Investigation of prevalence and antibiotic resistance profile of extended spectrum beta-lactamase-producing enterobacteriaceae in raw milk samples

Extended spectrum beta-lactamases (ESBL) are the enzymes that hydrolyze modern beta-lactam antibiotics such as penicillins, cephalosporins, monobactams and aztreonam. The increasing prevelance of ESBL-producing Gram negativebacteria has become a problem worldwide for food safety and public health. The objective of this study wasto investigate the prevalence of ESBL-producing Enterobacteriaceaein a total of 135 raw milk samples collected from Istanbul and the surrounding districts. After pre-enrichment in Enterobacteriaceae Enrichment broth and selectıve enrichment on a chromogen ESBL media, the colonies were subcultured onto Trypton Soy agar for purification. The purified isolates were initially exposed to oxidase testing. Subsequently, the oxidase negative ones were selected and identified by using mass spectrometer (Vitek® MS, bio Meriux). The characterized ESBL suspected strains were screened for ESBL-production by ceftazidime (CAZ), cefotaxim (CTX), and cefpodoxime (CPD) dıscs respectively. The ESBL-suspected isolates were confirmed with a combination of ceftazidime (CAZ), cefotaxim (CTX), and cefpodoxime (CPD ± clavulanate (CV)discs based on combined disc-diffusion testing. Following that, the final confirmation of ESBL-production wthin the isolates were performed following the instructions of Merlin Micronaut-S beta-lactamase VII testing kit based on liquied microdilution, the readings were obtained by a multı-scan spectrometer, and the data was automatically analyzed by the sıfın a software. All the ESBL screening and confirmatory testings were conducted according to the criteria by Clinical and Laboratory Standarts Institute (2013).The results revealed that the phenotypic screening for ESBL production yielded 40 suspected isolates in Enterobacteriaceae. Of 40 isolates, 29 of them were confirmed as ESBL-producer. The most common phenotype was determined to be E. coli(79.4%), followed byE. cloacae(10.3%), andC.braakii(10.3%), respectively. To conclude, our study indicated that the raw milks were significantly contaminated with ESBL-producing Enterobacteriaceae, potentially leading to a risk to the public health. In the recent years, we strictly advise that the antibiotic agents used for the farming animals should be carefully controlled, and the ESBL-producing enterobacteria should be included in the food regulations as a food safety indicating parameter.