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

Dwarf-colony (D) variants of Staphylococcus aureus are relatively widespread etiological agents of bovine mastitis in Israel. D strains grow 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 thiamineauxotrophs 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, we 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.