Factors Involved in the Control of Microbial Deterioration: I. Variation in Sensitivity of Different Strains of the Same Species.

Numerous reports have appeared in the literature pertaining to laboratory studies of compounds that will inhibit microbial growth. The inhibitors that were found to be effective have been used in attempts to control microbial deterioration of various materials. These inhibitors have not functioned properly in some instances, and the investigators that reported these compounds to be effective have been blamed for such failures. It appears that the basic concepts pertaining to the intelligent use of inhibitors have been completely ignored. The variation in sensitivity to inhibitors of different strains of the same species is a factor of vital importance in the control of microbial deterioration. It is not sufficient to study the sensitivity of one stock culture to a particular compound but, instead, many strains should be examined and the concentration of the inhibitor must be sufficient to inhibit the most resistant strain that is likely to be encountered in the deterioration problem. The present investigation was undertaken to demonstrate the importance of this factor in the control of microbial deterioration. Phenols and nitroparaffin derivatives were selected because the variation in sensitivity of microorganisms to these compounds has not been studied extensively. Pseudomonas aeruginosa was selected as the test organism because it is involved in some deterioration problems and no variation in sensitivity studies using this organism could be found in the literature. Several experiments were performed in nutrient broth and, in addition, studies were carried out in metal cutting fluids in order to show that the phenomenon is not a laboratory oddity but is a basic factor in the preservation of any material from microbial attack.