Use of conventional biochemical tests and analyses of ribotype patterns for classification of micrococci isolated from dairy products

Various methods were used to study 42 Gram-positive cocci belonging to the family of Micrococcaceae and isolated from dairy products. Only a few strains could be identified using the ATB 32 biochemical micromethod rapid gallery system (API). All strains were subjected to conventional biochemical tests. The results were then analysed by a numerical method using the Sokal–Michener similarity coefficient. The 42 strains were distributed into 10 clusters at the Euclidean distance of 3·2. Most (75%) of the isolates were identified at the species level, but Micrococcus luteus could not be differentiated from Mc. lylae within the Micrococcus genus. An identification method based on the analysis of ribotype patterns was then applied to the isolates and these were compared with the patterns of collection strains. Cellular DNA was cleaved by the restriction enzymes SacI and KpnI and probed with the peroxidase-labelled 16S+23S rRNA of Escherichia coli. Ribotype patterns were analysed using a Dice coefficient and the unweighted pair group method using arithmetic averages, making dendrogram construction possible. Of the strains investigated, >84% were characterized to the species level. The remaining strains were found to belong to the Arthrobacter group or were atypical Micrococcus species. Of the isolates, 52% belonged to Micrococcus luteus, 17% were identified as Kocuria varians and 7% were assigned to the Brachybacterium genus.