RESUMO
1. Possible interference of a nutritional solution (Vamin) with the activity of several aminoglycosides against Pseudomonas aeruginosa was evaluated in vitro. 2. Inactivation in cultures of 0.75, 1.2, 2.8, 65 micrograms/ml of gentamicin, kanamycin, amikacin, streptomycin, and tobramycin was induced by the addition of 1:20 v/v of the nutritional solution. 3. This inactivation was due to the presence of specific amino acids in the mixture. Deletions of amino acids from the media and amino acid analysis of the cellular pool revealed that valine, leucine, isoleucine, tyrosine, tryptophan, phenylalanine, cysteine, methionine, or threonine were responsible for the inactivation. 4. The concentration of threonine decreased in kanamycin and amikacin treated cells suggesting that certain aminoglycoside antibiotics undergo a decrease in activity when sensitive Ps. aeruginosa are treated with a nutrient solution. 5. Specific amino acids may interfere with the activity of antibiotics by circumventing their effect on amino acid biosynthesis.
