[Evaluation of interactions between strains of S. aureus isolated from different clinical specimens with peripheral...

The aim of this study was to investigate the interactions occurring between peripheral blood phagocytes and strains of S. aureus isolated from different clinical specimens (blood, respiratory tract, pus). To evaluate the sensitivity of microorganisms to bactericidal activity of phagocytes, monocytes and granulocytes separated from peripheral blood by standard density gradient and by counter-current centrifugal elutriation were incubated with suspensions of opsonized bacteria. In parallel, the viability of phagocytes was examined by flow cytometry, and the ability of bacteria to trigger reactive oxygen intermediates (ROI) production was evaluated by chemiluminescence measurement. To investigate efficiency of phagocytosis, bacteria were labelled with fluorescein isothiocyanate (FITC) and the percentage of cells containing FITC-labelled bacteria was analysed by flow cytometry. The data obtained show that strains of S. aureus originated from different clinical specimens, differ in their sensitivity to bactericidal activity of phagocytes--strains isolated from the blood show the highest, but strains isolated from respiratory tract show the lowest sensitivity for killing. These strains differ too in their ability to trigger monocyte CL response. Contrary, there was no difference in toxicity of bacteria against phagocytes. Strains isolated from peripheral blood showed significant negative correlation between the ability to trigger CL response and toxicity against phagocytes.