Analysis Of The Bacterial Community Structure Change In Tilapia During Spoilage And Isolation, Identification And Control Of Spoilage Organisms

Tilapia is the most important fish among China aquaculture and exports. Due to the short shelf life of live tilapia and tilapia product, further development of tilapia culture has been limited. Because microorganisms are the major cause of fish spoilage, studies of the bacterial community structure change during spoilage and quorum-sensing system of spoilage organisms will facilitate us to find a way to lengthen the shelf life of fresh fish and reduce economic loss.In this study, fresh tilapia was selected and treated by two different processing methods (3 replicates): removing bone and intestinal tract (JY) and only removing bone (QY). The samples were stored at 4°C and 25°C, respectively. Each treatment was sampled at 1, 3, 7, 14 days. Using DGGE, plate count, pH test, and isolation and identification of spoilage bacteria, the change of bacterial community structure during spoilage was explored.The DGGE analysis showed that the bacteria in group JY were confined intoα-proteobacteria,β-proteobacteria,γ-proteobacteria, Firmicutes and unclassified. Among them,γ-proteobacteria was the predominant bacteria. The bacteria in group QY were mainly proteobacteria, Firmicutes and Unclassified.It has been reported that the DGGE technology can only detect the bacteria of more than 1% of the total bacterial community. However, some pathogenetic bacteria in fish are lower than 1% of the total bacteria, thus isolation and identification of bacteria using the traditional pure culture approach was supplementary to the DGGE analysis. The samples stocked at 25°C for 3 days were subjected to isolation and identification of spoilage organisms. A total of 23 bacterial strains were isolated and classified into Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria.N-Acyl homoserine lactones (AHLs) have been identified to regulate the expression of pathogenetic genes in Gram-negative bacteria by quorum-sensing system. AiiAB546 from Bacillus sp. B546, an N-acylhomoserine lactone lactonase, was used to study the relationship between AHLs and expression of genes related with spoilage. M. morganii, Proteus vulgaris, and Flavobacteriacea sp. playing key roles in fish spoilage and having ability to produce AHLs were selected as spoilage organisms. Results showed that AiiAB546 could degrade the AHLs produced by Flavobacteriacea sp., resulting in lower extracellular proteinase activity. AiiAB546 had no effect on the AHLs produced by M. morganii and P. vulgaris.