Samples obtained from plumbing systems of hospitals, nonhospital institutions, and homes were cultured for Legionella spp. by plating the samples directly on a selective medium. Swab samples were taken from the inner surfaces of faucet assemblies (aerators, spouts, and valve seats), showerheads, and shower pipes. Water and sediment were collected from the bottom of hot-water tanks. Legionella pneumophila serogroups 1, 5, and 6 were recovered from plumbing fixtures of the hospitals and nonhospital institutions and one of five homes. The legionellae (7 to 13,850 colony-forming units per ml) were also present in water and sediment from hot-water tanks maintained at 30 to 54°C, but not in those maintained at 71 and 77°C. Legionella micdadei was isolated from one tank. Thus legionellae are present in hot-water tanks which are maintained at warm temperatures or whose design results in warm temperatures at the bottom of the tanks. We hypothesize that hot-water tanks are a breeding site and a major source of L. pneumophila for the contamination of plumbing systems. The existence of these bacteria in the plumbing systems and tanks was not necessarily associated with disease. The extent of the hazard of this contamination needs to be delineated.

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.

No abstract

Naturally occurring Legionella pneumophila, an environmental isolate which had not been grown on artificial medium, was tested for the ability to multiply in tap water. A showerhead containing L. pneumophila and non-Legionellaceae bacteria was immersed in nonsterile tap water supplying this fixture. Also L. pneumophila and non-Legionellaceae bacteria were sedimented from tap water from a surgical intensive care unit. This bacterial suspension was inoculated into tap water from our laboratory. The legionellae in both suspensions multiplied in the tap water at 32, 37, and 42°C. The non-Legionellaceae bacteria multiplied at 25, 32, and 37°C. A water sample which was collected from the bottom of a hot water tank was found to contain L. pneumophila and non-Legionellaceae bacteria. These legionellae also multiplied when the water sample was incubated at 37°C. These results indicate that L. pneumophila may multiply in warm water environments such as hot water plumbing fixtures, hot water tanks, and cooling towers. Water and moist environments may be the natural habitats for Legionella pneumophila. These bacteria have been isolated from natural waters such as lakes, ponds, and streams (4, 5, 11), from cooling towers of air conditioning systems (8), and from the plumbing systems of hospitals and hotels (2, 15). Tison et al. (14) have reported growth of L. pneumophila with a mean doubling time of 2.7 h in coculture with cyanobacteria under conditions of illumination. Only slight growth of the legionellae occurred when photosynthesis was inhibited by either dark incubation or exposure to a chemical inhibitor of photosystem II. These investigators concluded that the high rate of multiplication of L. pneumophila was dependent on active photosynthesis of the cyanobacteria. Accordingly, under conditions of darkness, which occur in plumbing systems, the cyanobacteria may not be able to support the growth of L. pneumophila. Factors other than cyanobacterial photosynthesis may be involved in providing the nutrients for the growth of the legionellae in tap water in plumbing systems. The work of Highsmith et al. (Abstr. Annu. Meet. Am. Soc. Microbiol. 1979, Q71, p. 231) suggests that L. pneumophila may be able to grow in sterile water that is used for intravenous injection. These investigators found that, after incubation for 6 weeks at 25°C after inoculation with L. pneumophila, bottles of the water became turbid. Examination by Gram staining, phase-contrast microscopy, and direct immunofluores