Original Article

Annals of Microbiology

, Volume 63, Issue 2, pp 733-744

First online:

Characterisation and identification of spoilage psychotrophic Gram-negative bacteria originating from Tunisian fresh fish

  • Mouna BoularesAffiliated withUnité de Recherche “Sciences et Technologies des Aliments”, École Supérieure des Industries Alimentaires de Tunis (ESIAT) Email author 
  • , Mélika MankaiAffiliated withUnité de Recherche “Sciences et Technologies des Aliments”, École Supérieure des Industries Alimentaires de Tunis (ESIAT)
  • , Chedia AouadhiAffiliated withLaboratoire de Microbiologie, “Groupe bioprocédés”, Institut Pasteur de Tunis (IPT)
  • , Ben Moussa olfaAffiliated withUnité de Recherche “Sciences et Technologies des Aliments”, École Supérieure des Industries Alimentaires de Tunis (ESIAT)
  • , Mnasser HassounaAffiliated withUnité de Recherche “Sciences et Technologies des Aliments”, École Supérieure des Industries Alimentaires de Tunis (ESIAT)

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Abstract

The contamination of fresh fish by spoilage bacteria is undesirable, particularly when Gram-negative bacteria, which produce thermo-resistant protease and lipase, can grow. The purpose of the present work was, therefore, to isolate and identify psychrotrophic Gram-negative (Psy G(-)) bacteria, isolated from 80 samples of 12 species of wild and aquacultured fresh seafood, by biochemical and molecular methods using 16S rRNA gene sequencing. Twenty-eight identified strains were studied to evaluate their catalase, nitrate reductase, lipolytic and proteolytic activities, as well as growth ability, at different temperatures, pH and NaCl concentrations. Among 150 Psy G(-) strains, the most dominant species found were: Pseudomonas fluorescens, Aeromonas hydrophila, Pseudomonas putida and Photobacterium damselae. All strains of Psy G(-) had catalase activity and were able to reduce nitrates to nitrites. Proteolytic activity on milk and on gelatin agar was demonstrated for the majority of the isolates. However, extracellular proteolytic activity as assessed by the azocasein method wasn’t very high in all the strains. Lipolytic activity, as assessed by the agar method, showed that 92.9 % of strains could hydrolyse egg yolk, against 82.1 % and 57 % that could hydrolyse Tween 20 and Tween 80, respectively.

Keywords

Fresh fish Psychrotrophic Gram-negative bacteria Proteolytic activity Lipolytic activity