Aeromonas hydrophila vacuolating activity in the Caco-2 human enterocyte cell line as a putative virulence factor

Potential pathogenicity ofAeromonas hydrophilacomplex strains isolated from clinical, food, and environmental sources

Aeromonas are autochthonous inhabitants of aquatic environments, including chlorinated and polluted waters, although they can also be isolated from a wide variety of environmental and clinical sources. They cause infections in vertebrates and invertebrates and are considered to be an emerging pathogen in humans, producing intestinal and extra-intestinal diseases. Most of the clinical isolates correspond to A. hydrophila, A. caviae, and A. veronii bv. Sobria, which are described as the causative agents of wound infections, septicaemia, and meningitis in immunocompromised people, and diarrhoea and dysenteric infections in the elderly and children. The pathogenic factors associated with Aeromonas are multifactorial and involve structural components, siderophores, quorum-sensing mechanisms, secretion systems, extracellular enzymes, and exotoxins. In this study, we analysed a representative number of clinical and environmental strains belonging to the A. hydrophila species complex to evaluate their potential pathogenicity. We thereby detected their enzymatic activities and antibiotic susceptibility pattern and the presence of virulence genes (aer, alt, ast, and ascV). The notably high prevalence of these virulence factors, even in environmental strains, indicated a potential pathogenic capacity. Additionally, we determined the adhesion capacity and cytopathic effects of this group of strains in Caco-2 cells. Most of the strains exhibited adherence and caused complete lysis.

Detection of Aeromonas hydrophila in liquid media by volatile production similarity patterns, using a FF-2A electronic nose

A technique for rapid detection of pathogenic microorganisms is essential for the diagnosis of associated infections and for food safety analysis. Aeromonas hydrophila is one such food contaminant. Several methods for rapid detection of this pathogen have been developed; these include multiplex polymerase chain reaction assays and the colony overlay procedure for peptidases. However, these conventional methods can only be used to detect the microorganisms at high accuracy after symptomatic onset of the disease. Therefore, in the future, simple pre-screening methods may be useful for preventing food poisoning and disease. In this paper, we present a novel system for the rapid detection of the microorganism A. hydrophila in cultured media (in <2 h), with the use of an electronic nose (FF-2A). With this electronic nose, we detected the changes of volatile patterns produced by A. hydrophila after 30 min culture. Our calculations revealed that the increased volatiles were similar to the odours of organic acids and esters. In future, distinctive volatile production patterns of microorganisms identified with the electronic nose may have the potential in microorganism detection.

Phylogenetic analysis of intestinal bacteria and their adhesive capability in relation to the intestinal mucus of carp

AIMS

The aims of the present study are to characterize the intestinal microbial community displaying a high-adhesive capability in fish, and to evaluate the relationship between mucosal adhesion of intestinal bacteria and fish health and disease.

METHODS AND RESULTS

A total of 707 aerobic bacteria isolated from carp intestine that were maintained under either feeding (feeding group) or no-feeding (no-feeding group) conditions and were performed adhesive assay. Isolates were divided into three categories on the basis of adhesive capability: high-, medium-, and low- adhesive capabilities. The average proportions of isolates with high-adhesive capability in the feeding and no-feeding groups were 30% and 32%, respectively. A phylogenetic analysis using a partial 16S rRNA gene demonstrated that most isolates with high-adhesive capability in both groups were classified as belonging to an Aeromonas group, and populations of isolates within high- and low-adhesive categories were markedly different.

CONCLUSIONS

Intestinal bacteria with a high-adhesive capability in relation to intestinal mucous always colonize on the surface of intestinal mucosa and grow in the intestinal tract of feeding carp. The adhesive capability of intestinal bacteria is essential for colonization and growth in the intestinal tract of fish.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results indicate that members of the Aeromonas group with adhesive capability always colonize on the surface of intestinal mucosa.

Interactions of clinical and environmental Aeromonas isolates with Caco-2 and HT29 intestinal epithelial cells

AIM

Evaluation of adherence and invasion of Aeromonas spp. to human colon carcinoma cell lines Caco-2 and HT29 and assessment of cytotoxic activity.

METHODS AND RESULTS

A number of 27 strains of Aeromonas caviae and 23 strains of Aeromonas hydrophila was analysed. All strains were capable to adhere to sub-confluent monolayers of Caco-2 and HT29 cell types, presenting aggregative and diffuse adherence patterns cells, respectively. In the cytotoxic assays all strains showed cytopathic and/or cytotoxic activities to Vero cells. The evaluation of the tetrazolium salt (MTT test) reduction capability was carried out in Vero, Caco-2, and HT29 cells. MTT test showed that Vero cell line was the most sensitive cell type. In the invasion test, 13 strains were analysed on Caco-2 and HT29 monolayers. Only two (15%) of the 13 strains, A. hydrophila and A. caviae species, both isolated from vegetables were invasive to Caco-2 cells. No strains were able to invade the HT29 cells.

CONCLUSIONS

A. hydrophila and A. caviae isolated from human diarrhoeic faeces, vegetables, and water, were able to adhere to and produce cytotoxic/cytopathic effects in intestinal epithelial cell lines.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of Aeromonas spp. in food and water samples expressing virulence factors suggest that these sources may act as dissemination vehicles of human pathogen with implication in the public health.

Prevalence of environmental Aeromonas in South East Queensland, Australia: a study of their interactions with human monolayer Caco-2 cells

AIMS

To investigate the prevalence of Aeromonas in a major waterway in South East Queensland, Australia, and their interactions with a gut epithelial model using Caco-2 cells.

METHODS AND RESULTS

A total of 81 Aeromonas isolates, collected from a major waterway in South East Queensland, Australia, were typed using a metabolic fingerprinting method, and tested for their adhesion to HEp-2 and Caco-2 cells and for cytotoxin production on Vero cells and Caco-2 cells. Aeromonas hydrophila had the highest (43%) and Aeromonas veronii biovar sobria had the lowest (25%) prevalence. Four patterns of adhesion were observed on both HEp-2 and Caco-2 cell lines. Representative isolates having different phenopathotypes (nine strains) together with two clinical isolates were tested for their translocation ability and for the presence of virulence genes associated with pathogenic Escherichia coli. The rate and degree of translocation across Caco-2 monolayers varied among strains and was more pronounced with LogA pattern. Translocation was associated with the adherence of strains to Caco-2 cells microvilli, followed by internalization into Caco-2 cells. Two Aer. veronii biovar sobria strains were positive for the presence of heat-labile toxin genes, with one strain also positive for Shiga-like toxin gene.

CONCLUSIONS

Pathogenic strains of Aeromonas carrying one or more virulence characteristics are highly prevalent in the waterways studied and are capable of translocating across a human enterocyte cell model.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates that Aeromonas strains carrying one or more virulence properties are prevalent in local waterways and are capable of translocating in a human enterocyte cell culture model. However, their importance in human gastrointestinal disease has yet to be verified under competitive conditions of the gut.