Limitations of general growth media in fish analysis and research for SSOs
Broekaert, K.; Heyndrickx, M.; Devlieghere, F.; Vlaemynck, G. (2010). Limitations of general growth media in fish analysis and research for SSOs, in: Exchange: open innovation for feed, food and health, where industry and academia meet. In: (2010). Exchange: open innovation for feed, food and health, where industry and academia meet. Food2Know: Ghent. , more |
| Abstract | Microbiological (quality) control of fresh fish and research for specific spoilage organisms (SSOs) is necessary for the determination of the remaining shelf-life. The total viable count for microbiological fish quality is often performed on Plate Count Agar (PCA) (Oxoid) according to the International Standard Organisation (ISO 8552 and 17410). However, since it is known that PCA has some limits, the isolation of genera/species present on various fish was compared on PCA and on different other media.A study based on 11 fish species during processing and storage on ice was performed. Fish samples were collected from a distribution centre of a large supermarket and were incubated during regular time intervals on different media, namely PCA, marine agar (Difco), Long and Hammer medium and Lyngby Iron Agar. After incubation, a replication technique was used to compare the capability of colonies to grow on the different media. The colonies not growing on one of the media were collected, purified and DNA was extracted. The strains were clustered by rep-PCR analyses and identified based on partial 16S rRNA and gyrB gene sequencing. A DGGE analysis based on the V3 region of the 16S rRNA gene was performed from plateswabs of the different media.Colony counts on PCA are for practically all fish samples much lower compared to the other media. Identification of the not growing colonies indicate that several members of the genera Photobacterium, Shewanella, Brochothrix, Pseudomonas, Psychrobacter, Flavobacterium and Pseudoalteromonas are not able to grow on all media. Some of these species are known to be important for fish quality and shelf-life, such as the SSOs of fish (eg. Photobacterium phosphoreum, Shewanella baltica, Brochothrix thermosphacta). The DGGE profiles confirm that the bacterial community growing on the various media clearly differs from each other. Especially the profiles obtained from PCA are different from those from the salt-containing media. The profiles between the marine media however are often similar. We can conclude that it needs to be considered that the use of only one medium (especially PCA) is in most cases not adequate for quality control of fish samples throughout the supply chain until the end of shelf-life. |
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