Plaque formation by non-cytopathogenic bovine virus diarrhea strains

A rapid, quantitative assay for titration of bovine virus diarrhoea-mucosal disease virus

An end point dilution microtitration assay is described that can be used for the titration of both cytopathic and non-cytopathic isolates of bovine virus diarrhoea-mucosal disease virus. Indirect immunofluorescence is used to detect infected MDBK cells in the wells of Terasaki plates. The virus titre is derived from the number of uninfected wells, using the Poisson distribution. The assay is simple, fast and economical. Titres of cytopathic virus determined by the microtitration assay and standard plaque assay are equivalent.

Studies on the interaction between coxsackievirus A9 and HeLa cells. I. Plaque-forming ability of coxsackievirus A9 in HeLa cell cultures

Most of the coxsackievirus A9 (CA 9 virus) including the prototype strain formed plaques in HeLa cell monolayers under agar overlay, although they showed little or no cytopathogenicity under fluid medium. These viruses were isolated or passaged in primary cynomolgus monkey kidney (MK) cell cultures, and the infectivity of any strain in terms of plaque-forming units was much higher in MK cells than in HeLa cells, even after plaque purification of the virus in HeLa cell cultures. CA 9 virus contained in the original throat swabs as well as some clones obtained by plaque purification in MK cells failed to form plaques in HeLa cells, but virus preparations obtained after several undiluted passages through MK cells included plaque-formers in HeLa cells, suggesting that such plaque (HeLa)-forming viruses may have developed at a certain rate during multiplication of the original non-plaque (HeLa)-forming virus population in MK cells. Out of four lines of HeLa cells examined, two, including a clonal line S3, failed to support plaque formation by CA 9 virus.