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M Lebrun

Publications and source records attributed to M Lebrun.

47 records · Page 3Linked to original sources

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Demography↗

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Increased in vitro sensitivity of Candida albicans to amphotericin B when grown in mixed culture with Escherichia coli.

The growth of Candida albicans was inhibited by some Escherichia coli strains both in conventional batch cultures and also in a chemostat under conditions of constant addition of fresh medium. Concentrations of 0.2 microgram amphotericin B per millilitre and of 2 microgram nystatin per millilitre, which caused a slight inhibition of C. albicans in pure culture, exerted a strong fungicidal effect when the yeast was placed in mixed cultures with certain strains of E. coli. Candida albicans cells, inhibited by either E. coli or in mixed culture with polyene antibiotics, appeared larger and less uniformly stained by acridine orange than control cells from pure cultures. Addition of chloramphenicol to the mixed cultures, in quantities sufficient to kill the E. coli cells, abolished the increased sensitivity of C. albicans to amphotericin B or nystatin. In preliminary in vivo tests, E. coli did not sensitize C. albicans to the polyene antibiotics.

Amphotericin B↗

[Not Available].

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[Diminution of the antibacterial activity of antibiotics in cultures and in experimental mixed infections].

We have studied interactions between Staphylococcus aureus and Pseudomonas aeruginosa in the absence and the presence of four different antimicrobials in mixed cultures and experimental infections. These two bacterial species, in addition to having different properties, are known to be opportunistic pathogens often present in human microflora. Two main aspects have been investigated and they are related to modifications in two species affecting their equilibrium in the mixed bacterial population and also their pathogenicity markers. Our results indicate that 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 three cell wall inhibitors, pencillin G,D-cycloserine, and vancomycin, we have observed that 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 one of the antimicrobials was allowed to be in contact for 6 to 8 h with P. aeruginosa cells in a culture, we observed a decrease in their inhibitory effects against S. aureus. These results were supported by microscopical observation. It seems that the inhibitory effects of the antimicrobials have 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. Conversely, P. aeruginosa remained apparently unchanged through all these experiments. Our 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.

Animals↗