High prevalence of CTX-M-1 and CTX-M-15 extended-spectrum β-lactamase-producing Escherichia coli in retail imported frozen beef in Saudi Arabia

Background and Aim: The global expansion of antimicrobial resistance (AMR), particularly due to extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, represents a critical threat to food safety and public health. Imported meat products are increasingly recognized as potential vehicles for the transboundary dissemination of multidrug-resistant (MDR) bacteria. However, data on the occurrence and molecular characteristics of ESBL-producing E. coli in imported frozen beef in Saudi Arabia remain limited. This study aimed to determine the prevalence, AMR profiles, and ESBL gene distribution among E. coli isolated from retail imported frozen beef. Materials and Methods: A total of 78 imported frozen boneless beef samples were collected from retail shops and supermarkets in Dammam and Al Khobar, Eastern Province, Saudi Arabia. E. coli isolation was performed using Enterobacteriaceae enrichment broth followed by CHROMagar™ E. coli. Presumptive isolates were screened on CHROMagar™ ESBL and subjected to antimicrobial susceptibility testing against 21 antimicrobials using the disc diffusion method. Phenotypic confirmation of ESBL production was conducted using E-test ESBL strips. Molecular detection of ESBL-encoding genes (blaTEM, blaSHV, blaCTX-M-1, blaCTX-M-9, and blaCTX-M-15) was performed by polymerase chain reaction. Results: From 78 beef samples, 390 E. coli isolates were recovered, of which 361 (92.5%) were presumptive ESBL producers on CHROMagar™ ESBL. Phenotypic confirmation showed that 319/361 (88.3%) isolates were ESBL-producing E. coli. Molecular analysis detected β-lactamase genes in 324/361 (89.7%) isolates, with blaCTX-M-1 and blaCTX-M-15 each identified in 87.5% of isolates. High resistance rates were observed to ampicillin (99.4%), cephalothin (97.2%), cephalexin (91.4%), ceftriaxone (81.9%), and cefotaxime (73.9%). MDR was detected in 97.2% of isolates. Conclusion: Retail imported frozen beef in Saudi Arabia harbors an exceptionally high burden of MDR ESBL-producing E. coli, predominantly driven by CTX-M-1 and CTX-M-15 enzymes. These findings indicate that international beef supply chains may act as significant reservoirs for high-risk ESBL determinants, underscoring the need for strengthened surveillance, regulatory control, and One Health-based interventions to limit foodborne dissemination of AMR. Keywords: antimicrobial resistance, beef safety, Escherichia coli, extended-spectrum beta-lactamase, foodborne pathogens, imported meat, multidrug resistance, One Health.