Evaluating virulence of waterborne and clinical Aeromonas isolates using gene expression and mortality in neonatal mice followed by assessing cell culture's ability to predict virulence based on transcriptional response

Tetrahymena: an alternative model host for evaluating virulence of Aeromonas strains

An easier assessment model would be helpful for high-throughput screening of Aeromonas virulence. The previous study indicated the potential of Tetrahymena as a permissive model to examine virulence of Aeromonas hydrophila. Here our aim was to assess virulence of Aeromonas spp. using two model hosts, a zebrafish assay and Tetrahymena-Aeromonas co-culture, and to examine whether data from the Tetrahymena thermophila model reflects infections in the well-established animal model. First, virulence of 39 Aeromonas strains was assessed by determining the 50% lethal dose (LD(50)) in zebrafish. LD(50) values ranging from 1.3×10(2) to 3.0×10(7) indicated that these strains represent a high to moderate degree of virulence and could be useful to assess virulence in the Tetrahymena model. In Tetrahymena-Aeromonas co-culture, we evaluated the virulence of Aeromonas by detecting relative survival of Aeromonas and Tetrahymena. An Aeromonas isolate was considered virulent when its relative survival was greater than 60%, while the Aeromonas isolate was considered avirulent if its relative survival was below 40%. When relative survival of T. thermophila was lower than 40% after co-culture with an Aeromonas isolate, the bacterial strain was regarded as virulent. In contrast, the strain was classified as avirulent if relative survival of T. thermophila was greater than 50%. Encouragingly, data from the 39 Aeromonas strains showed good correlation in zebrafish and Tetrahymena-Aeromonas co-culture models. The results provide sufficient data to demonstrate that Tetrahymena can be a comparable alternative to zebrafish for determining the virulence of 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.

Aeromonas caviae strain induces Th1 cytokine response in mouse intestinal tract

Aeromonas caviae has been associated with human gastrointestinal disease. Strains of this species typically lack virulence factors (VFs) such as enterotoxins and hemolysins that are produced by other human pathogens of the Aeromonas genus. Microarray profiling of murine small intestinal extracts, 24 h after oral infection with an A. caviae strain, provides evidence of a Th1 type immune response. A large number of gamma-interferon (gamma-IFN) induced genes are up-regulated as well as several tumor necrosis factor-alpha (TNF-alpha) transcripts. Aeromonas caviae has always been considered an opportunistic pathogen because it lacks obvious virulence factors. This current effort suggests that an A. caviae strain can colonize the murine intestinal tract and cause what has been described by others as a dysregulatory cytokine response. This response could explain why a number of diarrheal waterborne disease cases have been attributed to A. caviae even though it lacks obvious enteropathogenic properties.

Predicting virulence of Aeromonas isolates based on changes in transcription of c-jun and c-fos in human tissue culture cells

AIMS

To screen for the virulence potential of Aeromonas isolates based on the change in regulation of c-jun and c-fos in the human intestinal tissue culture cell line Caco-2.

METHODS AND RESULTS

Aeromonas cells were added to Caco-2 cells at a ratio of approx. 1 : 1. After 1-, 2- and 3-h incubation at 37 degrees C, mRNA was extracted from the cells and gene expression of two host genes, c-jun and c-fos, quantified. Aeromonas isolates which were pathogenic in the neonatal mouse model demonstrated up-regulation of c-jun and c-fos compared to avirulent isolates.

CONCLUSIONS

Human cell culture results showed that c-jun and c-fos were predictive of Aeromonas virulence.

SIGNIFICANCE AND IMPACT OF THE STUDY

An Aeromonas relative virulence scale is proposed for use in the testing of Aeromonas drinking water isolates.