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.

Automated summary

This study investigates the diversity and antimicrobial resistance of Staphylococcus species causing sub-clinical mastitis in dairy herds in Bangladesh. The most predominant species identified were S. chromogenes, S. epidermidis, S. haemolyticus, S. aureus, and S. sciuri. High levels of antimicrobial resistance were observed, and multi-drug resistance isolates were identified in all five species. Several risk factors for SCM caused by different species were also identified, including age, lactation stage, udder condition, use of antimicrobials, and history of previous clinical mastitis.