Two hundred and eighteen (218) fish samples collected from gills and muscles of Nile tilapia sold in two market regions in El-Behera governorate; Damanhour and Abou-homus, were examined for the presence of E. coli. Forty E. coli isolates (29 from gills and 11 from muscles) were identified by culture, biochemical analysis and PCR. Further, the isolates were studied for their antimicrobial susceptibility patterns using 9 antibiotics commonly used in the veterinary and medical fields. The highest resistances were by E. coli isolates from the gills against ampicillin, streptomycin, sulfamethoxazole-trimethobrim and tetracycline with 97.5%, 65%, 57% and 50%, respectively. While sensitivities were detected to Amikacin (97.5%), Ciprofloxacin (90%), Cefotaxime (67.5%) and Gentamycin (60%). Multiple antibiotic resistances were detected in 95% (38/40) of the isolates. Higher MAR index was detected from E.coli isolates from the gills and 24 different resistance phenotypes were detected. PCR for the detection of the virulence genes; eaeA and stx2 and antimicrobial resistance genes; blaTEM, tetA(A), sul1 and aadA2 was performed. All tested isolates were 100% positive for the blaTEM gene. The eaeA, tetA(A) and Sul1 genes were detected in 83.3% (5/6) of the tested isolates, while the stx2 and aadA2 genes were detected in 50% only. These results collectively indicate that Nile tilapia in market can harbor pathogenic E. coli and act as a reservoir for multi-resistance E. coli and facilitate its transmission and dissemination.
Key words: E.coli, Nile tilapia, antimicrobial resistance, Egypt, STEC