- Volume 83, Issue 2, 1974

Summary: Deoxyribonucleic acid reassociation was used to assess divergence in species of Citrobacter and Citrobacter-like strains. Typical strains of Citrobacter freundii were highly related. Antigenically atypical strains and most biochemically atypical strains showed a lower, but species level, of relatedness to typical C. freundii. Four additional relatedness groups were detected. One of these corresponded to C. diversus, including Levinea malonatica. A second contained L. amalonatica.

A third group contained two indole+ strains which exhibited only 40 to 50 % relatedness to other groups of Citrobacter. The fourth group contained H2S −, lysine+ organisms that are more closely related to Serratia than to Citrobacter.

Summary: Eighteen cariogenic streptococcal strains identified as members of Streptococcus mutans (Clarke, 1924) were compared on the basis of biochemical tests, mannitol-1-phosphate dehydrogenases, DNA base compositions and DNA base sequence homologies. Some slight biochemical differences were found which correlated with the large differences in DNA base composition and sequence heterology which exist among these strains. All strains could be assigned to one of four groups based on these biochemical and genetic differences. Furthermore, these four groups correlated with four serological groups described by Bratthall (1970). It is proposed to divide S. mutans into four subspecies: S. mutans subsp. mutans, the type subspecies, has a guanine-cytosine (G-C) of 36 to 38 mol % and belongs to Bratthall serological group c; S. mutans subsp. rattus subsp. nov. has 41 to 43 mol % G-C, belongs to Bratthall group b, and can be distinguished from the other subspecies by its production of ammonia from arginine; S. mutans subsp. cricetus subsp. nov. has 42 to 44 mol % G-C, belongs to Bratthall group a, and can be distinguished by its lack of growth in air; S. mutans subsp. sobrinus subsp. nov. has 44 to 46 mol % G-C, belongs to Bratthall group d, and can be distinguished by its failure to ferment raffinose.

SUMMARY: We tested 151 strains representing the genera Nocardia and Gordona, the taxon ‘Mycobacterium’ rhodochrous and a collection of strains isolated from bagasse for their in vitro susceptibility to 52 antimicrobial agents by using the impregnated filter-paper disc method. The ‘bagasse’ isolates were resistant to most of the antimicrobial agents but the nocardiae, gordonae and rhodochrous groups formed a series with increasing sensitivity. The nocardiae were inhibited by low concentrations of a number of antibiotics, notably erythromycin, miconazole, gentamycin and tobramycin, which may be of value in treating Nocardia infections. Certain antibiotics, at suitable concentrations, provided data of value for the classification and identification of nocardioform bacteria.