Effect of mycoplasma on growth of canine distemper virus in Vero cells.

It was recognized that Vero cells which had once been used for a titration of canine distemper virus (CDV) had been contaminated with mycoplasmas. Then mycoplasmas were examined for effect on the growth of CDV in these cells. Mycoplasma orale was isolated from 2 of 4 sublines of Vero cells. It could replicate in Mycoplasma-free Vero cells without causing CPE. When these cells were infected with CDV at a low multi-plicity of infection (MOI), decreased yields (1 log) in Mycoplasma-infected cells were observed from 72 to 120 hours after virus inoculation. When MOI was high, the growth of virus was delayed in Mycoplasma-infected cells by about 24 hours. On the other hand, no significant difference was seen between CDV titers assayed in Mycoplasma-free and those assayed in Mycoplasma-infected Vero cells. These results suggest that M. orale used may have a low ability to inhibit the growth of CDV. A decreased yield was seen, irrespective of arginine concentration (0.5 and 0.1 mM) in the medium. When antiserum against M. orale was added to Mycoplasma-infected cultures, virus titers approximated the levels obtained in Mycoplasma-free cultures.