Abstract
Legionella pneumophila (Lp) is the etiological agent responsible for Legionnaires’ disease, a potentially fatal pulmonary infection. Lp lives and multiplies inside protozoa in a variety of natural and man-made water systems prior to human infection. Fraquil, a defined freshwater medium, was used as a highly reproducible medium to study the behaviour of Lp in water. Adopting a reductionist approach, Fraquil was used to study the impact of temperature, pH and trace metal levels on the survival and subsequent intracellular multiplication of Lp in Acanthamoeba castellanii, a freshwater protozoan and a natural host of Legionella. We show that temperature has a significant impact on the short- and long-term survival of Lp, but that the bacterium retains intracellular multiplication potential for over six months in Fraquil. Moreover, incubation in Fraquil at pH 4.0 resulted in a rapid decline in colony forming units, but was not detrimental to intracellular multiplication. In contrast, variations in trace metal concentrations had no impact on either survival or intracellular multiplication in amoeba. Our data show that Lp is a resilient bacterium in the water environment, remaining infectious to host cells after six months under the nutrient-deprived conditions of Fraquil.
Highlights
Identified as the etiological agent of Legionnaires’ disease in the late 1970’s, Legionella pneumophila (Lp) is a Gram-negative, water-borne bacterium [1]
We tested the survival of Lp in Fraquil, hereafter called water, exposed to six different temperatures ranging from refrigeration to the high end of the temperature spectrum recorded as supporting Legionella growth [40]: 4°C, 10°C, 25°C, 30°C, 37°C and 42°C
Our results show that even moderate temperatures between 30°C to 42°C significantly impact the survivability of Lp in a minimal water system (Fig 1A)
Summary
Identified as the etiological agent of Legionnaires’ disease in the late 1970’s, Legionella pneumophila (Lp) is a Gram-negative, water-borne bacterium [1]. Inhalation of Legionella-contaminated aerosols can lead to Legionellosis, which is comprised of the mild, flu-like Pontiac fever and the more serious pneumonia, Legionnaires’ disease [2, 3]. Legionella species are often found in freshwater bodies as well as an assortment of man-made water distribution systems [4,5,6,7] with the exception of Legionella longbeachae whose presence in potting soils is linked to the incidence of Legionnaires’ disease in Australia and New Zealand [8]. Public health concerns related to Lp are mainly associated with its contamination of cooling towers and other man-made water distribution systems [10].
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