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


CONCLUSIONS
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.
Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555-1070, USA. altorres@utmb.edu
Alfredo G
AG
Torres
Roberto J
RJ
Cieza
Maricarmen
M
Rojas-Lopez
Carla A
CA
Blumentritt
Cristiane S
CS
Souza
R Katie
RK
Johnston
Nancy
N
Strockbine
James B
JB
Kaper
Elena
E
Sbrana
Vsevolod L
VL
Popov
D000818:Animals; D002432:Cecum / Q000382:microbiology; D004195:Disease Models, Animal; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology* / Q000473:pathology*; D005260:Female; D017353:Gene Deletion; D006877:Hydroxamic Acids / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D051379:Mice; D008813:Mice, Inbred ICR; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*; D051598:Whole Body Imaging / Q000379:methods
D006877:Hydroxamic Acids; D037521:Virulence Factors; C031819:aerobactin; D007501:Iron