Evaluation of the impact of quorum sensing transcriptional regulator SdiA on long-term persistence and fecal shedding of Escherichia coli O157:H7 in weaned calves

Abstract

Escherichia coli O157:H7 (O157) colonization of bovine intestine is mediated through the locus of enterocyte effacement (LEE)-encoded type III secretion system and secreted virulence proteins that promote colonization of the recto-anal junction (RAJ) of the large intestine of cattle. The quorum sensing transcriptional regulator SdiA, a homolog of LuxR, has been shown in vitro to repress LEE strongly when overexpressed from a multi-copy recombinant plasmid or when its activity is enhanced by the binding of N-acyl-L-homoserine lactones (AHLs), the quorum sensing signals that are detected by SdiA. Since LEE has been shown to be essential for colonization and persistence of O157 in bovine intestine, we examined whether a mutation in sdiA, which normally represses LEE in vitro, would also exert negative effect on colonization and long-term persistence of O157 in weaned calves. Ten-week old weaned calves (n = 4/group) were inoculated orally with 1010 cfu of either the wild-type or sdiA mutant strain. Initial fecal shedding of the sdiA mutant and the wild-type strain were similar in magnitude and declined during the first 2 weeks post-inoculation. The sdiA mutant was detected in feces of only one of the four calves at low levels (≥102 cfu/g feces) from days 19 − 27 post-inoculation, whereas, the fecal shedding of the wild-type strain persisted at approximately 4-logs in all four calves from days 19 − 27. We also confirmed that SdiA represses ler, which encodes a positive transcriptional regulator of LEE, in response to AHLs, and reduces adherence of O157 to HEp-2 cells. In conclusion, this study demonstrates that although in vitro the sdiA gene represses LEE and LEE-mediated adherence to cultured cells, the presence of sdiA is necessary for colonization of bovine large intestine that in turn promotes persistent fecal shedding of O157 by these animals.