Attenuated Legionella pneumophila Survives for a Long Period in an Environmental Water Site
Figure 3
Resistance of environmental strains from Ashiyu foot spa 2 against stress factors. (a) Each strain was incubated for 6 h at 37°C with or without 2 mM hydrogen peroxide (H2O2). CFU counts were determined using serial dilution on BCYE. The relative increase was calculated by dividing the CFU of culture with H2O2 by the CFU of culture without H2O2. (b) Each strain was exposed to 0.1 ppm chlorine (Cl2) at room temperature for 1 min and 3 min. After neutralization, CFU counts were determined using serial dilution on BCYE. The percentage of culturable bacteria was calculated by dividing the CFU of treated bacteria by the CFU of untreated bacteria (n.d.: not detected). (c) Each strain was heat-treated for 30 min at 55°C. CFU counts were determined using serial dilution on BCYE. The percentage of culturable bacteria was calculated by dividing the CFU of treated bacteria by the CFU of untreated bacteria. (d) Each strain was suspended by 0.2 M HCl-KCl buffer (pH2.2) and incubated for 6 h at room temperature. CFU counts were determined using serial dilution on BCYE. The percentage of culturable bacteria was calculated by dividing the CFU of treated bacteria by the CFU of untreated bacteria. All values represent the average and the standard deviation for three identical experiments. Statistically significant differences compared with Togus-1 are indicated by asterisks (, P < 0.05, and , P < 0.01).