A Colorimetric Method for the Typing of Coxsackie Viruses of Group B and Certain Members of Group A

Discussion and Summary Preliminary inquiries indicate that the colorimetric method described here is useful for the identification of Coxsackie viruses belonging to group B and may also prove useful for identification of types 11, 13, 15 and 18 of group A. Tissue culture isolates of group A viruses were not available for evaluation of the procedure, but experimental typing of laboratory passage strains gave clear-cut results and no evidence of cross-neutralization. The colorimetric identification test was applied to a total of 112 Coxsackie viruses isolated in monkey kidney cell cultures over a 2-year period. All 16 strains of type B-3, and all 66 strains of type B-5 were identified colorimetrically from the monkey kidney material. Nine of the 16 type B-2 strains, and 3 of the 8 type B-4 strains were presumptively identified from kidney material; however, after a single passage in FL cells, all of the type B-2 and type B-4 strains gave sharp colorimetric end points and were typed with facility. The method was also applied to the identification of 24 completely unknown viruses recovered from throat washings in HeLa cell cultures. Seven of these agents were promptly identified as Coxsackie viruses of the B group, and 17 others were not neutralized by any of the Coxsackie virus immune sera used. Of this Coxsackie-negative group, 10 viruses were later identified as herpes simplex, and 7 still remain unidentified. Passage into FL cells of isolates which cannot be identified from monkey kidney cultures may actually constitute a useful step in the identification of these agents, since those which fail to cause cytopathogenic changes in the FL cells may then be examined in monkey kidney cell cultures against Coxsackie type A-9 immune sera, ECHO virus immune sera, or immune sera against other agents known to cause degeneration in monkey kidney cells but not in HeLa or FL cells (the latter 2 cell types appear to have a similar range of viral susceptibilities). Isolates which cause degeneration in FL cells may then be retested in the colorimetric scheme. The simplicity of testing an isolate by the colorimetric method and relatively high dilutions, at which immune sera may be employed, make repetition of the test a simple and inexpensive procedure. Although a colorimetric identification scheme employing monkey kidney cells might serve to identify Coxsackie group B viruses without the need for passage into FL cells, the colorimetric system employing FL cells has the advantage of conserving available monkey kidney cells for virus isolation work and, in addition, the system may be utilized for identification of four of the group A Coxsackie viruses (types 11, 13, 15 and 18) which do not multiply in monkey kidney cells.