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 Ca2+ 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.