Effects of carbon sources on antibiotic resistance in Pseudomonas aeruginosa

The metabolism of branched-chain amino acids, branched-chain acyl derivatives, d-glucose, l-glutamate, and Mueller-Hinton medium was investigated to determine their effects on the growth, lipid composition, and antibiotic susceptibility of Pseudomonas aeruginosa. The unsaturated fatty acid content of the readily extractable lipids was altered by growth on selected branched-chain amino acids and their acyl derivatives. Bacteria grown on branched-chain acyl derivatives became more susceptible to polymyxin B and colistin. The effect acyl derivatives had on increasing susceptibility was also manifest in mixed media which contained both an acyl derivative and a carbon source which did not increase susceptibility. Growth on branched-chain amino acids gave mixed results which were dependent on a number of factors, including unique manifestations of individual amino acids, growth conditions, and availability of other carbon sources. The cultural conditions which altered susceptibility to polymyxin antibiotics did not correlate with similar effects on susceptibility to carbenicillin and gentamicin. An adaptive resistance to polymyxin B was observed when the sole carbon source was d-glucose or l-glutamate.