title: In vivo exposure of Mytilus edulis to living enteric bacteria: a threat for immune competency?
abstract: Mussels are widespread in coastal environments and experience various physical, chemical, and bacteriological conditions. Owing to the increase of coastal urbanization, mussels are now commonly exposed not only to indigenous bacteria, but also to enteric bacteria originating from pulsed and chronic sewage discharges into coastal environments. Due to its broad resilience to environmental variations, the blue mussel Mytilus edulis is commonly used as an indicator of environmental quality in bio-monitoring programs. However, since mussel immune system capabilities may be affected by the presence of exogenous fecal bacteria in coastal seawater subjected to sewage discharges, we aimed to determine the effect of in vivo bacterial challenges on mussels' immune competency by using two exogenous enteric bacterial strains, Escherichia coli and Enterococcus faecalis, and an indigenous bacterial strain Vibrio splendidus (as control). Bacterial strains were tested individually, by injection into the posterior adductor muscle at three different cell densities (10(2), 10(3), and 10(4) cells). Unlike classic in vitro experiments using higher bacterial concentrations, neither the enteric bacteria nor the indigenous strain induced significant increase or decrease of either cell-mediated (phagocytosis, reactive oxygen species, and NO(x) production) or humoral components (prophenoloxidase-like, acid phosphatase, and L-leucine-aminopeptidase production) of the immune system. This study demonstrates that, at low concentrations, E. coli and E. faecalis do not represent an additional threat that could impair M. edulis immune competency and, as a consequence, its potential of survival in coastal areas subjected to sewage discharges.
authors.affiliation: Institut des sciences de la mer de Rimouski, UQAR, 310 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada.
authors.forename: Sophie
authors.initials: S
authors.lastname: Gauthier-Clerc
authors.forename: Isabelle
authors.initials: I
authors.lastname: Boily
authors.forename: Michel
authors.initials: M
authors.lastname: Fournier
authors.forename: Karine
authors.initials: K
authors.lastname: Lemarchand
mesh_terms: D000818:Animals; D004755:Enterobacteriaceae / Q000472:pathogenicity*; D013293:Enterococcus faecalis / Q000472:pathogenicity; D004926:Escherichia coli / Q000472:pathogenicity; D005243:Feces / Q000382:microbiology; D056724:Immunity, Humoral; D007121:Immunocompetence; D007931:Leucyl Aminopeptidase / Q000378:metabolism; D049880:Mytilus edulis / Q000276:immunology* / Q000382:microbiology* / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D010587:Phagocytosis; D017382:Reactive Oxygen Species / Q000378:metabolism; D012722:Sewage; D014733:Vibrio / Q000472:pathogenicity; D014871:Water Microbiology
chemical_list: D017382:Reactive Oxygen Species; D012722:Sewage; D009569:Nitric Oxide; D007931:Leucyl Aminopeptidase