Identification of the anti-terminator qO111:H- gene in Norwegian sorbitol-fermenting Escherichia coli O157:NM

Abstract

Sorbitol-fermenting Escherichia coli O157:NM (SF O157) is an emerging pathogen suggested to be more virulent than nonsorbitol-fermenting Escherichia coli O157:H7 (NSF O157). Important virulence factors are the Shiga toxins (stx), encoded by stx1 and/or stx2 located within prophages integrated in the bacterial genome. The stx genes are expressed from pR′ as a late protein, and anti-terminator activity from the Q protein is necessary for read through of the late terminator tR′ and activation of pR′. We investigated the regulation of stx2EDL933 expression at the genomic level in 17 Norwegian SF O157. Sequencing of three selected SF O157 strains revealed that the anti-terminator q gene and genes upstream of stx2EDL933 were identical or similar to the ones observed in the E. coli O111:H- strain AP010960, but different from the ones observed in the NSF O157 strain EDL933 (AE005174). This suggested divergent stx2EDL933-encoding bacteriophages between NSF O157 and the SF O157 strains (FR874039-41). Furthermore, different DNA structures were detected in the SF O157 strains, suggesting diversity among bacteriophages also within the SF O157 group. Further investigations are needed to elucidate whether the qO111:H- gene observed in all our SF O157 contributes to the increased virulence seen in SF O157 compared to NSF O157. An assay for detecting qO111:H- was developed. © 2012 Federation of European Microbiological Societies.