Conditions Contributing to Streptococcal Virulence

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Abstract
This paper presents details of an attempt (1) to increase the virulence of a strain of greening (later, indifferent) streptococcus from endocarditis by a series of passages through mice; (2) to ascertain to what relative extent such increase was due to intra-phasic modifications as contrasted with inter-phasic. The expt. was. so designed that the K to S transformation occurred in the bodies of the mice The chief results were: An S-phase organism of low virulence isolated from a patient was transformed by the usual selective cultural methods to R phase. With this culture, rajns. were started. After 38 serial passages the original virulence of the R form (M.L.D., 0.7 ml. of broth culture) was increased to an approximate M.L.D. of 0.000,001 ml. in the resulting S. During the first 11 passages the culture transformed from R to S, passing through the intermediate colony forms, RS and SR. During these 11 passages the virulence increased from 0.7 ml. to 0.005 ml., the latter being approx. the virulence of the first isolated S form. From the 12th to the 38th passage, inclusive, the organisms remained constantly within the S range but, during this time, the virulence further increased from 0.005 ml. to 0.000,001 ml. The total increase in virulence during the period of R to S transformation was 140 times; that occurring within the S phase alone (range of intra-phasic variation) was about 5,000 times. The total increase over the 38 passages was about 700,000 times and required 114 days. It was concluded that, in the strain of streptococcus studied, potential virulence was determined by the dissociative culture phase, but that actual virulence, particularly maximal virulence, was controlled by environmental influences (in this case, mouse environment) operating on the organisms existing within the range of a single culture phase,[long dash]in this case, the S. It is as important to learn what characteristics of bacteria are not controlled by dissociative changes as it is to know what characteristics are so controlled.