Prevalence, antimicrobial susceptibility profiles and resistant gene identification of bovine subclinical mastitis pathogens in Bangladesh

Subclinical mastitis (SCM), a silent threat in the dairy sector of Bangladesh poses a significant economic impact and serves as a potential source of infection for healthy cows, hindering efforts to achieve milk self-sufficiency. Despite the importance of this issue, limited research has been conducted on mastitis in Sylhet region of Bangladesh. This study aimed to investigate the molecular prevalence, antimicrobial susceptibility profile and resistant genes detection on pathogens (Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae) causing SCM. In a cross-sectional study utilizing convenience sampling, 325 milk samples were collected from apparently healthy dairy cows. Initially, SCM was detected using the modified Whiteside test (MWST) method. Suspected positive samples were then subjected to bacteriological culture and standard biochemical assays, followed by molecular identification through polymerase chain reaction (PCR). Finally, antimicrobial susceptibility testing was conducted on all PCR-positive samples using the Kirby-Bauer disk diffusion method on Mueller-Hinton agar. In the Sylhet district, the prevalence of SCM was 64.92 % (211 out of 325) at the individual animal level and 82.69 % (43 out of 52) at the herd level. Among the SCM-positive animals, S. aureus was found in 31.75 % (67 out of 211) of cases, E. coli in 81.99 % (173 out of 211), and K. pneumoniae in 66.82 % (141 out of 211). K. pneumoniae had the highest prevalence at 60 % in Zakiganj, S. aureus at 45 % in Zakiganj, and E. coli at 72 % in Bishwanath Upazila. Extended spectrum beta lactamase (ESBL) genes blaTEM, blaOXA, blaCTX-M1, blaCTX-M2, MultiCaseDHA were identified. Additionally, antibiotic resistance genes tet(A), AAC(3)-iv, and Sul1 were also detected. The pathogens exhibited resistance to Penicillins (ampicillin, amoxicillin), Cephems (cefuroxime, ceftazidime), and Tetracyclines (tetracycline). However, all three bacteria were highly sensitive to meropenem, amikacin, gentamicin, ciprofloxacin, and sulfamethoxazole-trimethoprim. These findings highlight the critical need for targeted antimicrobial stewardship and effective control measures to mitigate the impact of SCM on dairy production and animal health in the Sylhet region of Bangladesh.