Evaluation of extended-spectrum β-lactamase production and plasmid-mediated quinolone resistance in Escherichia coli isolated from raw milk

This study aimed to determine the antibiotic resistance and extended-spectrum beta-lactamase production profiles of Escherichia coli isolates obtained from raw milk samples. To this end, the study used a chromogenic-based culture method, MALDI-TOF-MS, 16S rRNA gene sequencing, disc diffusion, and combined disc techniques. PCR was also performed to detect ESBL (blaSHV, blaTEM, and blaCTX-M), quinolone (qnrA, qnrB, and qnrS) genes, and the presence of class I integrons. A total of 47 (78.33%) E. coli isolates were identified by morphological, biochemical, and molecular tests. All isolates exhibited susceptibility to gentamicin and tobramycin. Resistance rates to different antibiotics were observed as follows: ampicillin, 51.06%; nalidixic acid, 23.40%; trimethoprim/ sulfamethoxazole, 17.02%; meropenem, 14.89%; ceftazidime, 8.51%; cefotaxime, 8.51%; piperacillintazobactam, 4.25%; aztreonam, 4.25%; imipenem, 4.25%; and levofloxacin, 2.12%. ESBL production was positive in 3 (6.38%) of the isolates. Bla genes were detected in 11 isolates (blaSHV = 9 [19.14%], blaTEM = 4 [8.5%], and blaCTX = 3 [6.38%]). The qnrB, qnrS, and qnrA genes were found in 5 (10.63%), 4 (8.51%), and 1 (2.12%) isolates, respectively. The intI1 gene was detected in 14 (29.78%) isolates.