Impact of growth conditions on resistance of Klebsiella pneumoniae to chloramines

Abstract

The resistance of Klebsiella pneumoniae to inorganic monochloramine (1.5 mg/liter; 3:1 Cl2:N ratio, pH 8.0) was examined in relation to growth phase, temperature of growth, and growth under decreased nutrient conditions. Growth phase did not impact resistance to chloramines. Mid-exponential and stationary-phase cells, grown in a yeast extract-based medium, had CT99 values and standard deviations of 4.8 ± 0.1 and 4.6 ± 0.2 mg · min/liter, respectively. Growth temperature did not alter chloramine resistance at short contact times. CT99 values of cells grown at 15 and 23°C were 4.5 ± 0.2 and 4.6 ± 0.2 mg · min/liter, respectively. However, at longer contact times, CT99.99 values of cells grown at 15 and 23°C were 14 and 8 mg · min/liter, respectively, suggesting a small resistant subpopulation for cells grown at the lower temperature. Growth under decreased nutrient conditions resulted in a concomitant increase in resistance to chloramines. When K. pneumoniae was grown in undiluted Ristroph medium and Ristroph medium diluted by 1:100 and 1:1,000, the CT99 values were 4.6 ± 0.2, 9.6 ± 0.4, and 24 ± 7.0 mg · min/liter, respectively. These results indicate that nutrient availability has a greater impact than growth phase or growth temperature in promoting the resistance of K. pneumoniae to inorganic monochloramine.