk samples examined, more than half of the samples (61.07%) showed no growth and the proportion of samples that showed no growth almost halved during the study period. Of the samples (36.21%, n = 31,133) that showed any growth, the major bacterial pathogens were Staphylococcus aureus (15.60%), Non-aureus Staphylococci (NAS) (5.04%), Corynebacterium spp. (2.96%), and Escherichia coli (2.00%). Of the NAS, the major species reported were Staphylococcus chromogenes (69.02%), Staphylococcus simulans (14.45%), Staphylococcus epidermidis (12.99%), and Staphylococcus hyicus (2.13%). A temporal change in the prevalence of contagious pathogens like S. aureus and Corynebacterium spp. was observed with an increasing odds of 1.06 and 1.62, respectively. Likewise, except for Trueperella pyogenes, the prevalence of all the major environmental mastitis pathogens increased during the study period. The isolation of most of the pathogens peaked in summer, except for S. aureus, T. pyogenes, and Streptococcus dysgalactiae which peaked in spring months. Interestingly, a regional pattern of isolation of some bacterial pathogens within Ontario was also observed. This study showed a marked spatio-temporal change in the prevalence of major mastitis pathogens and suggests that a regional and seasonal approach to mastitis control could be of value.

Secondary Staphylococcus aureus intramammary colonization is reduced by non-aureus staphylococci exoproducts

Non-aureus staphylococci (NAS) and Staphylococcus aureus are pathogens that cause bovine mastitis, a costly disease for dairy farmers, however; many NAS are considered part of the normal udder microbiota. It has been suggested that through a mechanism that remains to be elucidated, NAS intramammary colonization can prevent subsequent infection with other bacterial pathogens. This study shows that in a murine mastitis model, secondary Staph. aureus intramammary colonization is reduced by exoproducts from Staph. chromogenes and Staph. simulans, both NAS, while Streptococcus spp. exoproducts have much less ability to affect the course of the infection caused by S. aureus.