COMPARATIVE STUDIES ON THE COLONIAL VARIANTS OF THE SMITH STRAIN OF STAPHYLOCOCCUS AUREUS

The Smith strain of staphylococcus, used in many laboratories for "virulence" studies, is known to be ge~~etically unstable. The strain has been shown to have more than one colony type, and reports concerning its phage type and its phage typability have been conflicting. In our work, four "Smith" strains were obtained from four dirferent laboratories. Three of these strains produced three colony variants - compact, diffuse, and mucoid - whereas the fourth strain produced only the co~npact and mucoid variants. Results with phage typing were not always consistent but the compact colony variants were much more susceptible to lysis by phage than the parent strains, and the diffuse variants appeared to be completely resistant to lysis by phage. The resi~lts confirm reports in the literature that the Smith strain is genetically unstable and gives rise to a number of different colony forms with varying phage susceptibility. The Smith strain of Staphylococcz~s aurezls, isolated in 1930 froin an osteomyelitis patient, has beell maintained by repeated transfer on laboratory culture media with occasioilal passage through mice (6). Its high virulence for mice has made it particularly useful for laboratory aninla1 experiments, and reports concerning its colonial and other characteristics have been published (3, 5, 6). It has been apparent for solne time that the strain is genetically unstable and that "Smith" strains in different laboratories are not always identical in all respects. Smith and Dubos (6), for example, reported the strain to be phage type 44A/42E, whereas others have reported it at non-typable. Further, it has been sl~own that there are colonial variants within the strain itself. Hunt and Moses (2) fouild two distinct colony types when they used a soft agar medium containing norilia1 serum, a coinpact colony (C) and a diffuse one (D). Finkelstein and Sulkill (1) found that the compact variant produced both mucoid (M) and non-mucoid colonies on solid nlediuin but that the colonies were indistinguisl~able in seruin soft agar. The purpose of the present re~ort is to describe the results of soine of our studies with the colonial variants ol a number of Sinith strains.