Effect of salt concentration and temperature on survival of Legionella pneumophila

The effects of various concentrations of sodium chloride solutions (0.1%-3%) and different temperatures (4, 10, 20, 30 and 37 degrees C) on survival of Legionella pneumophila were investigated. It was found that at temperatures between 4 degrees C and 20 degrees C, Legionella organisms survived in salt solutions up to 3% NaCl. Only the combination of high temperatures, i.e. 30 degrees C and 37 degrees C, with NaCl concentrations over 1.5%, reduced cell numbers significantly. It was interesting to note that the addition of small amounts of NaCl (0.1%-0.5%) enhanced survival of Leg. pneumophila, suggesting a protective effect of NaCl. In order to obtain information about conditions encountered in the environment, the survival experiments were repeated in sterile sea water from the Baltic Sea and the North Sea. The marked bacterial die-off, especially at higher temperatures, was not observed in natural sea water. All these results indicate that Leg. pneumophila can survive in the marine environment.