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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR MECHANISMS OF PATHOGENIC BACTERIA INTERACTIONS WITH PLANT SURFACES AND ENVIRONMENTAL MATRICES

Location: Environmental Microbial and Food Safety Laboratory

Title: Hypervirulent- host-associated Citrobacter rodentium cells have poor acid tolerance

Authors
item Smith, Allen
item Bhagwat, Arvind

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2012
Publication Date: May 1, 2013
Citation: Smith, A.D., Bhagwat, A.A. 2013. Hypervirulent- host-associated Citrobacter rodentium cells have poor acid tolerance. Current Microbiology. 66(5):522-526.

Interpretive Summary: In recent food-borne diarrheal outbreaks, strains with enhanced virulence and infectivity have been isolated. Such transient increase in the disease causing potential of food-borne pathogens presents a formidable challenge for epidemiological investigations. Citrobacter rodentium is a mouse pathogen that mimics many aspects of enterohemorrhagic E. coli O157:H7 infection of humans and serves as a useful model for studying virulence mechanisms. In this study,- C. rodentium developed a hyperinfectious state (i.e., fewer bacteria required for illness)once it was passed through the mouse gastrointestinal tract. It is routinely assumed that the hyperinfectious state is, at least in part, due to decreased acid sensitivity. However, the hyperinfectious C. rodentium cells were extremely acid sensitive compared to cells grown in laboratory media. Growth under anaerobic conditions or on fecal components were also not responsible for the hyperinfectious state. Developing tools to identify traits of hyper-virulent outbreak strains is critical to better understanding the food safety risk. This information will be useful to other scientists, the food industry and to regulatory agencies.

Technical Abstract: Enhanced virulence or infectivity after passage through a mammalian host has been reported for a number of enteric food-borne pathogens. Citrobacter rodentium is a mouse pathogen that mimics many aspects of enterohemorrhagic E. coli infection of humans and serves as a useful model for studying virulence mechanisms. Emergence of a hyperinfectious state after passage through mouse gastrointestinal tract was reported for C. rodentium. Acid tolerance of enteric food-borne pathogens is considered an important trait which enables pathogens survive stomach acidity during their passage to gastrointestinal tract to cause disease. We wanted to investigate if increased acid tolerance could explain hypervirulence status of C. rodentium. Although we were able to observe hyperinfectious state of C. rodentium due to host passage, the cells were extremely acid sensitive compared to cells grown in laboratory media. Growth under mildly acidic conditions (LB-MES, pH 5.5) although induced acid tolerance of C. rodentium did not improve organism’s ability to establish infection. Growth under anaerobic environment or on fecal components also did not induce hyperinfectious state. Developing tools to identify traits of hyper-virulent outbreak strains would provide better measure of causality and food safety risk.

Last Modified: 8/27/2014
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