Co-Occurrence and Molecular Characterization of ESBL-Producing and Colistin-Resistant Escherichia coli Isolates from Retail Raw Meat

<b>Background:</b> The emergence of extended-spectrum β-lactamase (ESBL) producing and colistin-resistant <i>Escherichia coli</i> in retail meat poses a significant public health risk. <b>Method:</b> A total of 180 retail meat samples (chicken parts, internals, processed products; lamb; beef; fish) were purchased from markets and butcher shops across Turkiye. Presumptive ESBL-producing isolates were screened on chromogenic agar and phenotypically confirmed. Species identity was verified by <i>uspA</i> PCR, and resistance genes (<i>blaCTX-M</i>, <i>blaTEM</i>, <i>blaOXA</i>, <i>blaSHV</i>, <i>mcr</i>-1, <i>mcr</i>-2, <i>mcr</i>-3) were analyzed. Colistin MICs were determined by broth microdilution, while antimicrobial susceptibility of ESBL-positive isolates was assessed by disk diffusion. <b>Results:</b> Overall, ESBL-producing <i>E. coli</i> were detected in 21.7% (<i>n</i> = 39) of the 180 meat samples analyzed, with the highest prevalence observed in chicken parts (26/40, 65.0%) and giblets (6/10, 60%). All ESBL-<i>E. coli</i> isolates harbored <i>blaCTX-M</i>, with <i>blaCTX-M-</i>1 identified as the sole variant. The <i>blaTEM</i> gene was detected in 61.5% (24/39) of ESBL-positive <i>E. coli</i> isolates. Colistin resistance was identified in six isolates (15.4%), all of which carried <i>the mcr-1 gene</i>. Additionally, one lamb minced meat isolate harbored <i>the mcr-2 gene</i>. Co-occurrence analysis revealed that the most frequent resistance gene combination among ESBL-producing isolates was <i>blaCTX-M1</i> + <i>blaTEM</i>, detected predominantly in chicken meat samples, while <i>mcr</i>-1 was observed only in isolates harboring single or limited resistance genes, suggesting a distinct acquisition pattern. <b>Conclusions:</b> A high prevalence of <i>blaCTX-M</i>-1 and the co-occurrence of <i>mcr</i> genes were detected in <i>E. coli</i> isolates from retail meat, particularly poultry. The detection of <i>mcr</i>-1/<i>mcr</i>-2 co-carriage in lamb meat, though rare, highlights the need for broader surveillance. These findings underscore the need for integrated monitoring and prudent antimicrobial use in food animals. The use of antibiotics as growth promoters is prohibited in Türkiye, and therapeutic applications require a veterinary prescription; however, stronger enforcement remains essential to limit the dissemination of multidrug-resistant bacteria in the food chain.