Aeromonas caviae is a Gram-negative, motile and rod-shaped facultative anaerobe that is increasingly being recognized as a cause of diarrhea in children. Here we present the first genome sequence of an A. caviae strain that was isolated as the sole pathogen from a child with profuse diarrhea.

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.

Molecular study of aerolysin and cytotonic enterotoxin genes by PCR and colony blot hybridization was performed in 117 strains of Aeromonas spp. isolated from different sources. Homogeneous distribution of these genes in A. hydrophila complex strains was observed. For A. caviae and A. sobria complex strains, aerolysin genes were more frequent than cytotonic enterotoxins genes. Of 64 A. caviae complex strains, only one (1.5%) amplified the 451 bp product for the aer gene, however, the same primers detected a 400 bp product in 50 (78%) strains. This product was sequenced and had two short regions with homology to several hemolysin genes. The genotype aer (+)/aerA(+)/hly (+)/ast (+)/alt (+) was detected in six A. hydrophila strains from food and environmental source. The most common genotype found in A. hydrophila strains was hly (+) (85%) and aerA(+) (78.7%), while in A. caviae complex strains was aerA(+) (32.8%). All A. veronii complex sobria strains were aer (+)/aerA(+). All A. caviae and A. hydrophila were positive when tested with aer probe using the colony blot test. Thirty-seven percent of A. hydrophila and 53% of A. caviae tested were positive for ast probe. Eighty-nine percent of samples were cytotoxic in Vero cells. Our data demonstrated that Aeromonas spp. can harbor and express virulence genes and reinforce the potential of Aeromonas as a human pathogen.

-Background -The diarrheal syndrome is considered a serious public health problem all over the world and is considered a major cause of morbidity and mortality in developing countries. The high incidence of enteroaggregative Escherichia coli in diarrheal syndromes classified as an emerging pathogen of gastrointestinal infections. After decades of study, your pathogenesis remains uncertain and has been investigated mainly using in vitro models of adhesion in cellular lines. Objective -The present study investigated the interaction of enteroaggregative Escherichia coli strains isolated from childhood diarrhea with rabbit ileal and colonic mucosa ex vivo, using the in vitro organ culture model. Methods -The in vitro adhesion assays using cultured tissue were performed with the strains co-incubated with intestinal fragments of ileum and colon over a period of 6 hours. Each strain was tested with three intestinal fragments for each region. The fragments were analysed by scanning electron microscopy. Results -Through scanning electron microscopy we observed that all strains adhered to rabbit ileal and colonic mucosa, with the typical aggregative adherence pattern of "stacked bricks" on the epithelium. However, the highest degree of adherence was observed on colonic mucosa. Threadlike structures were found in greater numbers in the ileum compared to the colon. Conclusion -These data showed that enteroaggregative Escherichia coli may have a high tropism for the human colon, which was ratified by the higher degree of adherence on the rabbit colonic mucosa. Finally, data indicated that in vitro organ culture of intestinal mucosa from rabbit may be used to elucidate the enteroaggregative Escherichia coli pathogenesis.

Finally, our results support the pathogenic potential of Aeromonas emphasising their importance in public health.