Molecular characterization and antibiotic resistance of enterotoxigenic and entero-aggregative Escherichia coli isolated from raw milk and unpasteurized cheeses

The aim of this study was to determine the occurrence of enterotoxigenic and enteroaggregative Escherichia coli strains and antibiotic resistance of the isolates in raw milk and unpasteurized cheese. Out of ۲۰۰ samples of raw milk and ۵۰ samples of unpasteurized cheeses, ۹۶ and ۲۴ strains of E. coli were isolated, respectively. Polymerase chain reaction (PCR) was used to detect the genes encoding heat-stable enterotoxin a (STa), heat-stable enterotoxin b (STb), heat labile toxin (LT) and enteroaggregative heat-stable toxin۱ (EAST۱). Twelve out of ۱۲۰ (۱۰.۰۰%) isolates harbored the gene for EAST۱, ۲(۱.۶۶%) isolates were detected as producing STb and LT  toxins and ۱۲ (۱۰.۰۰%) strains contained STb and EAST۱ genes.  None of the strains contain the STa gene. All of the strains were tested for antibiotic resistance by disk diffusion method. Disks included: ciprofloxacin (CFN), trimetoprim-sulfamethoxazole (TSX), oxytetracycline (OTC), gentamicin (GMN), cephalexin (CPN), nalidixic acid (NDA) and nitrofurantoin (NFN), ampicillin (AMP), neomycin (NEO) and streptomycin (STM).  Among ۱۲۰ isolated strains of E. coli, the resistance to each antibiotics were as follows: OTC۱۰۰%, CPN ۸۶.۰۰%, NDA ۵۶.۰۰%, NFN ۴۲.۰۰%, GMN ۳۰.۰۰%, TSX ۲۸.۰۰%, CFN ۲۰%, AM ۲۳.۴۰% and STM ۴.۲۵%. None of the isolates were resistant to NEO. The present data indicate that different resistant E. coli pathogens may be found in raw milk and unpasteurized cheese. It poses an infection risk for human and transferring the resistant factors to microflora of the consumers gut.

کلیدواژه ها:

Antibiotic resistance ، Raw Milk ، Toxigenic E. coli ، Unpasteurized cheese