Sub-inhibitory and post-antibiotic effects of spiramycin and erythromycin on Staphylococcus aureus.
The antibacterial responses of clinical isolates of Staphylococcus aureus to spiramycin and erythromycin were compared. Conventional MICs showed erythromycin-sensitive strains to be 16-32 times less sensitive to spiramycin. MBCs were only four to eight times higher for spiramycin. Erythromycin resistant S. aureus were more frequently encountered. Concentrations of both macrolides at 1/4 MIC produced antibacterial effects. Post-antibiotic effects were more marked with spiramycin. After 3 h exposure to 4 x MIC of antibiotic the delay in regrowth of S. aureus was 5 h for erythromycin and 9 h for spiramycin. In a continuous cultivation model, spiramycin produced an inhibitory effect on S. aureus for 12 h whereas the effect of erythromycin was only apparent for 6 h. In conclusion, spiramycin is more active against staphylococci in vitro than would be expected by its modest MICs.
Webster
C
C
Department of Microbiology, Queen's Medical Centre, Nottingham, UK.
Ghazanfar
K
K
Slack
R
R
D004352:Drug Resistance, Microbial; D004917:Erythromycin / Q000494:pharmacology*; D007933:Leucomycins / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D009391:Nephelometry and Turbidimetry; D013211:Staphylococcus aureus / Q000187:drug effects*
D007933:Leucomycins; D004917:Erythromycin