Open Access Highly Accessed Research article

In vivo bioluminescence imaging of Escherichia coli O104:H4 and role of aerobactin during colonization of a mouse model of infection

Alfredo G Torres12*, Roberto J Cieza1, Maricarmen Rojas-Lopez1, Carla A Blumentritt1, Cristiane S Souza13, R Katie Johnston1, Nancy Strockbine4, James B Kaper5, Elena Sbrana1 and Vsevolod L Popov2

Author Affiliations

1 Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX, 77555-1070, USA

2 Department of Pathology, Sealy Center for Vaccine Development, University of Texas Medical Branch, Galveston, TX, 77555-1070, USA

3 Bacteriology Laboratory, Instituto Butantan, São Paulo, 05503-900, Brazil

4 Enteric Diseases Laboratory Branch, Centers for Disease Control and Prevention, Atlanta, GA, 30333, USA

5 Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA

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BMC Microbiology 2012, 12:112  doi:10.1186/1471-2180-12-112

Published: 20 June 2012

Abstract

Background

A major outbreak of bloody diarrhea associated with Shiga toxin-producing Escherichia coli O104:H4 occurred early in 2011, to which an unusual number of hemolytic uremic syndrome cases were linked. Due to limited information regarding pathogenesis and/or virulence properties of this particular serotype, we investigated the contribution of the aerobactin iron transport system during in vitro and in vivo conditions.

Results

A bioluminescent reporter construct was used to perform real-time monitoring of E. coli O104:H4 in a mouse model of infection. We verified that our reporter strain maintained characteristics and growth kinetics that were similar to those of the wild-type E. coli strain. We found that the intestinal cecum of ICR (CD-1) mice was colonized by O104:H4, with bacteria persisting for up to 7 days after intragastric inoculation. MALDI-TOF analysis of heat-extracted proteins was performed to identify putative surface-exposed virulence determinants. A protein with a high similarity to the aerobactin iron receptor was identified and further demonstrated to be up-regulated in E. coli O104:H4 when grown on MacConkey agar or during iron-depleted conditions. Because the aerobactin iron acquisition system is a key virulence factor in Enterobacteriaceae, an isogenic aerobactin receptor (iutA) mutant was created and its intestinal fitness assessed in the murine model. We demonstrated that the aerobactin mutant was out-competed by the wild-type E. coli O104:H4 during in vivo competition experiments, and the mutant was unable to persist in the cecum.

Conclusion

Our findings demonstrate that bioluminescent imaging is a useful tool to monitor E. coli O104:H4 colonization properties, and the murine model can become a rapid way to evaluate bacterial factors associated with fitness and/or colonization during E. coli O104:H4 infections.