Identification and characterization of extended-spectrum β-lactamases (ESBL) producing Escherichia coli isolated from raw milk samples of different dairy farms in Mymensingh, Bangladesh

Adnan Ahmed; Shahed Khan; Himangsu Sarker; A. K. M. Anisur Rahman; Md Mahbub Alam

doi:10.5455/EJMID.20250901014739

Abstract
Background: Milk serves as a conducive medium for pathogenic bacteria, such as Escherichia coli, presenting a significant public health concern due to the rise of antibiotic-resistant strains within the dairy supply chain.
Aim: The objective of this study was to ascertain the prevalence and characteristics of E. coli in raw cow milk from Mymensingh, Bangladesh, identifying antibiotic-resistant and virulent genes, and analysing antibiograms.
Methods: From July 2023 to June 2024, 100 raw milk samples from Mymensingh were examined. E. coli isolates were identified through microbiological and biochemical methods. PCR screening identified specific resistance genes (blaTEM, blaSHV, blaCTX-M) and virulence genes (fimH, stx-1, papC, sfa).
Findings: E. coli was identified in 63% of the samples. Among these, 88.9% exhibited at least one virulence gene, with fimH at 84% being the predominant variant. ESBL-encoding genes were identified in 21 isolates (33.3% of the 63 E. coli isolates), with blaTEM found in 25% of the isolates. Phenotypically ESBL-positive strains exhibited significant resistance to ampicillin at 96% and tetracycline at 67%. All isolates exhibited sensitivity to meropenem. Multidrug-resistant (MDR) isolates were detected.
Conclusion: The simultaneous occurrence of antibiotic-resistant and virulent E. coli underscores a considerable food safety hazard. Given that this study limited to a single district, the findings of stx-1 indicates a possible threat of contamination by Shiga toxin-producing E. coli (STEC), which may result in serious illness. Integrated One Health surveillance and sophisticated techniques such as whole-genome sequencing and MLST are essential for monitoring strain diversity and safeguarding public health.

Key words: Escherichia coli; Milk; PCR; Resistance genes; Virulence genes