The effect of drying, heat, and pH on the survival of Legionella pneumophila.

The susceptibility of Legionella pneumophila, Philadelphia 1 strain, to drying, pH variation, and heating was determined and compared to that of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. L. pneumophila was quite sensitive to drying, with a four log drop in viability occurring during the first 30 seconds. After 90 minutes of drying in tap water, some samples contained no viable organisms, whereas E. coli, S. aureus, and P. aeruginosa still contained several thousand viable organisms. L. pneumophila showed a two log drop in viable cells after being held for one month in tap water varying in pH from 4 to 7. This was similar to what was found for P. aeruginosa. However, at pH 8 there was a six log drop in viability for L. pneumophila which was not evident with P. aeruginosa. At pH 2 to 3, both organisms could only survive short term (minutes) exposure. Heating experiments revealed a four log drop in viability for L. pneumophila at temperatures ranging from 55 to 65 degrees C. The survival of E. coli and S. aureus was greater at these temperatures.