Increase in the in vitro susceptibility of Staphylococcus aureus to antimicrobial agents in the presence of Candida albicans

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Abstract
In mixed cultures of S. aureus and C. albicans in the absence and presence of 5-fluorocytosine (5-FC), there is an inhibition of S. aureus growth in mixed cultures with C. albicans in media supplemented with 1 .mu.g/ml of 5-FC and 5-FC has no effect on staphylococci in pure cultures. This inhibition occurred with clinically isolated and laboratory strains and could be reversed by specific metabolites. S. aureus was inhibited by filtrates of C. albicans cultures treated with 5-FC and this seemed favored by some C. albicans filterable product which can affect the cell wall and the permeability of the staphylococcal cells since they became sensitive to 5-FC. Nine other commonly used antimicrobials showed an increased inhibitory activity against S. aureus in mixed cultures with C. albicans: There is a decrease in the number of precipitating antigens of S. aureus and of the activity of .alpha.-toxin when this species was grown with C. albicans and 5-FC. The susceptibility of some species to antimicrobials may be significantly modified in the presence of other species. A similar phenomenon may occur in hosts under treatment with antibiotics against infection.