1887

Abstract

Quorum-sensing (QS) signalling pathways are important regulatory networks for controlling the expression of genes promoting adherence of enterohaemorrhagic (EHEC) O157 : H7 to epithelial cells. A recent study has shown that EHEC O157 : H7 encodes a homologue, called , which upon overexpression reduces the expression of genes encoding flagellar and locus of enterocyte effacement (LEE) proteins, thus negatively impacting on the motility and intimate adherence phenotypes, respectively. Here, we show that the deletion of from EHEC O157 : H7 strain 86-24, and from a (a negative regulator of ) mutant of this strain, enhanced bacterial adherence to HEp-2 epithelial cells of the mutant strains relative to the strains containing a wild-type copy of . Quantitative reverse transcription PCR showed that the expression of LEE-encoded genes , and in strains with the deletions was not significantly different from that of the strains wild-type for . Similarly, no additional increases in the expression of LEE genes were observed in a double mutant strain relative to that observed in the deletion mutant. While the expression of , which encodes flagellin, was enhanced in the mutant strain, the expression of was reduced by several fold in the mutant strain, irrespective of the presence or absence of , indicating that the genes and exert opposing effects on the expression of . The strains with deletions in or showed enhanced expression of , encoding curlin of the curli fimbriae, with the expression of highest in the double mutant, suggesting an additive effect of these two gene deletions on the expression of . No significant differences were observed in the expression of the genes and of the operons encoding long polar and type 1 fimbriae in the mutant strain. These data indicate that SdiA has no significant effect on the expression of LEE genes, but that it appears to act as a strong repressor of genes encoding flagella and curli fimbriae, and the alleviation of the SdiA-mediated repression of these genes in an EHEC O157 : H7 mutant strain contributes to enhanced bacterial motility and increased adherence to HEp-2 epithelial cells.

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2010-05-01
2019-08-24
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