[Effects of subinhibitory concentrations of antibiotics on the virulence of group A hemolytic Streptococci].

We have investigated the influence of subinhibitory concentrations of chloramphenicol, erythromycin, penicillin G and gentamicin on the phagocytosis and the virulence in the mouse of strains of group A beta-haemolytic streptococci. In most cases, an increase of the phagocytosis and a decrease of the virulence were shown. The maximum effect have been observed in concentration ranging from 1/2 to 1/8 of the respective MIC. In one strain, the virulence was enhanced in the presence of 1/2 and 1/4 MIC of chloramphenicol and 1/2 of erythromycin, in spite of the fact that the phagocytosis was increased in these concentrations of drugs. The importance of hyaluronic acid as virulence factor has been investigated and discussed.