DIVERSITY OF LACTIC ACID BACTERIA ASSOCIATED WITH FISH AND FISHFARM ENVIRONMENT, ESTABLISHED BY AMPLIFIED RIBOSOMAL DNA RESTRICTION ANALYSIS (ARDRA)

Unité de Virologie et d'Immunologie Moléculaires, Institut National de la Recherche Agronomique, Centre de Recherches de Jouy-en-Josas, France; Laboratoire Départemental des Landes (LD40), Mont-de-Marsan, France; Groupement de Défense Sanitaire Aquacole d'Aquitaine, Mont-de-Marsan, France; Unité d'Ecologie Microbienne des Insectes et Interactions hôte-pathogène, Unité Mixte de Recherche, Institut National de la Recherche Agronomique, Université Montpellier II, Montpellier, France

^* To whom correspondence should be addressed. Email: christian.michel{at}jouy.inra.fr.

	Abstract

Lactic acid bacteria have become a major source of concern for aquaculture in recent decades. In addition to true pathogenic species of worldwide significance, like Streptococcus iniae and Lactococcus garvieae, several species have been reported to produce occasional fish mortalities in limited geographic areas and many unidentifiable or ill-defined isolates are regularly isolated from fish or fish products. To clarify the nature and prevalence of different fish-associated bacteria belonging to the lactic acid bacteria group, a collection of 57 isolates of different origins was studied and compared with a set of 22 type strains using amplified ribosomal DNA restriction analysis (ARDRA).

Twelve distinct clusters were delineated on the basis of ARDRA profiles and were confirmed by the sequencing of sodA and 16S rRNA genes. These clusters included the following: Lactococcus raffinolactis, L. garvieae, L. lactis, S. iniae, S. dysgalactiae, S. parauberis, S. agalactiae, Carnobacterium spp, Enterococcus "faecium" group, a heterogeneous Enterococcus-like cluster comprising indiscernible representatives of Vagococcus fluvialis or the recently recognized V. carniphilus, V. salmoninarum and Aerococcus spp. Interestingly, the L. lactis and L. raffinolactis clusters appeared to include many commensals of fish, so that opportunistic infections caused by this species cannot be disregarded. The significance for fish populations and fish food processing of 3 or 4 genetic clusters of uncertain or complex definition, namely Aerococcus and Enterococcus, should be established more accurately.