Antimicrobial susceptibility testing was performed on a total of 253 [203 shiga toxinproducing Escherichia coli (STEC) and 50 non-STEC] Escherichia coli isolates from different raw meats, RTE meat foods, drinking water and human diarrhoeic samples in Punjab,India. Among the 20 antimicrobial agents tested, resistance was most frequent for penicillin (253/253, 100%) followed by linezolid (249/253, 98.4%), erythromycin(245/253, 96.8%), streptomycin (232/253, 91.7%), tetracycline (223/253, 88.1%), ampicillin 123/253,48.2%), cephotaxime (106/253,41.9%), trimethoprim (93/253, 36.8%)), co-trimoxazole (85/253, 33.6%), cefaclor (84/253, 33.2%), amoxycillin (79/253, 31.3%), ciprofloxacin (78/253, 30.8%), kanamycin (76/253, 30.0%), norfloxacin (62/253, 24.5%),ofloxacin (60/253, 23.7%), chloramphenicol (35/253, 13.8%), Polymyxin-B (27/253, 10.6%), colistin (25/253,9.9%), amikacin (22/253, 8.7%) and gentamycin (17/253, 6.7%).Out of 203 STEC isolates 73 (35.9%) showed resistance to more than 50% of the antibiotics tested. Only one isolate from pork showed resistance to 90% of the antibiotics tested. Cluster analysis also revealed that human isolates were different from other E. coli isolated from meat and meat products sources. The distribution of resistance determinants for tetracycline and streptomycin was assessed by PCR in resistant isolates.The most common resistance determinants were tetA (60%) and tetB (27%). Forty seven per cent of the isolates contained both strA and strB genes, 33% and 10% isolates carried strA and strB genes, respectively and 10% of isolates did carry neitherstrA nor strB. Cloning and sequencing of tetA and tetB genes of O69 shiga toxin-producing E. coli isolate from buffalo meat showed 99-100% homology with published sequences of related isolates in GenBank. Antibiotic susceptibility studies revealedthat meat, RTE meat products, drinking water and human diarrhoeic samples from Punjab, India contains multiple drug resistant strains of E. coli which may serve as areservoir for antibiotic resistance genes in the food environment and may transmit to humans through food chain.
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