Bacterial pathogens associated with subclinical mastitis in dairy cows: Distribution, antimicrobial resistance, and biofilm characteristics
INTERNATIONAL DAIRY JOURNAL, cilt.184, 2027 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 184
- Basım Tarihi: 2027
- Doi Numarası: 10.1016/j.idairyj.2026.106860
- Dergi Adı: INTERNATIONAL DAIRY JOURNAL
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, BIOSIS, Compendex, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Erciyes Üniversitesi Adresli: Evet
Özet
This cross-sectional study aimed to characterize Gram-positive bacterial pathogens associated with bovine subclinical mastitis by integrating species distribution, antimicrobial resistance, multidrug resistance (MDR), biofilm-forming capacity, and selected virulence-associated genes in Staphylococcus aureus. A total of 500 California Mastitis Test (CMT)-positive composite milk samples were collected from lactating cows across 42 dairy farms, excluding animals with clinical mastitis or recent antimicrobial treatment. Bacterial identification and antimicrobial susceptibility testing were performed using the PhoenixTM automated system, biofilm formation was evaluated using the microtiter plate method, and selected virulence- and resistance-associated genes in S. aureus were detected by PCR. Gram-positive mastitis-associated bacteria were recovered from 340 of 500 milk samples (68.0%), yielding 399 isolates. Among these isolates, S. aureus was the predominant species (32.1%), followed by S. agalactiae (12%), S. chromogenes and S. dysgalactiae (10% each), E. faecalis (8.8%), and S. simulans (8%). All S. aureus isolates were positive for nuc and femA, while mecA, sec, sed, and tst-1 were detected at low frequencies (3.9%, 3.1%, 2.3%, and 1.6%, respectively). Biofilm formation was observed in 56.1% of isolates, with the highest positivity in S. epidermidis (90%) and S. chromogenes (87.5%), which also exhibited the highest rates of strong biofilm formation (40% and 37.5%, respectively). Both biofilm positivity and category distributions differed significantly among species (p < 0.001). Antimicrobial resistance varied significantly among bacterial species (p < 0.001), with particularly high tetracycline resistance in S. simulans (93.8%), E. faecium (92.9%), E. faecalis (91.4%), and S. dysgalactiae (90.0%). S. aureus exhibited notable resistance to tetracycline and streptomycin (68.8% each), ampicillin (67.9%), and penicillin (64.1%). Overall, multidrug resistance was detected in 32.3% of isolates, with the highest prevalence in S. agalactiae (54.2%), and differed significantly among species (p = 0.037). These findings demonstrate considerable species-level variation in biofilm-forming capacity and antimicrobial resistance among Gram-positive bacteria associated with bovine subclinical mastitis and provide an integrated phenotypic and molecular characterization relevant to surveillance and herdlevel mastitis control.