The widespread occurrence of the enterohemolysin gene ehly among environmental strains of Escherichia coli
Abstract (Summary)The goals of this research project were to determine the prevalence of the virulence factor enterohemolysin, encoded by the ehly gene, in environmental samples of Escherchia coli and to determine if molecular probing for this virulence factor could serve as a useful indicator of enterohemorrhagic E. coli (EHEC). Molecular probing for the enterohemolysin gene was further tested in this project by using it to screen for EHEC in environmental samples. E. coli O157:H7 has been linked to waterborne outbreaks in the United States and abroad (Picard et al., 1999; Vaz et al., 2004; Vernozy-Rozand et al., 2002). Methods currently employed to detect this pathogen are cultural based and take advantage of phenotypic traits that are specific for this serotype, including slow sorbitol fermentation and negative ?-glucuronidase activity. The main concern with using these techniques is that the other EHEC strains, implicated in human illness, do not exhibit the same phenotypic characteristics as strain E. coli O157:H7. As a consequence many potential strains of EHEC other than O157:H7 are not easily detected. An EHEC is classified by the organism’s ability to produce specific virulence factors (VF). All of these VF must be present for the organism to be classified as EHEC. The VF required are: enterohemolysin, intimin, and one or more Shiga-like toxins (SXTI, SXTII). Molecular probing for one or more of these virulence factors could be a powerful tool for examining waterborne EHEC outbreaks. This study focused on one of the VF produced by EHEC, enterohemolysin production, as a way of isolating EHEC from wastewater effluents in the US. The results presented in this study demonstrate that domestic sewage in the US is not a significant source of EHEC. Seven municipal wastewater treatment plant effluents were surveyed from geographically distinct areas across the United States. The effluents were screened for E. coli exhibiting the classical EHEC hemolysis on enterohemolysin blood agar. A total of 338 enterohemolysin positive E. coli isolates were recovered from the wastewater effluents. The isolates were further analyzed, using the polymerase chain reaction and specific primers, for the presence of additional VF: SXTI, SXTII, and intimin. Only two of the 338 isolates possessed a VF in addition to enterohemolysin production. These two strains tested positive for the presence of the VF intimin. It was determined by this study that the VF enterohemolysin is common among environmental E. coli, however since none of the isolated strains had the additional VF they are not considered to be EHEC. Therefore the results from this study suggest that probing for the enterohemolysin VF alone may not be a good indicator of EHEC.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2005