A Strain of Pseudomonas aeruginosa Resistant to a Quaternary Ammonium Compound

Abstract

Cells of Pseudomonas aeruginosa able to grow in Tryptone glucose yeast extract (TGY) broth containing 750 μg/ml of quaternary ammonium compound (alkyldimethylethylbenzyl ammonium chloride-(QAC) were studied in comparison to sensitive cells unable to grow in such medium to identify factors important in determining the precise degree of resistance. The germicidal activity of QAC solutions against both sensitive and resistant cells in TGY broth was shown to be greatly affected by the concentration of Tryptone and yeast extract, but not by the amount of sugar. The pH of the broth also influenced germicidal activity; both strains were more susceptible under slightly acid conditions. A comparison of the pH range of growth of sensitive and resistant cells demonstrated the abiility of the former to grow in TGY broth at pH 4.5 while the latter could not achieve growth at pH 5.0. A study of the effects of 50 ppm QAC, buffered to various pH values, indicated that susceptibility of resistant cells was nearly the same as that of sensitive cells below pH 3.0, at pH 6.0, and above pH 9.0. The greatest difference between the two cell types occurred from pH 3.5 to pH 4.5 with a second peak of resistance being observed from pH 7.0 to pH 8.5.