Ultrastructure of small colony variants of a methicillin-resistant Staphylococcus aureus.

aureus was isolated from two patients in the same ward of the Seattle Veterans Administration Hospital. This strain, called the Seattle variant, caused a fatal pneumonia in one of the patients and has been the object of a detailed laboratory investigation (R. J. Bulger, Ann. Internal Med., 67:81, 1967). The results indicate that the mechanism of resistance to methicillin was probably a combination of "innate" resistance and excessive penicillinase production, similar to that of methicillinresistant strains studied elsewhere in the world (S. Seligman, J. Gen. Microbiol. 42:315, 1966; Y. Chabbert et al., Rev. Franc. Etudes Clin. Biol. 10:495, 1965; C. F. Gravenkemper, J. L. Brodie, and W. M. M. Kirby, J. Bacteriol. 89: 1005, 1965; K. Ericksen and I. Ericksen, Acta Pathol. Microbiol. Scand. 62:399, 1964). The great majority of cells surviving exposure to high concentrations of methicillin were small colony variants similar to those described by Seligman. They often became visible to the naked eye as tiny, translucent colonies only after 36 to 48 hr of incubation at 37 C. This small colony variant seems to bear a close resemblancetotheantibioticresistant G forms reported in the past with a variety of organisms (R. Wise and W. Spink, J. Clin. Invest. 33:1611, 1964). In the literature on G forms, there has been a debate as to whether