Assessment of antibiotic resistant profile of coliform and Staphylococcus spp. isolated from milk from Kathmandu valley

Antimicrobial resistance (AMR) among milk pathogens is increasing, which is a serious threat to consumers’ health. Therefore, this study aims to assess the current antibiotic profile of coliforms and Staphylococcus spp. in milk samples. For this, thirty milk samples were collected from various locations in Kathmandu district. Isolation and enumeration were done on selective media using streak-plate and pour-plate techniques, respectively. Antibiotic susceptibility testing (AST) was done by the Kirby-Bauer disk diffusion method. A total of 48 bacteria were isolated, of which 31 were coliform and 17 Staphylococcus spp. Among the coliforms, Klebsiella spp. (n=17, 54.84%) was the most predominant in both raw (n=12, 70.6%) and pasteurized milk (n=5, 29.4%), followed by E. coli and Citrobacter spp. While for Staphylococcus spp., 15 (88.24%) were S. aureus and 2 (11.76%) were coagulase negative Staphylococcus (CONS). S. aureus was dominant in raw milk (n=13) rather than pasteurized milk (n=2). The AST of coliforms showed higher resistance towards ampicillin (96.75%), followed by cefoxitin, ciprofloxacin, nalidixic acid, nitrofurantoin, piperacillin, co-trimoxazole, ceftriaxone, chloramphenicol, and amikacin in descending order. In the case of S. aureus, higher resistance was observed for penicillin G (100.00%), followed by cefoxitin, ampicillin, ceftriaxone, tetracycline, ciprofloxacin, and amikacin. Further, 12 (70.53%) S. aureus were confirmed as methicillin-resistant S. aureus (MRSA). And a total of 10 (32.25%) coliforms and 9 (52.95%) S. aureus were identified as multiple drug resistant (MDR) strains. Thus, it can be concluded that antibiotic resistance among milk isolates of the coliform and Staphylococcus spp. is highly prevalent, and these can be a potential source of incurable milk-borne infections. Thus, routine assessment of microbial quality as well as AMR surveillance should be done on milk isolates to ensure the safety of consumer’s health.