Characterisation, identification and technological properties of psychotrophic lactic acid bacteria originating from Tunisian fresh fish
Résumé
One hundred sixty psychrotrophic lactic acid bacteria (LAB) isolated from wild and aquacultured fresh fish were identified by biochemical and molecular methods using 16S-23S rRNA spacer analysis and 16S rDNA sequencing. LAB strains were characterised according to their technological properties including acidifying capacity, antibiotic resistance and proteolytic, lipolytic and enzymatic activities, as well as antimicrobial activities, against pathogenic and spoilage bacteria in order to select the most suitable strains for use as starter cultures in the biopreservation of fresh fish and seafood products. The majority of strains displayed antimicrobial activities against pathogenic bacteria (Salmonella arizonae, Staphylococcus aureus, Listeria monocytogenes, Pseudomonas aeruginosa, Escherichia coli and Aspergillus flavus) and the dominant psychrotrophic Gram-negative bacteria in fresh fish (Pseudomonas fluorescens, Aeromonas hydrophila, Pseudomonas putida and Photobacterium damselae). A total of 39 isolates of LAB isolates having the most important antimicrobial activities were selected for further properties. Low proteolytic and lipolytic activities were detected for all strains using azocasein methods and fish fat, respectively. Moreover, all strains showed acidifying activity by reducing pH to less than 4.38 at 37C after 72 h. Finally, all studied LAB were resistant to penicillin, gentamicin, colistin, ciprofloxacin, norfloxacin, nalidixic acid, erythromycin, tetracycline and streptomycin. PRACTICAL APPLICATIONS The paper presents the identification and the technological properties of lactic acid bacteria (LAB) including antimicrobial activity against pathogenic and spoilage bacteria in order to select the most suitable strains for use as starter cultures in the biopreservation of fresh fish and seafood products. Considering this, assessment of the effect of inoculation of selected LAB on microbiological and physicochemical properties of fresh fish stored at chilled temperature is necessary to guarantee adequate fresh seafood products safety. Therefore, these analyses can lead to develop better biopreservation strategy for fresh fish by the use of selected LAB strains.