Survial of Legionella pneumophila in a Model Hot Water Distribution System

Abstract

A virulent strain of Legionella pneumophila was inoculated into an enclosed system supplied with unsterilized water from a domestic hot water supply. Growth of bacteria was monitored over 10 weeks. An increase in the number of organisms other than legionellas occurred but few amoebae were observed and none could be cultured. Viable counts of L. pneumophila in the circulation fluid decreased slightly. However, particles of debris which accumulated in the apparatus and which were stained by the indirect fluorescent antibody technique were found to be almost totally composed of L. pneumophila. On dismantling the apparatus Legionella was isolated in moderately high numbers from several different types of surfaces, particularly natural rubber and silicone.

The persistence of Legionella pneumophila in non‐sterile, sterile and artificial hard waters and their growth pattern on tap washer fittings

“…Filamentous cells were also observed using SEM ( Fig. 7) and were generally similar in appearance to the majority of nonlegionella organisms cultivated from the tap water and seen in previous samples (Schofield & Wright 1984;Schofield 1985).…”

“…These consisted of: stainless steel squares, copper and aluminium discs (Schofield & Wright 1984); a synthetic 'rubber' neoprene tap washer Dexing BSS 1010 518'' and a natural rubber tap washer 5/8" (London & Lancashire Rubber Company Ltd); a large synthetic 'rubber' '0' ring and plastic '0' ring (McAlpine Ltd), and a zinc plated mild steel washer (Welpac Ltd). All washers were purchased from a plumbers merchant (Woodrows, Salisbury).…”

“…Organisms other than legionellas were also present and a complex colonization matt was formed which was embedded in a protective coat of slime and debris. The numbers of L. pneumophila recovered from the water were highest between 4 and 7 weeks but they could still be cultivated after 4 months An investigation of a model hot water system seeded with a virulent strain of Legionella pneumophila serogroup 1 showed that the cells were able to survive in mains tap water (Schofield & Wright 1984). Ten weeks after inoculation the water and materials of the model hot water system were sampled for the presence of L. pneumophila.…”

Legionnaires’ disease

“…Bacterial counts taken from bulk water samples do not reflect the number of bacteria present in the system (ref. 10). Surfaces are now believed to play an important role in the speed of recolonization of systems once they have been nominally disinfected.…”

“…Very small bubbles of 0.3 mm diameter have no film drops. Bubbles of 1.7 mm diameter produce from 10 to 20 film droplets, with half of them being smaller than 10 …”