Exotoxin profiles of clinical isolates of Aeromonas hydrophila

Molecular characterization of clinical isolates of Aeromonas species from Malaysia

Background

Aeromonas species are common inhabitants of aquatic environments giving rise to infections in both fish and humans. Identification of aeromonads to the species level is problematic and complex due to their phenotypic and genotypic heterogeneity.

Methodology/Principal Findings

Aeromonas hydrophila or Aeromonas sp were genetically re-identified using a combination of previously published methods targeting GCAT, 16S rDNA and rpoD genes. Characterization based on the genus specific GCAT-PCR showed that 94 (96%) of the 98 strains belonged to the genus Aeromonas. Considering the patterns obtained for the 94 isolates with the 16S rDNA-RFLP identification method, 3 clusters were recognised, i.e. A. caviae (61%), A. hydrophila (17%) and an unknown group (22%) with atypical RFLP restriction patterns. However, the phylogenetic tree constructed with the obtained rpoD sequences showed that 47 strains (50%) clustered with the sequence of the type strain of A. aquariorum, 18 (19%) with A. caviae, 16 (17%) with A. hydrophila, 12 (13%) with A. veronii and one strain (1%) with the type strain of A. trota. PCR investigation revealed the presence of 10 virulence genes in the 94 isolates as: lip (91%), exu (87%), ela (86%), alt (79%), ser (77%), fla (74%), aer (72%), act (43%), aexT (24%) and ast (23%).

Conclusions/Significance

This study emphasizes the importance of using more than one method for the correct identification of Aeromonas strains. The sequences of the rpoD gene enabled the unambiguous identication of the 94 Aeromonas isolates in accordance with results of other recent studies. Aeromonas aquariorum showed to be the most prevalent species (50%) containing an important subset of virulence genes lip/alt/ser/fla/aer. Different combinations of the virulence genes present in the isolates indicate their probable role in the pathogenesis of Aeromonas infections.

Ulinastatin alone does not reduce caspase 3-mediated apoptosis in protease-positive Aeromonas hydrophilia-induced sepsis

BACKGROUND/PURPOSE

To evaluate the effect of ulinastatin, a protease inhibitor, on survival and apoptosis in protease-positive Aeromonas hydrophilia (PPAH)-induced sepsis.

METHODS

Thirty mice were randomly allocated to receive intraperitoneal injection of either phosphate buffered saline (PBS) (control mice, n = 10) or PPAH (PPAH mice, n = 20). After 30 minutes, control mice received an additional intraperitoneal PBS injection, 10 PPAH mice received intraperitoneal PBS injection (non-treated PPAH mice), and the remaining 10 PPAH mice received an intraperitoneal injection of ulinastatin (ulinastatin-treated PPAH mice).

RESULTS

Survival at 24 hours was 100% in control mice, and 35% (p < 0.05) in PPAH mice; the survival rate in non-treated and ulinastatin-treated PPAH mice were 30% and 40% (p > 0.05), respectively. The thymus weight (mg) decreased significantly in PPAH mice (51.1 +/- 14.9) compared to control mice (69.7 +/- 14.4; p < 0.001); there was no difference between ulinastatin-treated (52 +/- 13.9; p > 0.05) and non-treated PPAH mice (50.4 +/- 16). The thymus gland cell count reduced significantly in PPAH mice (8.1 +/- 4.7 x 10(7)) compared to control mice (12.8 +/- 6.6 x 10(7); p < 0.01), and immunofluorescence analysis demonstrated that the reduced cells were mostly CD4+ CD8+, in contrast to the increase in CD4+ CD8- cells. There was no difference in cell count between ulinastatin-treated (8.7 +/- 4.9 x 10(7)) and non-treated PPAH mice (7.4 +/- 4.6 x 10(7); p > 0.05). Caspase 3-mediated apoptosis was not detectable in control mice in contrast to the pronounced manifestation in PPAH mice.

CONCLUSION

PPAH-induced sepsis has a high mortality that is related to lymphocyte apoptosis. Ulinastatin alone does not significantly reduce caspase 3-mediated lymphocyte apoptosis.

Clinical significance and distribution of putative virulence markers of 116 consecutive clinical Aeromonas isolates in southern Taiwan

OBJECTIVES

The objectives of this study were to elucidate the clinical manifestations of Aeromonas infections and the association of putative virulence genes with clinical invasiveness.

METHODS

116 consecutive clinical Aeromonas isolates collected from July 1999 to June 2001 in a medical center in southern Taiwan were included. All isolates were identified by biochemical phenotyping and their genomic sequences encoding eight putative virulence factors, including cytolytic enterotoxin (AHCYTOEN), aerolysin (aerA), hemolysin (hlyA), heat-labile enterotoxin (alt), heat-stable enterotoxin (ast), and components of type III secretion system (ascV, aexT and ascF-ascG) were analyzed using polymerase chain reaction and colony blot hybridization. The association of clinical diseases of the patients with the putative virulence genes in the isolates was analyzed.

RESULTS

Sixty-two percent of Aeromonas isolates caused clinically evident infections, of which the major clinical manifestations were primary bacteremia (40%), followed by soft tissue infections (27%), and hepatobiliary tract infections (15%). Liver cirrhosis (36%), malignancy (25%), and hepatobiliary diseases (13%) were the major underlying diseases in patients with Aeromonas bacteremia. The majority (64%) of patients with Aeromonas hepatobiliary infections had underlying hepatobiliary diseases, whereas 71% of those with soft tissue infections had antecedent water- or soil-related injuries. The crude fatality rate for Aeromonas infections was 26%. Aeromonas hydrophila complex was the most common (52%) of the three major complex groups investigated, followed by Aeromonas sobria complex (24%) and Aeromonas caviae complex (23%). None of the eight putative virulence factors was associated with invasiveness or bacteremia.

CONCLUSIONS

Primary bacteremia, soft tissue infections, and hepatobiliary tract infections are the three major clinical manifestations of invasive Aeromonas infections in southern Taiwan. This study found no association between the presence of AHCYTOEN, aerA, hlyA, alt, ast, ascV, aexT or ascF-ascG genes in Aeromonas isolates and the development of extra-intestinal infections or bacteremia.

Niche-specific association of Aeromonas Ribotypes from human and environmental origin

A total of 88 Aeromonas isolates from distinct locations and sources (39 from extraintestinal infections, 31 from diarrhoeic, ten from non-diarrhoeic faeces, all human, and eight from fresh water) were subjected to phenospecies identification, serotyping, ribotyping and detection of some virulence markers. The strains belonged to four different phenospecies marked by 19 O serogroups and 38 ribotypes. No strong correlation between these parameters was found, and no group, as defined by the typing methods, could be characterized with a particular set of virulence markers. There was a clear association of ribotypes with the source of the strains. Cluster analysis allowed the identification of a complex of ribotypes belonging to distinct but related sources, including clinical and environmental isolates. These results suggest that ribotyping may be an epidemiological tool suitable for the study of Aeromonas infections.

Assays of hemolytic toxins

The ability to produce a cytolytic toxin contributes to the success of many organisms in a particular niche by such diverse means as lysis of a phagolysosomal membrane of the macrophage by hemolysin from the intracellular parasite Trypanosoma cruzi, disruption of leukocyte activity by the Escherichia coli hemolysin, and destruction of invading bacteria by hemolysin from the annelid Glycera dibranchiata. The relative contribution of erythrocyte lysis to survival of the cytolysin producer is still under investigation. Nevertheless, the hemolytic phenotype is both a powerful tool for identifying novel cytolysins and a convenient marker for studying cytolytic activity in established toxins.