A taxonomic study of Chryseobacterium species in meat

English: Microbial diversity in a food complicates the prediction or measurement of the effect of specific micro-organisms on a perishable food commodity stored under different conditions. Gram-negative yellow-pigmented colonies belonging to the Flavobacteriaceae family are often present when total numbers on food samples are investigated. Changes in the taxonomy of flavobacteria since its inception in 1923 have, however, complicated the identification of these bacteria. Many organisms previously regarded as Flavobacterium have been found to belong to several new genera in the family Flavobacteriaceae. With the introduction of a chemotaxonomic approach and molecular techniques such as rRNA sequencing, it is now possible to refine the differentiation between closely related genera. Chromosomal DNA characteristics further enhance accurate differentiation between various species. This study used a polyphasic taxonomic approach that included a combination of phenotypic and genotypic testing methods in order to characterise and classify Gram-negative yellow-pigmented strains isolated from raw chicken, red meat and fish. During this study 129 Gram-negative yellow-pigmented pure cultures were isolated from raw chicken, red meat and fish samples. Protein fingerprint profiles and long chain fatty acid analyses revealed that the majority of organisms belonged to the genus Chryseobacterium. The 16S rRNA sequence and DNA-DNA hybridisation methods were used to give the relationship between test strains and the reference strains of various species in the genus. Several isolated strains from the chicken, red meat and fish could be equated with C. balustinum (2), C. defluvii (16), C. scophthalmum (4) or C. gleum (2) strains. A few strains (9) did not show any affiliation with any reference strain. Two new Chryseobacterium species, however, have been proposed from the findings of this study namely Chryseobacterium vrystaatense sp.nov.,which is comprised of the type strain R-23566 (= LMG 22846T) and 36 strains isolated from raw chicken samples. Strains showed strong DNase- and also urease and lecithinase activity but were not capable of starch and tyrosine hydrolysis. The mol % G + C of R-23566 was 37.6 %. The second new species, Chryseobacterium piscium sp. nov., comprised four strains which were obtained from marine fish, with R-23621 as the type strain. The G + C mol % was 33.6 %. This group was psychrotrophic in that they grew within 24 hours at 4 °C but very poorly at 32 °C. In order to establish the source of potential Chryseobacterium contamination, different areas and processing stages in the chicken abattoir were sampled. Chryseobacterium species contributed to 8.3 % of the total bacterial count on whole birds in this study. It was evident that the washing processes lowered the total counts on carcasses. A significant increase in the total bacterial counts, as well as total Chryseobacterium counts was reported and Chryseobacterium species were found to represent between 20 and 25 % of the total population after portioning procedures during this study. Live chickens as source of Chryseobacterium contamination should be investigated in future.