Factors influencing inactivation of Klebsiella pneumoniae by chlorine and chloramine

Inactivation of Klebsiella pneumoniae cultures by chlorine and chloramine was evaluated under different growth conditions by varying nutrient media dilution, concentrations of essential inorganic nutrients (FeCl3, MgSO4, phosphate, and ammonium salts), and temperature. All inactivation assays were performed at room temperature (22–23°C) and near neutral pH (7.2–7.5). C*T99.9 values for chlorine increased >20-fold and for chloramine increased 2.6-fold when cells were grown in 100-fold diluted nutrient broth (2NB) solutions (final TOC of 35–40 mg/L). Background levels of Mg: 6.75×10−2 mM and Fe: 3.58×10−5 mM or high levels of FeCl3 (0.01 mM) and MgSO4 (1 mM) during growth resulted in the highest resistances to chlorine with C*T99.9 values of 13.06 (±0.91) and 13.78 (±1.97) mg-min/L, respectively. Addition of low levels of FeCl3 (0.001 mM) and MgSO4 (0.1 mM) to K. pneumoniae cultures during growth resulted in the lowest bacterial resistances to inactivation; C*T99.9 values ranged from 0.28 (±0.06) to 1.88 (±0.53) mg-min/L in these cultures. Increase in growth temperature from 22.5°C to 35°C for unamended 2NB cultures resulted in a 42-fold decrease in C*T99.9 values for chlorine. A similar change in temperature resulted in no significant change in C*T99.9 values for chloramine. These results indicate that inactivation of K. pneumoniae cultures by chlorine was highly sensitive to changes in growth conditions unlike inactivation by chloramine.