Bacterial Adherence to Virus-Infected Cells: A Cell Culture Model of Bacterial Superinfection

MDCK cells (a line of stable canine kidney cells) infected with influenza A/NWS/33 virus (a neurotropic variant of the Wilson Smith strain) were tested with 18 selected bacterial species to determine whether mammalian cells become susceptible to bacterial adherence as a result of virus infection. Cell monolayers were washed and examined microscopically for adherence. Bacteria of only two of 18 species were seen to adhere to the infected cells: a group B Streptococcus and Streptococcus sanguis. Control monolayers were negative for adherence. Pretreatment of virus-infected cultures with mouse ascitic fluid containing antibody to influenza A virus completely blocked adherence of the bacteria. Further testing with the strains representative of the five serotypes of group B Streptococcus disclosed that adherence occurred with types Ia, Ic, and II, but not with types Ib and III.