A mouse model for characterization of gastrointestinal colonization rates among environmental Aeromonas isolates

Gastrointestinal colonization rates for human clinical isolates of Aeromonas veronii using a mouse model

A variety of environment-associated gastrointestinal infections have been associated with the Aeromonas group of bacteria which contain both non-virulent strains as well as virulent strains within a particular species. This study monitors the colonization rates of colon tissue in a mouse-streptomycin dose/response model involving isolates of Aeromonas veronii biovar sobria obtained from human clinical specimens. The ability to successfully colonize mouse colon tissues by the human clinical isolates was then compared with the rates achieved in a previous study of Aeromonas isolates obtained from environmental drinking water samples. Results suggest that strains of Aeromonas isolated from drinking water environmental samples contain pathogenic and virulence capabilities similar to those seen in Aeromonas veronii clinical isolates from human infections.

Enterohemorrhagic E. coli alters murine intestinal epithelial tight junction protein expression and barrier function in a Shiga toxin independent manner

Shiga toxin (Stx) is implicated in the development of hemorrhagic colitis and hemolytic-uremic syndrome, but early symptoms of enterohemorrhagic Escherichia coli (EHEC) infection such as nonbloody diarrhea may be Stx independent. In this study, we defined the effects of EHEC, in the absence of Stx, on the intestinal epithelium using a murine model. EHEC colonization of intestines from two groups of antibiotic-free and streptomycin-treated C57Bl/6J mice were characterized and compared. EHEC colonized the cecum and colon more efficiently than the ileum in both groups; however, greater amounts of tissue-associated EHEC were detected in streptomycin-pretreated mice. Imaging of intestinal tissues of mice infected with bioluminescent EHEC further confirmed tight association of the bacteria with the cecum and colon. Greater numbers of EHEC were also cultured from stool samples obtained from streptomycin-pretreated mice, as compared with those that received no antibiotics. Transmission electron microscopy shows that EHEC infection leads to microvillous effacement of mouse colonocytes. Hematoxylin and eosin staining of the colonic tissues of infected mice revealed a slight increase in the number of lamina propria polymorphonuclear leukocytes. Transmucosal electrical resistance, a measure of epithelial barrier function, was reduced in the colonic tissues of infected animals. Increased mucosal permeability to 4- kDa FITC-dextran was also observed in the colonic tissues of infected mice. Immunofluorescence microscopy showed that EHEC infection resulted in redistribution of the tight junction (TJ) proteins occludin and claudin-3 and increased the expression of claudin-2, whereas ZO-1 localization remained unaltered. Quantitative real-time PCR showed that EHEC altered mRNA transcription of OCLN, CLDN2, and CLDN3. Most notably, claudin-2 expression was significantly increased and correlated with increased intestinal permeability. Our data indicate that C57Bl/6J mice serve as an in vivo model to study the physiological effects of EHEC infection on the intestinal epithelium and suggest that altered transcription of TJ proteins has a role in the increase in intestinal permeability.

Different clinical characteristics between polymicrobial and monomicrobial Aeromonas bacteremia--a study of 216 cases

BACKGROUND

Part of Aeromonas bacteremia is polymicrobial infection. However, a clinical comparison of monomicrobial and polymicrobial Aeromonas bacteremia has not hitherto been reported.

METHODS

A retrospective analysis of medical records of patients with Aeromonas bacteremia at three large referral hospitals in Taiwan for an 8-year period (2001-2008) was conducted.

RESULTS

There were 154 patients with monomicrobial Aeromonas bacteremia and 62 patients with polymicrobial Aeromonas bacteremia. In the polymicrobial infections, E. coli was the most common combined pathogen (42%), followed by Klebsiella spp. (24%) and Enterobacter spp. (16%). Multivariate logistic regression analysis revealed solid cancer as the risk factor for polymicrobial Aeromonas bacteremia, with male gender and cirrhosis as risk factors for monomicrobial Aeromonas bacteremia. However, of all types of solid cancer, hepatoma was associated with monomicrobial Aeromonas bacteremia. APACHE II score was the most important prognostic factor in both groups.

CONCLUSION

Aeromonas bacteremia in patients with cirrhosis or male gender tended to be monomicrobial. Polymicrobial Aeromonas bacteremia was associated with solid cancers. In either polymicrobial or monomicrobial Aeromonas bacteremia, prognosis could be predicted according to disease severity measured by APACHE II score.