Water characteristics associated with the occurrence of Legionella pneumophila in dental units

This study evaluated the incidence of Legionella pneumophila in dental unit water samples and investigated how the occurrence of these bacteria may be related to some physical? chemical and bacteriological characteristics of the water, The samples were taken from the incoming tap water. oral rinsing cup, air-water syringe: ultrasonic scaler, and the turbine of 23 dental un its of private and public institutions. Apart from L. pneumophila (serogrou p 1 and 3) isolated in 22 out of the 101 (21.8%) water samples tested, two other species were found: L. bozemanii and L. dumoffii. The highest densiti es and frequency of L. pneumophila were observed in the water coming into t he units and in the dental units of public institutions. A negative associa tion between L. pneumophila and 36 degrees C and 22 degrees C heterotrophic total plate counts and other Gram-negative bacteria was found. An inverse association between the concentration oft. pneumophila and water temperatur e was also observed. The values of pH and total hardness did not show any s ignificant difference in the L. pneumophila-positive and -negative dental u nit waters. Finally. the chemical oxygen demand (COD) and residual chlorine were found to correlate positively with L. pneumophila.