Subinhibitory concentrations of erythromycin reduce pneumococcal adherenceto respiratory epithelial cells in vitro

We have investigated the influence of subinhibitory concentrations of eryth romycin on the interaction between Streptococcus pneumoniae and human respi ratory epithelial cells. Confluent in vitro cell cultures were inoculated a nd incubated for 24 h. Erythromycin significantly reduced adherence of the pneumococci after 4 h and 24 h: 4.0% +/- 0.7% (mean +/- S.E.M.) Of the pneu mococci adhered to the epithelial cells in medium with erythromycin, compar ed with 7.7% +/- 0.8% in medium without erythromycin (P = 0.002) after 4 h, and the corresponding values after 24 h were 24.2% +/- 5.3% and 38.4% +/- 5.0%, respectively (P = 0.038). Disruption of epithelial integrity by S. pn eumoniae, measured as the decrease in transepithelial electrical resistance , was delayed in the presence of erythromycin. Neither addition of erythrom ycin to the culture medium nor infection of the cell cultures with pneumoco cci significantly affected secretion of interleukin-8 by the epithelial cel ls. Addition of erythromycin to a pneumococcal suspension in cell culture m edium without respiratory epithelial cells almost completely prevented the release of pneumolysin. We conclude that erythromycin at subinhibitory conc entrations reduces the adherence to and disruption of respiratory epithelia l cells by S. pneumoniae, possibly by interfering with pneumolysin release.