Numerical taxonomy of lactobacilli surviving radurization of meat

Abstract

All 113 Gram-positive, catalase-negative, rod-shaped bacteria isolated from radurized (5 kGy) minced beef were homofermentative, aciduric and belonged to the sub-genus Streptobacterium. Lactobacillus sake was the predominant species with 100 strains being identified as such. Two strains produced L(+)-lactic acid and were identified as L. farciminis. Three strains were indistinguishable from L. curvatus and 8 strains were intermediate between L. sake and L. curvatus and were designated L. sake/curvatus. Numerical taxonomy by unweighted pair-group average linkage analysis revealed the existence of 5 clusters of these strains. Two isolates and all 7 reference strains were unclustered. Cluster 1 consisted of 4 sub-clusters (a-d) which all showed greater than 90% similarity. Clusters 2–5 were observed at 89, 88, 86 and 84% respectively. Cluster 1 contained 86 of the isolates which were split into sub-cluster: 1a (12 strains); 1b (44); 1c (17); 1d (13). All strains were closest to L. sake except for one strain in cluster 1b and five in cluster 1c which were L. sake/curvatus. Cluster 2 contained 9 isolates of which 3 strains were designated L. curvatus, one L. sake/curvatus and five L. sake. Cluster 3 contained 7 strains, 6 of which were L. sake and one was L. sake/curvatus. Cluster 4 contained 6 strains, all of which were L. sake and finally, cluster 5 contained 3 strains, two of which were L. sake whilst the other produced L(+)-lactic acid and was designated L. farciminis. DNA mol% G+C studies done on 7 L. sake isolates indicated a very wide range (37.3−44.2 mol%) of values within these strains.