Epidemiological and biochemical studies on thiamine less dwarf colony variants of Staphylococcus aureus as etiological agents of bovine mastitis

Dwarf colony (D) variants of S. aureus are relatively widespread etiological agents of bovine mastitis in Israel. D strains grown on ordinary solid nutrient media with pinpoint, transparent colonies. An epidemiological study indicated that these variants are more communicable than normal (N) S. aureus strains. Biochemically, several types of metabolic defects have been demonstrated among the D strains: strains from one herd were pantothenate less, most of the other isolates were thiamine less, and a few of them were both thiamine and pantothenate less. Among the thiamine auxotrophs were a few (from one herd) which were unable to concentrate thiamine thiazole, whereas all of the other strains required thiamine pyrimidine (HMP) in the form of pyrophosphate (HMP PP). At least some of these D strains were defective in three functions: concentrative uptake of HMP, phosphorylation of HMP, and phosphorylation of HMP monophosphate. Since mutants with normal growth occurred readily, it was assumed that the information for these three functions exists on a polycistronic operon. Quantitative requirements for HMP PP varied highly among the D strains, and other data also indicated that HMP PP requiring strains had not developed from a common source.