Variation of Micrococcus tetragenus.

Numerous recent studies suggest that the phenomenon of microbic dissociation or dissociative variation is exceedingly complex and involves more than the M, S, R, and G phases so extensively studied during the past decade. Evidence at present indicates that in addition to these so-called phase-transformations, another form of variation exists which involves even greater biologic differences. In studies on a strain of Micrococcus tetragenus obtained from a patient I have encountered more than 13 different forms and have isolated and studied 10 of the fairly stable ones. 1 They were named according to pigment-production, colonial morphology and cell-morphology as follows: mucoid-yellow, yellow, mucoid-white, white, mucoid-pink, pink, pink-yellow, brown, translucent, and a bacillary form. There was evidence of frequent change from one form to another and each of the forms except the bacillary one was related to the other directly or indirectly by antigenic similarity. In attempting to correlate the 10 different forms with the M, S, R, and G forms of other bacteria, difficulty was encountered in the fact that 3 mucoid forms existed in the same presumed dissociative pattern. Furthermore no true R forms had been noted during 18 months of observation. The recent appearance of distinctly rough, dry, crinkled, and adherent pink colonies among smooth pink ones when an 8-month-old-broth-culture of the latter form was plated, suggested the possibility that at least 2 kinds of bacterial variation exist. The white, yellow, pink, pink-yellow, and brown forms may represent distinct variants or may even be regarded as antigenically specific types analogous to those existing, for example, among pneumococci, whereas the mucoid-white, mucoid-yellow, mucoid-pink, and rough-pink forms may represent cultural phases of the respective types. The place of the translucent form and its occasional lytic colonies in the scheme has not yet been determined.