[Study of the bactericidal activity of pristinamycin ].

In vitro, the bacteriostatic activity of pristinamycin varies according to the relative proportion of its two components, P I and P II, following a bell-shaped curve reflecting their synergistic effect. In vivo, the pharmacological profile of both components could be different and their synergistic bacteriostatic effect may therefore vary. This led us to study the bactericidal activity of different concentrations of the two components. Strains of staphylococci of varying sensitivity to macrolides and to each of the two components, P I and P II, were tested in our laboratory. We studied the bactericidal effect of various relative concentrations of both components tested in nutrient broth and transferred on nutrient agar, using Millipore membranes (according to the modified Chabbert's technique of cellophane transfer). We showed that the synergistic bactericidal activity of the two components yields a curve quite different from that observed for their bacteriostatic activity: the bactericidal activity is excellent, irrespective of the relative proportions of P I and P II in the medium. For all tested strains and relative proportions of both components, the MIC/MBC ratio is equal to one. We can therefore conclude that the determination of the SBA is useless and can assume that, as far as the serum levels of both components are above the MIC for the pathogenic strains, the blood is bactericidal. We have previously shown that transient incubation of P II on its target (50 S ribosomal sub-unit) led to a binding strength which is high (bactericidal activity) and prolonged ("bacteriopause").