Virulence markers of Shiga-like toxin-producing Escherichia coli strains originating from healthy domestic animals of different species

Abstract

Shiga-like toxin (verotoxin)-producing strains of Escherichia coli (SLTEC) originating from healthy cattle, sheep, goats, pigs, cats, and dogs were investigated for properties which are related to virulence of E. coli for humans. The slt-II (Shiga-like toxin II) and slt-IIc genes were frequent in SLTEC from healthy cattle and dogs but were rarely found in SLTEC from other animals. The slt-IIe gene was detected only in porcine SLTEC. SLTEC from goats and SLTEC from sheep were found to carry different SLT-II determinants which were not further characterized genetically. Sixty (28.8%) of 208 SLTEC from healthy animals showed diffuse adherence to HEp-2 cells. However, none of the strains was positive for genes specific for the local adherence (eaf), diffuse adherence (daa), or enteroaggregative (EAggEC) E. coli type. Only 3 (1.4%) of the 208 SLTEC were positive for attaching and effacing E. coli (eae) sequences. The enterohemolytic phenotype was present in 128 of the 208 SLTEC. Almost all enterohemolytic animal SLTEC were found to carry DNA sequences specific for the plasmid-encoded enterohemorrhagic E. coli hemolysin of E. coli O157. Bacteriophage-associated enterohemolysin (Ehly1 and Ehly2)-specific sequences were detected only in 14.4% of the 208 SLTEC and were linked with certain serotypes. The SLTEC from healthy animals constitute a very heterogeneous group of E. coli, and many of these strains appeared to be specific for their hosts. The absence of eae sequences in most animal SLTEC could indicate that these strains are less virulent for humans than the classical eae-positive enterohemorrhagic E. coli types.