Inhibition of bactericidal capacity in mice after administration of Newcastle disease virus

Modification of susceptibility to Klebsiella pneumoniae during murine cytomegalovirus infection

The effect of murine cytomegalovirus (MCMV) infection on susceptibility to bacterial infection was studied in mice by a combination of intraperitoneal (ip) inoculation of a sublethal dose of MCMV with subsequent ip challenge of 2 X 10(3) cfu of a strain of Klebsiella pneumoniae (KP). When given alone, KP produced a mortality of 30-40%. Mortality was increased when KP was given 1 to 7 days after MCMV injection with the peak increase at the 4th to 5th day when 100% mortality occurred. Virus levels in various organs of mice infected with MCMV alone, or superinfected with KP did not differ. Bacterial counts on the other hand, showed that increased mortality in mixed MCMV and KP infected mice was due to an uncontrolled growth of bacteria at the site of primary lodgment, i.e., the peritoneum, and severe systemic infection. Neutrophil response to growth of KP during the first 3 days of bacterial infection was defective in MCMV infected mice. While the initial clearance of KP from the blood was more efficient in MCMV infected mice, probably due to activated reticuloendothelial function, it did not protect the mice against KP infection. Using the in vivo model, it was shown that poor neutrophil response and possibly other defective neutrophil functions were responsible for increased mortality to KP infection in MCMV infected mice.

Invasiveness of Salmonella typhimurium in HEp-2 cell cultures preinfected with Coxsackie B 1 virus

The influence of infection of HEp-2 cells with Coxsackie B 1 virus on the invasiveness of Salmonella typhimurium has been studied. The bacterial invasiveness was significantly increased in the cell cultures incubated with virus before bacterial inoculation. This effect was a function of time after introduction of virus into the cell cultures and the concentration of virus. The increase in bacterial invasiveness was observed before production of infectious virus particles and before development of cytopathogenic effect was evident. Two strains of non-invasive Escherichia coli did not show invasiveness after the virus treatment of the cells. The results indicate a specific mechanism for the interaction.