The taxonomy and spoilage characteristics of Flavobacteriaceae isolates from food

English: Frequent reports of yellow-pigmented Gram-negative rods being encountered during routine bacteriological analyses of milk and milk products, meat, canned products and surface waters, accentuate the universal distribution of Flavobacteriaceae. Many organisms previously regarded as Flavobacterium have been found to belong to several new genera in the family Flavobacteriaceae. The introduction of a chemotaxonomic approach and molecular techniques such as rRNA sequencing, has made it possible to refine the differentiation between closely related genera. Although Flavobacteriaceae are widely distributed in soil and plants, their presence and roles in these environments has received less attention in South Africa. The first purpose of this study was to investigate the presence of Flavobacteriaceae from eight different vegetables and the surrounding soil in which the vegetables were planted; yellow pigmented Gram-negative bacteria were isolated from the samples and examined for the presence of Flavobacteriaceae. The second part of this study was to taxonomically re-define flavobacterial dairy isolates from previous studies using newer phenotypic procedures, including the BIOLOG system and also genotyping techniques such as 16S rRNA sequencing. Phenotypic tests were used for the preliminary grouping of isolates. The BIOLOG Microplate system showed that most “flavobacterial” isolates from vegetables were highly related to the genus Sphingobacterium, whereas isolates from soil were related to Chryseobacterium gleum/indologenes. Most of the dairy isolates identified with this method were closely related to the genera Chryseobacterium and Empedobacter. The 2001 database of the BIOLOG system currently in use, is however, incapable of identifying all Flavobacteriaceae genera and species since no new additions have been made and it is also not possible to manually do so. Isolates were subsequently subjected to the 16S rRNA sequencing technique which was able to verify and differentiate organisms identified by the BIOLOG Microplate system. Because of poor quality DNA, the two soil isolates could not be identified with this method. Fourteen of the 18 dairy isolates that underwent sequencing were highly related to the genus Chryseobacterium while four isolates were identified as E. brevis. The possible spoilage characteristics of the Flavobacteriaceae isolates in this study were also evaluated using the BIOLOG system. It became clear that they could utilize certain carbohydrates, carboxylic acids, amino acids and polymers that could contribute to spoilage defects of food by creating off-odours, off-tastes, sliminess and bitterness of specific foods.