Abstract

Thirty-seven (37) enterococcal isolates were recovered from the skin and intestines of the sea bream (Sparus aurata), the most economically important fish species of the Mediterranean sea from Tunisian fish farming sites, to investigate their antimicrobial potential. All isolates were identified to the species level using genotypic tools. An investigation employing 16S rDNA sequencing in combination with randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) highlighted the predominance of the Enterococcus faecium (46%) and E. faecalis (19%) species. Other species, such as E. sanguinicola (3 strains), E. casseliflavus (3 strains), E. gallinarum (2 strains), Carnobacterium sp. (1 strain), Aerococcus viridans (2 strains) and Vagococcus carniphilus (2 strains) were also identified. The susceptibility to different antibiotics in addition to the antibacterial activities were investigated for all species identified. The isolates were sensitive to vancomycin but were resistant to several antibiotics relevant for therapy in human and animal medicine. Antibacterial profiles assayed against 39 bacterial indicators (including food-borne and fish pathogenic bacteria in aquaculture as well as other spoilage bacteria) showed that 46% of the isolates exhibited a large inhibition spectrum mainly towards Listeria monocytogenes, Staphylococcus aureus, Aeromonas hydrophila, Aeromonas salmonicida, Vibrio anguillarum and Carnobacterium strains. Therefore, highly inhibitory enterococcal strains could potentially be used as probiotics in sea bream and other farming fish fields.

Key words: Enterococcus, lactic acid bacteria, aquaculture, probiotic, sea bream.