Propagation in vitro of Poliomyelitis Viruses VII. pH Change of HeLa Cell Cultures for Assay.

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Abstract
A method is described for use of suspended HeLa cells and phenol red pH indicator for assay of poliomyelitis virus or antibody. A simple medium containing yeast extract and 4% chicken or monkey serum is used to maintain the cultures during incubation with virus or virus-serum mixtures. Infectious virus is revealed by unchanged color of the medium over a 6 day incubation period; neutralization of virus by antibody permits normal cellular metabolism during this period to produce acid with a change in color of the phenol red indicator in the medium to yellow. Evidence is presented for the agreement of results obtained by this method with those of the conventional established cell techniques. The merits of the procedure for assay of poliomyelitis virus and antibody are: a) yeast extract medium is made from materials quickly available and economically purchased; b) cells are washed free of antibody while still attached to the glass surface of the donor bottles so that tedious washing of large numbers of individual tube cultures is avoided; c) savings in time and glassware are conserved by transfer of cells directly to tubes containing incubated virus-serum mixtures, providing tube cultures while eliminating the need for large numbers of additional pipettes for transfer of the incubated virus-serum mixtures to prepared established cell cultures; d) the endpoints of titrations of poliomyelitis virus or antibody are established by inspection with assurance that results can be confirmed by microscopic examination of the tubes.