Cytopathic effect of Haemophilus ducreyi for human foreskin cell culture

An explant adult foreskin cell culture (FS2-3) was compared with human lung carcinoma cell culture (A549) with regard to the ability of Haemophilus ducreyi to produce a cytopathic effect. The survival of H. ducreyi for up to 26 days in FS2-3 cells was far greater than in any previously described in-vitro culture system. H. ducreyi survived for up to 7 days in A549 cells. The H. ducreyi cells grew and formed "fungal-like" microcolonies on the eukaryotic monolayer. Portions of the microcolonies remained attached despite extensive washing. Transmission electronmicroscopy indicated that, at 48 h after infection, the H. ducreyi cells did not penetrate the FS2-3 cells but they were closely associated with them; there was only a 2-5 nm gap between the H. ducreyi cell wall and the FS2-3 membrane. The virulent H. ducreyi strains RO18 and 35,000 produced a cytopathic effect on FS2-3 cells that did not appear to be due to a soluble toxin. These strains did not produce any CPE on A549 cells. H. influenzae and the avirulent H. ducreyi strain CIP542, inoculated in the same concentration and incubated for the same length of time, did not produce CPE on FS2-3 cells. This study demonstrated that the use of FS2-3 foreskin cell culture provided an in-vitro approach for evaluating the cytopathic effect of virulent H. ducreyi whereby, unlike in other in-vitro systems, viability of the micro-organism could be readily maintained.