Effectiveness of 1-bromo-3-chloro-5,5-dimethylhydantoin against Legionella pneumophila in a cooling tower

Legionella pneumophila Grows Adherent to Surfaces in vitro and in situ

Legionella pneumophila continues to play a role in both community- and nosocomially-acquired pneumonia. We investigated the ability of L pneumophila to adhere to various types of materials such as those found in the hospital air-cooling and potable water distribution systems. Through the use of a unique sampling apparatus, we were able to regularly acquire planktonic and sessile samples and determine the numbers of bacteria present in both populations, in vitro and in situ.

Portions of these apparatuses could be aseptically removed for examination by scanning electron microscopy, or for the determination of the number of viable adherent L pneumophila. The number of bacteria present in each sample was determined by direct plate count, with presumptive L pneumophila colonies being positively identified by direct fluorescent antibody staining techniques.

The results demonstrated that not only are legionellae capable of colonizing various metallic and nonmetallic surfaces but that they are preferentially found on surfaces. Surface-adherent bacteria may play a profound role as a reservoir of these potential pathogens in aquatic environments. Furthermore, these results suggest that any comprehensive legionella monitoring program must include not only water samples but also an examination of the adherent populations.

Ecology of Legionella: From Data to Knowledge with a Little Wisdom

The respiratory diseases produced by the Legionella genus of bacteria are collectively called Legionellosis. Presently more than 34 species of Legionella have been identified, 20 of which have been isolated from both environmental and clinical sources. The diseases produced by Legionella include the pneumonic form, Legionnaires' disease, and the flu-like form, Pontiac fever. Because the vast majority of Legionellosis is caused by the L. pneumophila species, this bacterium is the thrust of the discussion.Legionella is a global bacterium. The relationship of the bacterium to its environment has told us many things about infectious diseases. Not until Legionellosis and the discovery of its etiologic agent, Legionella, has such a successful modern-day marriage been consummated between the agent and its environment. Nearly two decades have passed since the term Legionellosis found its way into the vocabulary of the scientific journals, the popular press, and courtroom proceedings. Too often the scientific development, engineering implementation, and societal acceptance are disconnected. The focus of scientific research sometimes does not reflect engineering or societal needs and thus contributes little to the solution of immediate and important problems. At other times, scientific knowledge that could contribute to solutions is overlooked because of poor communication between the problem holders, the scientific community, regulatory agencies, the problem makers, and the public. The scope of this paper provides insights on the ecological niche of Legionella, describes the organism's ecological relationships in the natural world, and provides wisdom for effective control of the bacterium for the industrial and user communities.

Decreased biocide susceptibility of adherent Legionella pneumophila

In a study of the in vitro effectiveness of biocides against Legionella pneumophila, some aspects of the cooling tower environment were replicated in the laboratory, paying particular attention to water hardness and pH. Pieces of Douglas fir and polyvinyl chloride were colonized in a recirculating system and the comparative efficacy of two biocides (Bronopol and Kathon) against the sessile and planktonic populations was examined. While the biocides were relatively effective against the planktonic L. pneumophila population over a short period of time (minimum 9-12 h), substantially longer periods of time (maximum greater than 48 h) were required to reduce the number of cultivable bacteria to below detectable levels in the adherent population. The results indicate that failure to monitor the sessile population of L. pneumophila in laboratory studies of biocides may result in the use of incorrect dosages and/or contact times in field trials with apparently reduced in situ efficacy.

Effects of biocidal treatments to inhibit the growth of legionellae and other microorganisms in cooling towers

The effects of biocidal treatments for cooling towers were examined through the use of chemicals and ultraviolet irradiation to inhibit the growth of legionellae and other microorganisms. In the water of cooling towers without continuous biocidal treatments, heterotrophic bacteria and bacterivorous protozoan first appeared, and then legionellae increased up to 10(4) CFU/100 ml. When a UV sterilizer was connected to the cooling tower, the legionellae count was 1/10 or 1/100 of that in the nontreated tower water. In the water of towers supplemented continuously with the biocidal chemicals, legionellae were not found during a 4-month period. The biocidal treatments tested were proved to suppress the increase of legionellae in cooling-tower water, and thus are useful in preventing the outbreak of legionellosis due to inhalation of contaminated aerosol from the cooling tower system.

Legionella pneumophila grows adherent to surfaces in vitro and in situ

Legionella pneumophila continues to play a role in both community- and nosocomially-acquired pneumonia. We investigated the ability of L pneumophila to adhere to various types of materials such as those found in the hospital air-cooling and portable water distribution systems. Through the use of a unique sampling apparatus, we were able to regularly acquire planktonic and sessile samples and determine the numbers of bacteria present in both populations, in vitro and in situ. Portions of these apparatuses could be aseptically removed for examination by scanning electron microscopy, or for the determination of the number of viable adherent L pneumophila. The number of bacteria present in each sample was determined by direct plate count, with presumptive L pneumophila colonies being positively identified by direct fluorescent antibody staining techniques. The results demonstrated that not only are legionellae capable of colonizing various metallic and nonmetallic surfaces but that they are preferentially found on surfaces. Surface-adherent bacteria may play a profound role as a reservoir of these potential pathogens in aquatic environments. Furthermore, these results suggest that any comprehensive legionella monitoring program must include not only water samples but also an examination of the adherent populations.

Effects of three oxidizing biocides on Legionella pneumophila serogroup 1

A study was conducted to determine the bactericidal effects of ozone and hydrogen peroxide relative to that of free chlorine on Legionella pneumophila serogroup 1. In laboratory batch-type experiments, organisms seeded at various densities were exposed to different concentrations of these biocides in demand-free buffers. Bactericidal effects were measured by determining the ability of L. pneumophila to grow on buffered charcoal-yeast extract agar supplemented with alpha-ketoglutarate. Ozone was the most potent of the three biocides, with a greater than 99% kill of L. pneumophila occurring during a 5-min exposure to 0.10 to 0.30 micrograms of O3 per ml. The bactericidal action of O3 was not markedly affected by changes in pH or temperature. Concentrations of 0.30 and 0.40 micrograms of free chlorine per ml killed 99% of the L. pneumophila after 30- and 5-min exposures, respectively. A 30-min exposure to 1,000 micrograms of H2O2 per ml was required to effect a 99% reduction of the viable L. pneumophila population. However, no viable L. pneumophila could be detected after a 24-h exposure to 100 or 300 micrograms of H2O2 per ml. Attempts were made to correlate the biocidal effects of O3 and H2O2 with the oxidation of L. pneumophila fatty acids. These tests indicated that certain biocidal concentrations of O3 and H2O2 resulted in a loss or severe reduction of L. pneumophila unsaturated fatty acids.

Inactivation of Legionella pneumophila by hypochlorite and an organic chloramine

The susceptibility of a strain of Legionella pneumophila to disinfection by an organic halamine, free chlorine, and a mixture of the organic halamine and free chlorine was assessed. The organic halamine was found to have superior stability in solution and to exhibit adequate disinfectant potential over a period of 1 month of repeated reinoculations of fresh bacteria. The combined halamine exhibited great potential for use in maintaining closed-cycle cooling water systems free of L. pneumophila.

An alkaline approach to treating cooling towers for control of Legionella pneumophila

Earlier field and laboratory studies have shown that Legionella species survive and multiply in the pH range 5.5 to 9.2. Additionally, the technical feasibility of operating cooling towers at elevated alkalinities and pH has previously been documented by published guidelines. The guidelines indicate that these conditions facilitate corrosion control and favor chlorine persistence which enhances the effectiveness of continuous chlorination in biofouling control. This information suggests that control of Legionella species in cooling towers can be accomplished by operating the towers under alkaline conditions. To test this possibility, we collected water samples over a period of months from a hospital cooling tower. The samples were analyzed for a variety of chemical parameters. Subsamples were pasteurized and inoculated with non-agar-passaged Legionella pneumophila which had been maintained in tap water. Correlation of subsequent Legionella growth with corresponding pH and alkalinity values revealed statistically significant inverse associations. These data support the hypothesis that operating cooling towers outside of the optimal conditions for Legionella growth (e.g., at elevated alkalinities and a pH greater than 9) may be a useful approach to controlling growth in this habitat.