Sorbitol-fermenting (SF) Escherichia coli O157:H- strains have emerged as important pathogens and have been
associated with a higher incidence of progression to hemolytic–uremic syndrome (HUS) than non-sorbitol
fermenting (NSF) E. coli O157:H7. The present study was carried out to determine the prevalence of SF E. coli
O157:H- and NSF E. coli O157:H7 strains in retail beef products in Mansoura, Egypt. The contamination rates
with rfbEO157-positive E. coli O157 strains were 26.7% (8/30), 10% (3/30) and 3.7% (1/27) in ground beef, beef
burger, and fresh beef samples, respectively with an overall mean of 13.8% (12/87) among all meat products
tested. SF E. coli O157:H- were the most dominant among the isolated O157 strains. Of the fifteen O157 strains
isolated, 11 (73.3%) were SF E. coli O157:H-, while the remaining 4 (26.7%) were NSF E. coli O157:H7. The 11 SF
O157H- strains were genetically positive for sfpA gene. Restriction fragment length polymorphism (RFLP)
analysis for fliC gene demonstrated a similar pattern for both SF and NSF O157 isolates. PCR assays verified
the existence of stx1 gene in 7 (46.7%) and stx2 gene in 13 (86.7%) of the 15 O157 strains isolated. Unexpectedly,
two of the 15 O157 strains isolated were negative for Shiga toxin genes. The eae gene was identified in all of the
15 O157 strains except in one NSF O157:H7 strain. EHEC-hlyA gene was detected in 14 (93.3%) of the 15 O157
isolates, nonetheless only 11 strains showed enterohemolytic phenotype on blood agar. A combination of the
four virulence genes, stx1, stx2, eae and EHEC-hlyA were detected in 7 (46.7%) strains, while six (40%) strains
were positive for stx2, eae and hlyA genes. This is the first record for isolation of E. coli O157: H- in Egypt as
well as in the African continent. |
