A frequency matrix for probabilistic identification of some bacilli

A matrix comprising frequencies for positive results for 44 Bacillus taxa for 30 characters has been constructed. The 44 taxa include most of the common species and several clusters of environmental isolates including those described as B. firmus-B. lentus intermediates. The tests, which were chosen for their high diagnostic value, included some of the traditional tests used for identification of bacilli supplemented with a range of sugar fermentations and other characterization tests. The matrix was evaluated by identifying hypothetical median organisms, cluster representatives and a panel of 23 reference strains. All reference strains achieved Willcox probabilities above 0.995. Fifty-eight environmental isolates were also subjected to the 30 tests and identification was attempted. Forty-one strains (70%) achieved a Willcox probability greater than 0.95, which was considered an acceptable identification, and were assigned to 12 taxa. If the SE of taxonomic distance was also considered in the identification score (an acceptable value being less than 7.0), the number of acceptable identifications was reduced to 34 (59%). It was encouraging that bacteria from garden soils identified to the common species such as B. subtilis, B. cereus and B. licheniformis whereas some of the bacteria from an estuarine habitat were identified as species such as B. firmus which are normally identified with that habitat.