Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2013
Publication Date: 2/13/2013
Citation: Sharma, V.K., Bearson, S.M. 2013. 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. Microbial Pathogenesis. 57:21-26.
Interpretive Summary: Escherichia coli O157:H7 (E. coli O157:H7) are Shiga toxin-producing bacteria that infect humans through the consumption of contaminated meats, unpasteurized dairy products, fresh produce and water. Infections in humans with these bacteria produce disease symptoms ranging from watery to bloody diarrhea that in young children and elderly individuals could lead to kidney malfunction and even death. Cattle are the major reservoir for O157. O157 bacteria can colonize and persist in the intestines of cattle without causing disease, but colonized animals can shed O157 in their feces at variable magnitudes and for extended periods of time. Cattle feces are the major risk factor for the contamination of animal hides in feedlots and carcass contamination at slaughter plants leading to the downstream contamination of meat products. Cattle manure is also a major risk factor for the contamination of water resources and environmental spread of O157. According to CDC estimates, O157 causes over 73000 human illnesses per year in the U.S.A with over 2000 cases of hospitalizations and 61 deaths. Combined economic losses due to human illnesses and food contamination are estimated at almost a billion dollars. Thus, a concerted approach is needed to identify bacterial factors that promote O157 colonization of cattle intestines leading to long-term persistence and fecal shedding of these bacteria by these animals. Bacterial factors identified through the successful execution of these studies could then be tested as potential targets for incorporation into novel vaccines for reducing colonization and persistence of O157 in these animals. In addition, these bacterial targets could potentially be tested in screening procedures designed to identify inhibitors (biological or chemical) of O157 growth by blocking the function of these targets. Thus, combinations of vaccines and biological inhibitors could provide highly effective remedies for reducing colonization and fecal shedding of O157 in cattle, thus reducing the risks of downstream contamination of meats, produce, and water.
Technical Abstract: Quorum sensing transcriptional regulator SdiA has been shown to enhance the survival of Escherichia coli O157:H7 (O157) in the acidic compartment of bovine rumen in response to N-acyl-L-homoserine lactones (AHLs) produced by the rumen bacteria. Bacteria that survive the rumen environment subsequently colonize recto-anal junction (RAJ) of the large intestine. The RAJ colonization is mediated through LEE, which encodes for a type III secretion system and secreted virulence proteins. In the current study, we used 10-week old weaned calves to infer the role of sdiA in survival of O157 in rumen and in subsequent colonization of the large intestine. Calves (n = 4 for each strain) were inoculated orally with 10**10 cfu of either the wild-type strain or sdiA mutant. Fecal shedding of the mutant and wild-type strain declined rapidly and by similar magnitudes for the first 2 weeks post-inoculation. While the sdiA mutant was detected in feces of one of four calves at very low levels (greater than or equal to 10**2 cfu/g feces) from days 19 - 27 (p less than 0.001), fecal shedding of the wild-type strain increased to and persisted at 4-logs in all four calves from days 19 - 27. We also demonstrated that SdiA represses LEE in response to AHLs and reduction in adherence of O157 to HEp-2 cells is correlated with the level of SdiA expression. In conclusion, monitoring of fecal shedding for 4 weeks in younger animals provided unequivocal evidence that SdiA enhanced survival of O157 in the rumen is a prerequisite for colonization of the large intestine.