Comparison of the effects of macrolides, amoxicillin, ceftriaxone, doxycycline, tobramycin and fluoroquinolones, on the production of pneumolysin by Streptococcus pneumoniae in vitro.

OBJECTIVES To compare the effects of subinhibitory concentrations of amoxicillin, ceftriaxone, azithromycin, clarithromycin, erythromycin, telithromycin, clindamycin, ciprofloxacin, moxifloxacin, tobramycin and doxycycline on pneumolysin production by a macrolide-susceptible strain and two macrolide-resistant strains [erm(B) or mef(A)] of Streptococcus pneumoniae. METHODS Pneumolysin was assayed using a functional procedure based on the influx of Ca(2+) into human neutrophils. RESULTS Only the macrolides/macrolide-like agents caused significant attenuation of the production of pneumolysin, which was evident with all three strains of the pneumococcus. CONCLUSIONS Macrolides, at sub-MICs, but not other classes of antibiotic, subvert the production of pneumolysin, even in the presence of (and irrespective of the mechanism of) macrolide resistance in S. pneumoniae.