Combating colistin- and cefotaxime-resistant Shiga toxin-producing Escherichia coli in dairy-based products: Occurrence, characterization, and ε-poly-L-lysine growth inactivation.

Abstract

Continuous monitoring of foodborne pathogens, especially multidrug-resistant (MDR) bacteria, is crucial for the food industry, healthcare, and regulatory agencies. This study assessed the prevalence, antimicrobial resistance, and virulence genes (stx1, stx2, and eaeA) in Escherichia coli strains isolated from milk and dairy-based products. In addition, the inhibitory activity of ε-poly-L-lysine (ε-PL) against E. coli O26:H11in vitro and in vivo (ice cream and cheese) was evaluated for the first time. A total of 300 samples, including market raw milk, pasteurized milk, Kariesh cheese, Damietta cheese, ice cream, and yoghurt (50 samples of each product), were analyzed. The results revealed that Kariesh cheese had the highest E. coli prevalence rate at 28%, followed by ice cream, market raw milk, and Damietta cheese at 24%, 22%, and 14%, respectively. The serological identification revealed that the isolates (n=88) belonged to 4 different pathotypes. Surprisingly, more than 80% of isolates showed resistance against tetracycline, gentamicin, and ampicillin. In addition, 36.36% and 21.59% of the isolates were resistant to cefotaxime and colistin, respectively. The molecular characterization revealed that 67, 41, and 2 isolates harbored stx2, stx1, and eaeA genes, respectively. Treatment of artificially contaminated Damietta cheese and vanilla ice cream with ε-PL at a minimum inhibitory concentration (MIC) of 0.1 mg/mL resulted in a notable reduction (p < 0.05) against cefotaxime and colistin-resistant Escherichia coli O26:H11. Therefore, ε-PL can be considered a promising eco-friendly food preservative with a potent antimicrobial activity against multi-drug-resistant bacteria in the food industries.