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

## TL;DR

This study found a high rate of antibiotic-resistant E. coli in retail meat, especially in chicken, raising concerns about public health and the need for better monitoring.

## Contribution

The study reports the co-occurrence of ESBL and colistin resistance genes in E. coli from retail meat in Türkiye, with rare mcr-1/mcr-2 co-carriage in lamb.

## Key findings

- ESBL-producing E. coli were found in 21.7% of meat samples, with the highest prevalence in chicken parts and giblets.
- Six isolates were colistin-resistant, all carrying the mcr-1 gene, and one lamb isolate carried mcr-2.
- The most common resistance gene combination was blaCTX-M1 + blaTEM, mainly in chicken samples.

## Abstract

Background: The emergence of extended-spectrum β-lactamase (ESBL) producing and colistin-resistant Escherichia coli in retail meat poses a significant public health risk. Method: 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 uspA PCR, and resistance genes (blaCTX-M, blaTEM, blaOXA, blaSHV, mcr-1, mcr-2, mcr-3) were analyzed. Colistin MICs were determined by broth microdilution, while antimicrobial susceptibility of ESBL-positive isolates was assessed by disk diffusion. Results: Overall, ESBL-producing E. coli were detected in 21.7% (n = 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-E. coli isolates harbored blaCTX-M, with blaCTX-M-1 identified as the sole variant. The blaTEM gene was detected in 61.5% (24/39) of ESBL-positive E. coli isolates. Colistin resistance was identified in six isolates (15.4%), all of which carried the mcr-1 gene. Additionally, one lamb minced meat isolate harbored the mcr-2 gene. Co-occurrence analysis revealed that the most frequent resistance gene combination among ESBL-producing isolates was blaCTX-M1 + blaTEM, detected predominantly in chicken meat samples, while mcr-1 was observed only in isolates harboring single or limited resistance genes, suggesting a distinct acquisition pattern. Conclusions: A high prevalence of blaCTX-M-1 and the co-occurrence of mcr genes were detected in E. coli isolates from retail meat, particularly poultry. The detection of mcr-1/mcr-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.