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.
Highlights
The frequent usage of antimicrobial agents has led to the development of multiple antibiotic resistance (MAR) in bacteria and has reduced the efficacy of antibiotic treatment for human and animal diseases (Tendencia and de la Pena, 2001; Pandiyan et al, 2013)
Antibacterial profiles assayed against 39 bacterial indicators 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
The results of the alignements allowed the classification of nine intestinal strains as E. faecium, seven strains as E. faecalis, three strains as E. casseliflavus, one strain as Enterococcus gallinarum, two strains as E. sanguinicola, one strain as Carnobacterium sp., two strains as Aerococcus viridans and two other strains as Vagococcus carniphilus
Summary
The frequent usage of antimicrobial agents has led to the development of multiple antibiotic resistance (MAR) in bacteria and has reduced the efficacy of antibiotic treatment for human and animal diseases (Tendencia and de la Pena, 2001; Pandiyan et al, 2013). The culture practices for most farmed fish species are mostly semi-intensive or intensive and farms are often affected by widespread antibiotic resistance in pathogens (Aeromonas hydrophila, Aeromonas salmonicida, Edwardsiella tarda, Edwardsiella icttaluri, Vibrio anguillarum, Vibrio salmonicida, Pasteurella piscida and Yersinia ruckeri), which are currently treated with antibiotics (Ben Kahla-Nakbi et al, 2009). Replacing drugs with effective and inexpensive probiotics is necessary to avoid resistance in fish farming sites and antibiotic residues in fish flesh destined for human consumption (Rengpipat et al, 2008)
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