| Abstract: | The aim of the study was to assess the of chosen antibiotics in subinhibitory concentrations (sub-MIC) on the sensitive of Staphylococcus aureus cells to phagocytosis and killing by rabbit granulocytes. The following antibiotics were used: cloxacillin, cefadroxil, cefuroxim, cefotaxim, gentamicin, netilmicin, lincomicin, doxycycline and riphamicin. A total of 144 S. aureus strains with varied sensitivity to these antibiotics were selected for the study. The experiment used granulocytes isolated from rabbit blood and S. aureus strains incubated for 18 h in TSB broth containing antibiotics in the concentrations of 0.1 MIC, 0.2 MIC and 0.5 MIC, and in the antibiotics-free medium. Phagocytosis was assessed by the method of differential staining with acridine orange and crystal violet, allowing simultaneous determination of phagocytised and killed S. aureus cell counts. The findings revealed that the culture of S. aureus in the presence of all the antibiotics used in subinhibitory concentrations increased significantly the susceptibility of most S. aureus strains to phagocytosis and killing by granulocytes. The above effect usually occurred in the concentrations of 0.1 MIC (54.2%), more seldom in 0.2 MIC (13%) and 0.5 MIC (15% of strains). Each group of S. aureus contained some which showed no change in susceptibility following culture with the chemotherapeutic agents in subinhibitory concentrations (26.3%). Insensitive strains to the subinhibitory effects were equally common among susceptible (27%), intermediate (23%) and resistant (26%) strains of S. aureus to the antibiotics used. No statistically significant reduction was noted in phagocytosis or killing by rabbit granulocytes. No correlation was observed between the susceptibility to the subinhibitory effects of the antibiotics involved and their biochemical mechanisms. |
