Distribution of virulence factors and molecular fingerprinting of Aeromonas species isolates from water and clinical samples: suggestive evidence of water-to-human transmission

Abstract

A total of 227 isolates of Aeromonas obtained from different geographical locations in the United States and different parts of the world, including 28 reference strains, were analyzed to determine the presence of various virulence factors. These isolates were also fingerprinted using biochemical identification and pulse-field gel electrophoresis (PFGE). Of these 227 isolates, 199 that were collected from water and clinical samples belonged to three major groups or complexes, namely, the A. hydrophila group, the A. caviae-A. media group, and the A. veronii-A. sobria group, based on biochemical profiles, and they had various pulsotypes. When virulence factor activities were examined, Aeromonas isolates obtained from clinical sources had higher cytotoxic activities than isolates obtained from water sources for all three Aeromonas species groups. Likewise, the production of quorum-sensing signaling molecules, such as N-acyl homoserine lactone, was greater in clinical isolates than in isolates from water for the A. caviae-A. media and A. hydrophila groups. Based on colony blot DNA hybridization, the heat-labile cytotonic enterotoxin gene and the DNA adenosine methyltransferase gene were more prevalent in clinical isolates than in water isolates for all three Aeromonas groups. Using colony blot DNA hybridization and PFGE, we obtained three sets of water and clinical isolates that had the same virulence signature and had indistinguishable PFGE patterns. In addition, all of these isolates belonged to the A. caviae-A. media group. The findings of the present study provide the first suggestive evidence of successful colonization and infection by particular strains of certain Aeromonas species after transmission from water to humans.

FIG. 1.

Hue diagram showing levels of N-acyl homoserine lactones (AHLs) produced by different species groups of Aeromonas. AHL production was detected using the C. violaceum CV026 biosensor strain. The different numbers of plus signs indicate the different levels of AHLs produced as described in Materials and Methods.

FIG. 2.

PFGE profile analysis of three sets of water and clinical Aeromonas isolates that had indistinguishable PFGE patterns. Lane A, AA-14 (A. caviae-A. media group); lane B, AA-15 (A. caviae-A. media group); lane C, AA-16 (A. caviae-A. media group); lane D, NM-14 (A. caviae-A. media group); lane E, NM-35 (A. caviae-A. media group); lane F, NM-33 (A. caviae-A. media group); lane G, NM-22 (A. caviae-A. media group).

FIG. 3.

Western blot analysis for detection of the secreted T6SS effectors Hcp and VgrG2-VgrG3 in culture supernatants of seven water and clinical Aeromonas isolates. Lane A, A. hydrophila SSU (positive control); lane B, NM-14 (A. caviae-A. media group); lane C, NM-22 (A. caviae-A. media group); lane D, NM-33 (A. caviae-A. media group); lane E, NM-35 (A. caviae-A. media group); lane F, AA-14 (A. caviae-A. media group); lane G, AA-15 (A. caviae-A. media group); lane H, AA-16 (A. caviae-A. media group).