Molecular analysis of multidrug resistance in Shiga toxin-producing Escherichia coli O157:H7 isolated from meat and dairy products

• This study highlights high incidence of multidrug-resistant STEC O157:H7.
• Class 1 and class 2 integrons were identified in meat and dairy products.
• β-Lactamase-encoding genes were identified in 63.0% of MDR O157:H7 isolates.
• Plasmid-mediated quinolone resistance genes were identified, for the first time, in STEC O157:H7.
• Florfenicol resistance gene, floR, was identified, for the first time, in STEC O157:H7.

Shiga toxin-producing Escherichia coli (STEC) O157:H7 is an important food-borne pathogen that has been implicated in numerous disease outbreaks worldwide. Little is known about the extent and molecular basis of antimicrobial resistance in STEC O157:H7 of food origin. Therefore, the current study aimed to characterize the genetic basis of multidrug resistance in 54 STEC O157:H7 strains isolated from 1600 food samples (800 meat products and 800 dairy products) collected from different street venders, butchers, retail markets, and slaughterhouses in Egypt. Thirty-one of 54 (57.4%) isolates showed multidrug resistance phenotypes to at least three classes of antimicrobials. The highest incidence of antimicrobial resistance was to kanamycin (96.8%), followed by spectinomycin (93.6%), ampicillin (90.3%), streptomycin (87.1%), and tetracycline (80.6%). PCR and DNA sequencing were used to screen and characterize integrons and antibiotic resistance genes, and 29.6% and 5.6% of isolates were positive for class 1 and class 2 integrons, respectively. β-Lactamase-encoding genes were identified in 63.0% of isolates as follows: blaTEM-1 and blaTEM-52 in 35.2% and 1.9% isolates respectively; blaCMY-2 in 13.0% isolates; blaCTX-M in 5.6% isolates; blaSHV-12 in 5.6% isolates; and blaOXA-1 in 1.9% isolate. The plasmid-mediated quinolone resistance genes were identified in 13.0% of isolates as follows: qnrB, qnrS, and aac(6′)-Ib-cr in 5.6%, 3.7%, and 3.7% isolates, respectively. Finally, the florfenicol resistance gene floR was identified in 7.4% of isolates. This study demonstrated that meat and dairy products are potential sources of multidrug resistant STEC O157:H7. To our knowledge, this is the first report of the occurrence of class 2 integrons, qnrB, qnrS, and aac(6′)-Ib-cr in STEC O157:H7.