Effects of Japan Sea Proper Water on the Growth of \it{Legionella pneumophila

ABSTRACT

Objective: To assess whether Legionella pneumophila serogroup 1 and serogroup 6, Escherichia coli, and Staphylococcus aureus can survive in Japan Sea Proper Water (JSPW). Methods: The inhibitory effects of JSPW, surface seawater (SSW), phosphate buffer solution with 3.5% NaCl of pH 7.0 (3.5%NaClPBS), and the 102- and 104-fold dilute solutions with purified water or phosphate buffer solution of pH 7.0, and purified water were investigated. Survival cells were counted immediately after the water and the bacteria were mixed, and at 1, 3, 5, and 7 days after incubation at 37°C. If the number of surviving cells was decreased more than 2 log units compared with the starting value, we judged the medium to have had an inhibitory effect on the growth of the bacteria. Results: The survival cells of the bacteria in JSPW had decreased more than 2 log units compared with the starting value at 1 day after incubation. After 1 day of incubation, the cells of Legionella pneumophila serogroup 6 and Staphylococcus aureus were found to have decreased more than 2 log units in purified water (PW) used as a control. Furthermore, Legionella pneumophila serogroup 1 in the 102-fold dilute solution of JSPW was only 1.04 log units lower than the starting value at 7 days after incubation. In the 102- and 104-fold dilute solutions of JSPW, Escherichia coli survived for 7 days after incubation. These results were almost similar to the results in SSW and 3.5%NaClPBS. Conclusions: The present findings demonstrate that Legionella pneumophila serogroup 1 and Escherichia coli cannot survive in undiluted JSPW for over a day at 37°C, suggesting the inhibitory effects may be due to the sodium chloride contained in JSPW.