Adhesion and cytotoxicity of Aeromonas caviae to rabbit intestinal epithelium ex vivo.

UNLABELLED: Aeromonads are considered potential pathogens for humans and animals and are responsible for the etiology of intestinal and extraintestinal diseases. The presence of Aeromonas spp. in food and water shows that it is an important vehicle of infection in humans. The pathology caused by these bacteria involves several virulence factors, such as the ability to produce toxins, adhesion and invasion. The present study investigated the interaction of five Aeromonas caviae strains isolated from human diarrheic faeces with rabbit ileal and colonic mucosa ex vivo, using in vitro organ culture model. The in vitro adhesion assays using cultured tissue were performed with A. caviae strains co-incubated with intestinal fragments of ileum and colon over a period of 6 h. The fragments were analyzed by light and electron microscopy. All strains adhered to rabbit ileal and colonic mucosa ex vivo, with higher degree of adherence presented on colonic mucosa. The typical aggregative adherence pattern was observed among strains studied. Through electron and light microscopy, we observed extensive colonization of ileal and colonic mucosa, large mucus production, biofilm formation and morphological alterations such as intense vacuolization, structural disorganization, cell extrusion and destruction of the villi. These results demonstrate that in vitro organ culture of intestinal mucosa from rabbit may be used to investigate Aeromonas spp. PATHOGENESIS: Finally, our results support the pathogenic potential of Aeromonas emphasising their importance in public health.

Adhesion, invasion, intracellular survival and cytotoxic activity of strains of Aeromonas spp. in HEp-2, Caco-2 and T-84 cell lines.

The genus Aeromonas contains important pathogen for both humans and other animals, being responsible for the etiology of intestinal and extraintestinal diseases. The pathology caused by these bacteria involves several virulence factors, such as the ability to produce toxins, adhesion and invasion. The properties conferred by these factors have been extensively studied in experiments of interaction between bacterial strains and cell culture. We evaluate the interaction of eight Aeromonas spp. strains, previously isolated from human faeces, food and water with HEp-2, Caco-2 and T-84 cell lines. Cytotoxic effects, the pattern of adhesion, invasive capacity and intracellular survival were analyzed. The results showed that Aeromonas strains were adherent to three cells lines in 6 h of incubation, displaying the aggregative adherence pattern. Among eight strains studied, 50% produced cytotoxic effects on HEp-2 cells, while none of the strains produced cytotoxic effects on Caco-2 and T-84 cells at 48 h. This study demonstrated that subsets of Aeromonas isolated from different sources were able to invade intestinal (T-84, Caco-2) and epithelial (HEp-2) cell lines cultivated in vitro surviving in intracellular environments up to 72 h. Finally, our results support the pathogenic potential of Aeromonas, especially those of food and clinical sources.

Genotypic and phenotypic characterisation of enteroaggregative Escherichia coli from children in Rio de Janeiro, Brazil.

Enteroaggregative Escherichia coli (EAEC) is a significant cause of diarrhoeal illness in both children and adults. Genetic heterogeneity and recovery of EAEC strains from both healthy and diseased individuals complicates our understanding of EAEC pathogenesis. We wished to establish if genetic or phenotypic attributes could be used to distinguish between strains asymptomatically colonising healthy individuals and those which cause disease. Genotypic screening of a collection of twenty four EAEC isolates from children with and without diarrhoea revealed no significant differences in the repertoire of putative virulence factors present in either group of strains. In contrast, EAEC strains from phylogroup A were more strongly associated with asymptomatic groups whereas strains from phylogroup D were more associated with cases of diarrhoea. Phenotypic screening revealed no differences in the ability of strains from either cohort of children to form biofilms, to adhere to and invade cells in tissue culture or to cause disease in the Caenorhabditis elegans model of infection. However, the latter assay did reveal significant reduction in nematode killing rates when specific virulence factors were deleted from human pathogenic strains. Our results suggest that current models of infection are not useful for distinguishing avirulent from pathogenic strains of EAEC but can be useful in studying the effect of specific virulence factors.