Diminution de l'activité antibactérienne d'antibiotiques dans des cultures et des infections expérimentales mixtes

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Abstract
Interactions between Staphylococcus aureus and Pseudomonas aeruginosa in the absence and the presence of 4 different antimicrobials in mixed cultures and experimental infections were studied. These 2 bacterial spp., in addition to having different properties, are known to be opportunistic pathogens often present in human microflora. Two main aspects were investigated and they are related to modifications in 2 spp. affecting their equilibrium in the mixed bacterial population and also their pathogenicity markers. Individual growth of S. aureus and P. aeruginosa is not modified in vitro in mixed cultures in the absence of antimicrobials; in vivo, in mouse peritoneal cavity, there is a synergism favorable to S. aureus. In the presence of rifamycin SV and 3 cell wall inhibitors, penicillin G, D-cycloserine and vancomycin. P. aeruginosa protected S. aureus against the inhibitory effect of these antimicrobials in vitro and in vivo. Such results were obtained in different conditions of culture, stationary, shaken and in special apparatuses, an Ecologen and a Chemostat. When any 1 of the antimicrobials was allowed to be in contact for 6-8 h with P. aeruginosa cells in a culture, decrease in their inhibitory effects against S. aureus was observed. These results were supported by microscopical observation. The inhibitory effects of the antimicrobials apparently hindered the formation of toxic products of S. aureus, e.g., .alpha. toxin, and that it was not restored in the presence of P. aeruginosa. P. aeruginosa remained apparently unchanged through all these experiments. The observations may imply that the inhibitory effect of an antimicrobial towards a bacterial species may be significantly decreased in the presence of another species, sometimes present in human microflora.