Methicillin-resistant Staphylococcus aureus (MRSA) associated with mastitis among water buffaloes in the Philippines

Evidence of vancomycin-resistant Staphylococcus aureus, multidrug-resistant S. aureus, and Enterococcus faecium-causing mastitis in Thailand and Cambodia

Background and Aim

Bovine mastitis, an inflammatory condition of the mammary gland, is a critical economic issue in the dairy industry. Antimicrobial resistance (AMR) to mastitis-causing pathogens poses a significant threat to dairy operations in Thailand and Cambodia. This study investigates the AMR of mastitis pathogens in Thailand and Cambodia. It focuses on detecting methicillin-resistant Staphylococcus aureus, vancomycin-resistant S. aureus (VRSA), and vancomycin-resistant enterococci by identifying the presence of mecA, vanA, and vanB genes in bacterial isolates.

Materials and Methods

A total of 65 bacterial isolates (55 S. aureus from Thailand and 10 Enterococcus faecium from Thailand and Cambodia) were analyzed. Disk diffusion tests were conducted for antibiotic susceptibility, and polymerase chain reaction was employed to detect AMR genes.

Results

S. aureus isolates showed resistance to penicillin (21.8%), tetracycline (9.1%), and gentamycin (7.3%). Three isolates were identified as multidrug-resistant (MDR), resistant to tetracycline, gentamycin, and penicillin. E. faecium isolates exhibited high resistance to tetracycline (100%) and penicillin (90%), with 60% classified as MDR. Phenotypic analysis identified VRSA in 11% of S. aureus isolates. However, mecA, vanA, and vanB genes were not detected in any isolate.

Conclusion

Mastitis pathogens in this study pose significant AMR challenges, especially with MDR S. aureus and E. faecium, and phenotypically VRSA without the vanA gene. The findings highlight the need for judicious antibiotic use in dairy farms and further studies with broader sampling.

Prevalence, Cross Contamination, Virulence, and Multidrug Resistance Profiles of Staphylococcus aureus Isolates from Four Middle-Scale Dairy Farms in Bareilly, Northern India

Milk, a nutritious global important food commodity, serves as an excellent medium for microbial growth as well. The foodborne pathogen Staphylococcus aureus is a commensal member of human microflora that enters the food chain through poor hygienic practices and cross contamination and causes various clinical manifestations in humans. During this study, raw milk and swab samples (milker's hand, udder, towel, milking bucket, and farm floor) were collected from four middle-scale buffalo dairy farms. The results revealed S. aureus presence in 11.6% (n = 56/448) bucket raw milk samples and 2.6% (n = 12/448) udder raw milk samples. Contrarily, S. aureus prevalence was significantly higher in farm floors (100%, n = 84/84), towel (35.7%, n = 10/28), milking bucket (11.6%, n = 56/448), milker's hand (10.7%, n = 3/28), and udder swab samples (4.0%, n = 18/448). The chi-square test yielded p values of 0.000, 0.005, and 0.0011 for udder raw milk, udder swab, and milker's hand swab, respectively. The p values of the milking bucket (p = 0.048) and farm floors (p = 0.0183) confirmed their possible role in S. aureus cross contamination. Gene amplifications of nuclease and enterotoxin A indicate potential virulence of S. aureus isolates in collected samples. Antibiotic susceptibility testing revealed multidrug resistance in 44% (n = 239) of S. aureus isolates with the highest resistance of 61% against penicillin. Resistance against ampicillin, streptomycin, and lincomycin was observed. Fewer S. aureus isolates were resistant to kanamycin and erythromycin, whereas the lowest number of resistant isolates was observed against chloramphenicol. A high prevalence of S. aureus in the farm environment and milking equipment suggested the cross contamination of potentially enterotoxin-producing and multidrug-resistant S. aureus to raw milk. Therefore, good hygiene practices should be enforced to avoid foodborne and zoonotic infections.

Molecular characteristics of Staphylococcus aureus strains isolated from subclinical mastitis of water buffaloes in Guangdong Province, China

Intramammary infections (IMI) in animals reared for milk production can result in large economic losses and distress to the animals. Staphylococcus aureus is an important causative agent of IMI in dairy cows, but its prevalence in water buffaloes has not been determined. Therefore, the current study was conducted to investigate the prevalence of subclinical mastitis in water buffaloes and the antimicrobial susceptibility, virulence genes and biofilm formation abilities of Staphylococcus aureus isolates recovered from water buffaloes in Guangdong, China. Staphylococcus aureus strains were isolated from milk samples of water buffaloes with subclinical mastitis, and twofold microdilution, PCR and crystal violet staining methods were used to determine antimicrobial susceptibility, distributions of virulence and antimicrobial resistance genes and biofilm formation ability, respectively. Our results indicated that 29.44% of water buffaloes were diagnosed with subclinical mastitis, and the most prevalent pathogens were Escherichia coli (96.17%), coagulase-negative staphylococci (CoNS) (67.60%) and S. aureus (28.57%). Most S. aureus isolates showed resistance to bacitracin, doxycycline, penicillin, florfenicol, and tetracycline but were susceptible to ciprofloxacin, ceftizoxime, cefoquinoxime, and ofloxacin. Moreover, 63.72% of S. aureus isolates were positive for tetM, and the prevalence of msrB, blaZ, mecA, fexA, and tetK ranged from 21.24 to 6.19%. All S. aureus isolates harbored clfB and icaA genes, and the virulence genes hla (93.8%), hld (91.15%), clfA (90.27%), fnbA (86.73%), and hlb (83.19%), and tsst, icaD, sec, see, fnbB, and sea showed a varied prevalence ranging from 3.5 to 65.49%. All S. aureus isolates possessed the ability to form biofilms, and 30.09% of isolates showed strong biofilm formation abilities, while 19.47% of isolates were weak biofilm producers. Our results indicated that subclinical mastitis is prevalent in water buffaloes in Guangdong, China, and S. aureus is prevalent in samples from water buffaloes with subclinical mastitis. Most S. aureus isolates were susceptible to cephalosporins and fluoroquinolones; thus, ceftizoxime and cefoquinoxime can be used to treat subclinical mastitis in water buffaloes.

Genetic and Phenotypic Characterization of Subclinical Mastitis-Causing Multidrug-Resistant Staphylococcus aureus

The core objective of this study was to genetically and phenotypically characterize subclinical mastitis-causing multidrug-resistant Staphylococcus aureus (MDRSA). In addition, risk factors associated with subclinical mastitis caused by MDRSA were investigated. Bacterial cultures were performed on 2120 mammary quarters, 40 swabs of milk utensils, 5 bulk tank milk samples, and 11 nostril and 11 hand swabs from milkers from five dairy farms. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was conducted for S. aureus identification. Antimicrobial resistance was screened phenotypically using the disk diffusion test in all S. aureus isolates. A biofilm formation assay; detection of genes associated with beta-lactam resistance, efflux pump, and biofilm formation; and pulsed-field gel electrophoresis (PFGE) were performed in all MDRSA isolates. Multi-locus sequence typing (MLST) was carried out in cefoxitin-resistant MDRSA isolates. A total of 188 S. aureus isolates from milk as well as two from milking utensils and one from bulk tank milk were identified. Most of the isolates (92.7%; 177 of 191) showed beta-lactam resistance, and 7% (14 of 191) were MDRSA. Interestingly, 36% (5 of 14) of MDRSA isolates were cefoxitin-resistant, but none carried mecA or mecC genes. Based on PFGE results, it was observed that S. aureus strains were more likely to be unique to a specific herd. Two clonal complexes were identified, CC97 (ST126; commonly livestock-associated) and CC1 (ST7440; usually community-associated). To the best of our knowledge, this is the first report of ST7440 isolated from bovine mastitis in Brazil. The risk factor results underscored the importance of considering parity, stage of lactation, SCC, milk production, and herd size when studying the risk of subclinical mastitis and antimicrobial resistance in S. aureus. Thus, to implement effective strategies to prevent subclinical mastitis in dairy herds and to minimize MDRSA spread, it is important to understand MDRSA strains' distribution and their antimicrobial resistance profile.

Methicillin-resistant Staphylococcus aureus isolates derived from humans and animals in Yogyakarta, Indonesia

Background and Aim

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) as a highly pathogenic strain in veterinary and human medicine is a growing global problem. This study aimed to evaluate MRSA isolates of human and animal origin against various antibiotics in Yogyakarta, Indonesia.

Materials and Methods

The susceptibility test was carried out by the disk diffusion method using Mueller-Hinton agar against nine antibiotic disks. Methicillin-resistant S. aureus strains were genetically confirmed through mecA gene detection encoding for methicillin resistance by polymerase chain reaction.

Results

All 240 S. aureus strains isolated from animals and humans were resistant to penicillin G (P) (100% and 99%, respectively), followed by ampicillin (AMP), amoxicillin (AML), oxacillin (OX), erythromycin (E), clindamycin (DA), tetracycline (TE), gentamicin (GEN), and ciprofloxacin (CIP). Eighty-three MRSA strains were resistant to OX (100%), P (100%), AMP (99.27%), AML (95.52%), E (87.77%), TE (71.33%), DA (63.24%), GEN (38.81%), and CIP (26.87%).

Conclusion

The antimicrobial resistance pattern of S. aureus human isolates was similar to their animal counterpart, with 77.20% of MRSA strains classified as multidrug-resistant (MDR) bacteria. These findings indicate an increase in MDR S. aureus strains of animal origin in Yogyakarta, thus raising public health concerns about MRSA zoonotic spread.

Changes in the lipidome of water buffalo milk during intramammary infection by non-aureus Staphylococci

This study aimed to determine the lipidome of water buffalo milk with intramammary infection (IMI) by non-aureus staphylococci (NAS), also defined as coagulase-negative staphylococci, using an untargeted lipidomic approach. Non-aureus Staphylococci are the most frequently isolated pathogens from dairy water buffalo milk during mastitis. A total of 17 milk samples from quarters affected by NAS-IMI were collected, and the lipidome was determined by liquid chromatography-quadrupole time-of-flight mass spectrometry. The results were compared with the lipidome determined on samples collected from 16 healthy quarters. The study identified 1934 different lipids, which were classified into 15 classes. The abundance of 72 lipids changed in NAS-IMI milk compared to healthy quarters. Significant changes occurred primarily in the class of free fatty acids. The results of this study provided first-time insight into the lipidome of dairy water buffalo milk. Moreover, the present findings provide evidence that NAS-IMI induces changes in water buffalo milk's lipidome.

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.

Exposure of Buffalo Milkers to Pathogenic Bacteria and Characterization of Isolated Methicillin-Resistant Staphylococcus spp

The research was focused on the surveillance of the exposure of buffalo milkers in contact with both animals and potentially contaminated equipment, pointing attention on the diffusion of antibiotic-resistant Staphylococcus spp. The monitoring was performed for 12 months, allowing the collection of 600 raw milk and buffalo udder surface samples, 192 milking lanes, 400 milking clusters, 160 personal protective equipment (PPEs) and electronic devices surface samples in contact with the workers of four milking parlors located in Southern Italy. The analysis of the milk samples evidenced the highest exposure to the bacteria considered (and mainly to S. aureus) from late winter-spring seasons onward. The possible risk arising from buffalo udder, milking clusters, and lines were instead considered rather stable along the entire period of sampling. The PPEs turned out to be a source of contamination for milkers mainly during the spring and summer periods. The analysis for oxacillin/methicillin resistance revealed in all the farms enrolled an overall amount of 37.5% of Staphylococci strains (belonging to S. aureus, S. haemolyticus, S. pseudintermedius, S. chromogenes species) resistant both to methicillin and oxacillin. The investigation demonstrated that the potential transfer of pathogenic bacteria to humans would have a better chance to occur at milk resumption time (since late winter-spring onward) when the number of animals to be milked is greater and the activity in the milking parlor is more challenging. At the same time, the findings seem to point out that the potential risk may be worsened by a significant presence of oxacillin/methicillin-resistant Staphylococci, potentially resulting from irrational use of antibiotics.