Characterization ofPseudomonasspp. Associated with Spoilage of Gilt-Head Sea Bream Stored under Various Conditions

Abstract

The population dynamics of pseudomonads in gilt-head sea bream Mediterranean fish (Sparus aurata) stored under different conditions were studied. Phenotypic analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins were performed to identify a total of 106 Pseudomonas strains isolated from S. aurata stored under different temperatures (at 0, 10, and 20°C) and packaging conditions (air and a modified atmosphere of 40% CO 2 -30% N 2 -30% O 2 ). Pseudomonas lundensis was the predominant species, followed by Pseudomonas fluorescens, while Pseudomonas fragi and Pseudomonas putida were detected less frequently. Fluorescent Pseudomonas strains dominated under air conditions, while proteolytic and less lipolytic strains dominated under modified-atmosphere packaging. Different storage conditions appear to govern the selection of pseudomonads in gilt-head sea bream fish.It is well known that fish spoilage is primarily due to (i) autolysis, (ii) bacterial growth and metabolism resulting in the formation of off-flavor compounds, and (iii) chemical oxidation of lipids. Among these reasons, microbiological activity is by far the most important factor influencing fish quality (22). However, not all microorganisms in seafood are equally important for quality changes. Fish feeding habits, geographical location, season, sea temperature, type of fish, place in which the fish were harvested, and storage conditions, including temperature and composition of the packaging atmosphere, determine the spoilage domains of specific spoilage organisms (SSO) (22,36).Photobacterium phosphoreum, Shewanella putrefaciens, Brochothrix thermosphacta, Pseudomonas spp., Aeromonas spp., and lactic acid bacteria were found to be members of the microbial association in fish from temperate waters (12, 32). However, among these, only S. putrefaciens was the SSO of marine cold-water fish stored in ice, while P. phosphoreum was the SSO of fish stored under modified-atmosphere conditions. On the other hand, Pseudomonas spp. and Shewanella spp. were found to be the SSO in fish obtained from Mediterranean Sea temperate waters and stored in ice aerobically (32). In comparison to data for meat and meat products (19,45,57), identification and characterization of SSO in fish under different storage conditions have not been sufficiently studied. This situation is especially evident with Pseudomonas spp., a group with high heterogeneity and biodiversity within species and/or subspecies. Furthermore, many pseudomonad groups have no clear taxonomic status or natural relationships with other genera (44,47,48,49).For both of the reasons mentioned above, the use of conventional phenotypic methods can offer only limited results (6, 9, 42). In contrast, molecular methods are powerful tools not only for identification at the species level but also for strain characterization (7,14,29,30,63). Although molecular fingerprinting methods have been successfully applied for bacteria of medical interest in epidemiological studies, they are not al...

Incidence of indicator organisms, opportunistic and pathogenic bacteria in fish

“…The duplicated plates were incubated at 10 o C for 7 days for psychrophilic/psychrotrophic and 25 o C for 48 hours for mesophilic counts. All plates with colony forming units between 30 and 300 were recorded [15,16,17,18].…”

Microbial communities and biogenic amines of crucian carp (Carassius auratus) fillets during partial freezing and chilled storage

“…A large shift was observed in the microbial communities of chilled samples on day 12, in which Pseudomonadaceae reached 64.19% and became the predominant bacterial family while the proportion of Aeromonadaceae and Shewanellaceae decreased to 12.68 and 7.88%, respectively. This may be attributed to the inability of the microbiota to compete with Pseudomonadaceae, which has the ability to grow well under anaerobic conditions, [28] and the selective action of storage conditions. In comparison, the composition of bacterial communities on day 40 was similar to that on day 35.…”

Bacteriological and physicochemical qualities of traditionally dry-salted Pebbly fish (Alestes baremoze) sold in different markets of West Nile Region, Uganda

“…have a psychrophilic nature and are regarded as part of the natural flora of fish. The species can form aldehydes, ketones, esters and sulphides following food spoilage, causing odours described as fruity and rotten (Tryfinopoulo et al, 2002). The isolation of Pseudomonas spp from the collected fish samples is of high importance because this bacterium plays considerable role as a potential pathogenic bacteria for human and as an indicator of food spoilage.…”