The Influence of the Type of Diluent on the Growth and Survival of Pseudomonas Putrefaciens1,2

Abstract

Summary Experiments using three pure cultures of Ps. putrefaciens showed that there was a wide variance among these cultures as to their ability to withstand the toxic effects of distilled water. Distilled water and redistilled (in glass) water rapidly inactivated the test organism. Less than 1.0 per cent of those originally present were viable after being suspended in these diluents for 1hr. Tap water showed a somewhat better compatibility with Ps. putrefaciens than distilled water. The data from trials with 0.9 per cent NaCl in distilled water (physiological saline) indicated that this diluent is reasonably compatible with Ps. putrefaciens for the first 0.5hr., but the test organism was rapidly inactivated upon being suspended in this saline solution for longer periods. The addition of 0.9 per cent NaCl to the gelatin-phosphate diluent slightly improved its compatibility with Ps. putrefaciens . The addition of 2.0 per cent NaCl caused a slight decrease in the survival indices of the test culture, and 4.0 per cent caused a definite decrease. The phosphate salts (0.725 per cent NaH 2 PO 4 + 0.37 per cent Na 2 HPO 4 ) are the component of gelatin-phosphate buffer solution contributing most to its excellent qualities as a diluent for Ps. putrefaciens . A 0.5 per cent phosphate solution was fairly satisfactory as a diluent for Ps. putrefaciens but was inferior to a 1.0 per cent solution. Similarly, a 1.0 per cent phosphate solution was inferior to a 2.0 per cent solution. When various concentrations of NaCl were added to reconstituted skimmilk, a general decrease in the survival of the test organism was noted as the percentage of added salt was increased. The sharpest decrease in the survival indices of the test culture occurred with 4 per cent as compared with 3 per cent added NaCl. Three methods of making the initial dilution of butter for plating were compared to determine which would yield maximum counts of Ps. putrefaciens . The method which yielded maximum counts in these studies is presented as a new procedure for making quantitative estimations and direct isolations of this organism from putrid butter.