A Strain of Pseudomonas aeruginosa Resistant to a Quaternary Ammonium Compound

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Abstract
Pseudomonas aeruginosa cells were selected for their ability to grow in the presence of 770 ppm n-alkyl (50% C12, 30% C14, 17% C16, 3% C18) dimethyl dichlorobenzyl ammonium chloride (QAC). These cells retained resistance to the germicide throughout tri-weekly transfers for 7 months in tryptone glucose yeast extract broth containing no QAC. Comparisons of resistant and sensitive cells were made in an attempt to define the mechanism of resistance and to provide some information as to the mode of action of QAC. Broth cultures of the resistant strain displayed a distinct fruity odor. Gas chromatographic analysis showed that the QAC-resistant cells, unlike the sensitive, produced large quantities of ethyl acetate and ethyl valerate. Two bands of esterase activity were demonstrated in sensitive cell extracts by gel electrophoresis, while only one band was detected in the resistant cell extracts when alpha napthyl acetate was used as the substrate. Biochemical tests disclosed numerous differences between the two cell types, many of which appeared to be interrelated. The most significant differences were losses in the ability of resistant cells to synthesize extracellular lipase and protease enzymes. Many other biochemical tests on resistant cells were negative or became positive only after prolonged incubation. Resistant cells were also more resistant to osmotic disruption. Permeability studies indicated a reduced rate of glucose uptake by resistant cells. Furthermore, growth curve studies indicated a slower rate of growth by resistant cells and a 15-min longer generation time.