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Effect of pH of Solution on Germicidal Activity of Quaternary Ammonium Compounds¹

Oregon Agricultural Experiment Station, Corvallis

ABSTRACT

Comparative activity of four QACs against M. caseolyticus, E. coli and P. aeruginosa was determined at various pH levels ranging from pH 3 to 10.

M. caseolyticus showed great resistance to QAC action at levels below pH 6 to 7 and was rapidly destroyed in the alkaline range. E. coli was resistant at levels below pH 6, was highly susceptible at about pH 6 to 7, and then exhibited a second peak of high resistance at about pH 8.0. P. aeruginosa was most susceptible to QAC action at low pH levels and showed greatest resistance at pH 7 and above.

The variations in resistance of the different organisms, in general, were similar for the four QACs tested. This fact suggests that the marked variation in rate of destruction with alteration of pH is due to factors associated with the cell, rather than to specific effect of pH on activity of the QAC molecule as such.

¹ Published as Technical Paper no. 731 with the approval of the Director of the Oregon Agricultural Experiment Station. Contribution of the Department of Bacteriology.

² Present address: Dairy Dept., New Mexico State College.