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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #329413

Research Project: Integrated Research to Improve On-Farm Animal Health in Salmonid Aquaculture

Location: Cool and Cold Water Aquaculture Research

Title: Exposure to pairs of Aeromonas strains enhances virulence in the Caenorhabditis elegans infection model

item MOSSER, THOMAS - University Of Montpellier
item TALAGRAND, EMILIE - University Of Montpellier
item COLSTON, SOPHIE - University Of Connecticut
item GRAF, JOERG - University Of Connecticut
item FIGUERAS, MARIA JOSE - University Rovira I Virgili
item JUMAS-BILAK, ESTELLE - University Of Montpellier
item LAMY, BRIGITTE - University Of Montpellier

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2015
Publication Date: 11/4/2015
Citation: Mosser, T., Talagrand, E., Colston, S.M., Graf, J., Figueras, M., Jumas-Bilak, E., Lamy, B. 2015. Exposure to pairs of Aeromonas strains enhances virulence in the Caenorhabditis elegans infection model. Frontiers in Microbiology. 6:1218. doi: 10.3389/fmicb.2015.01218.

Interpretive Summary: Aeromonas infections in fish are often caused by co-infections of multiple Aeromonas species. In this study, we investigated if the virulence of naturally occurring infection pairs is enhanced during co-infections. We obtained six pairs of Aeromonas isolates obtained from patients and established a virulence model in Caenorhabditis elegans. Infections were performed either as single or mixed infections and the median time to death (TD50) was determined for all pairs (both naturally occurring and experimental). Two of the natural pairs and five of the other pairs showed enhanced TD50, suggesting mixed infections were more virulent than single infections. The virulence enhanced pairs, always consisted of different species. The content of virulence-associated gene failed to explain virulence synergy although some virulence–associated genes present in some strains were absent from their companion strain (e.g., T3SS). Synergistic virulence observed between infectious isolates shows that it is important to consider Aeromonas infections at the community level and multiple isolates need to be obtained when identifying pathogens.

Technical Abstract: Aeromonad virulence remains poorly understood, and is difficult to predict from strain characteristics. In addition, infections are often polymicrobial (i.e., are mixed infections), and 5 -10% of such infections include two distinct aeromonads, which has an unknown impact on virulence. In this work, we studied the virulence of aeromonads recovered from human mixed infections. We tested them individually and in association with other strains with the aim of improving our understanding of aeromonosis. Twelve strains that were recovered in pairs from six mixed infections were tested in a virulence model of the worm Caenorhabditis elegans. Nine isolates were weak worm killers (median time to death, TD50, greater than or equal to 7 days) when administered alone. Two pairs showed enhanced virulence, as indicated by a significantly shortened TD50 after co-infection vs. infection with a single strain. Enhanced virulence was also observed for five of the 14 additional experimental pairs, and each of these pairs included one strain from a natural synergistic pair. These experiments indicated that synergistic effects were frequent and were limited to pairs that were composed of strains belonging to different species. The genome content of virulence-associated genes failed to explain virulence synergy, although some virulence-associated genes that were present in some strains were absent from their companion strain (e.g., T3SS). The synergy observed in virulence when two Aeromonas isolates were co-infected stresses the idea that consideration should be given to the fact that infection does not depend only on single strain virulence but is instead the result of a more complex interaction between the microbes involved, the host and the environment. These results are of interest for other diseases in which mixed infections are likely and in particular for water-borne diseases (e.g., legionellosis, vibriosis), in which pathogens may display enhanced virulence in the presence of the right partner. This study contributes to the current shift in infectiology paradigms from a premise that assumes a monomicrobial origin for infection to one more in line with the current pathobiome era.