Effect of temperature, pH, and oxygen level on the multiplication of naturally occurring Legionella pneumophila in potable water

Abstract

A water culture containing naturally occurring Legionella pneumophila and associated microbiota was maintained in the laboratory by serially transferring the culture in tap water which had been sterilized by membrane filtration. Successful maintenance of the water culture depended upon transferring the culture when the growth of L. pneumophila was in the late-exponential to early-stationary phase. The water culture was used as a source of naturally occurring bacteria to determine some of the parameters which affect the multiplication of L. pneumophila in tap water. Naturally occurring L. pneumophila multiplied at a temperature between 25 and 37°C, at pH levels of 5.5 to 9.2, and at concentrations of dissolved oxygen of 6.0 to 6.7 mg/liter. Multiplication did not occur in tap water which contained less than 2.2 mg of dissolved oxygen per liter. An association was observed between the multiplication of L. pneumophila and the non-Legionellaceae bacteria which were also present in the water culture. The method of preserving naturally occurring L. pneumophila and associated microbiota may facilitate studies on the symbiosis of L. pneumophila with other microorganisms.

Micro- and macromethod assays for the ecological study ofLegionella pneumophila

“…Legionella have never been detected in the same assays performed at 48°C, underlining that in our experimental conditions this temperature was too high for legionellae survival, as reported by other authors in experiments carried out in filter-sterilized waters [27,29,30]. Nonetheless, as legionella is detected in hot water systems [31], even at high temperatures, we must note that our artificial microcosms do not represent the real environment but give useful indications on the capability of Lp-1 to survive under definite and con-trolled experimental conditions.…”

“…Lee and West [33] report that L. pneumophila suspended in sterilized tap or distilled water at 25°C, after initial fluctuations, may survive for long periods, up to 65 days, stabilizing at a level slightly above that initial concentration. Moreover, several groups, which performed the test by removing and replacing the microcosms with fresh sterile tap water at regular intervals, showed that L. pneumophila cultured at 35°C remained indefinitely without the addition of any nutrient other than those occurring naturally in the water [30,34].…”

Stationary phase and mature infectious forms of Legionella pneumophila produce distinct viable but non‐culturable cells

“…up to 14 months in tap water with only a modest loss in culturability in the first few months (Skaliy and McEachern, 1979;Schofield, 1985). However, at high temperatures well above its ∼37°C growth optimal (Yee and Wadowsky, 1982;Wadowsky et al, 1985;Kusnetsov et al, 1996), the loss of culturability and viability in starved L. pneumophila is accelerated (Ohno et al, 2003). At 50°C, culturability dropped from 100% to 25% in 60 min (Groothuis and Veenendaal, 1983), and at >50°C, a clear loss of viability was observed after 40 min (Fliermans et al, 1981a).…”

Contamination of domestic water heaters with Legionella pneumophila: Impact of water temperature on growth and dissemination of the bacterium

“…These findings suggest that temperature around 30°C may be optimal for the multiplication of L. pneumophila. Wadowsky has indeed shown previously that multiplication of L. pneumophila occurred between temperatures of 25-37°C whereas at temperatures above 42"C, the actual number of L. pneumophila declined rapidly (Wadowsky et al, 1985a). Finally, the dissemination of legionella occurred only when the outlet water temperature was below 56°C.…”