Backgrounds:
Bacterial superinfection is a medically well-accepted phenomenon though
experimental-based evidence is scarce. Epidemiologically, respiratory
infections with respiratory syncytial virus (RSV) are associated with
infections by S. pneumoniae. As bacterial adherence to the local
epithelium is considered a prerequisite for infection, we focus on the effect of
RSV pre-infection of the epithelium on pneumococcal adherence in both a
quantitative and qualitative way.
Methods:
Human respiratory epithelial cells were pre-infected with RSV serotype
A. Several clinically isolated pneumococcal serotypes were tested in a
Cytofluor-based adherence assay. Bacteria and cells were visualized by
fluorescence microscopy and scanning electronmicroscopy.
Results:
Pneumococci vary in their capacity to adhere, depending on the serotype
and growth-phase. Apart from adherence, pneumococcal invasion can be detected
as assessed by scanning electronmicroscopy.With RSV pre-infection, enhanced
pneumococcal adherence was measured. This effect was dependent on the dosage of
virus, the pneumococcal serotype and the time interval after viral infection of
the cells. By fluorescence microscopy, most pneumococci were seen attached to
the contours of the cells. Remarkably, massive amounts of pneumococci adhered
to syncytia, typically formed during RSV infection.
Conclusion and discussion:
RSV preinfection can induce enhanced adherence of pneumococci to respiratory epithelial cells.This might be one of the mechanisms underlying bacterial superinfection. Differences of enhanced adherence between serotypes suggest a selective receptor mediated binding. The presence of syncytia contributes significantly to the amount of adherence. Further study is needed to reveal the molecular backgrounds of this increased adherence and invasion as well as the relevance of these results