Factors Stimulating Propagation of Legionellae in Cooling Tower Water

Abstract

Our survey of cooling tower water demonstrated that the highest density of legionellae, 104 CFU/100 ml, appeared in water containing protozoa, >102 MPN/100 ml, and heterotrophic bacteria, >10' CFU/100 ml, at water temperatures between 25 and 35°C. Viable counts of legionellae were detected even in the winter samples, and propagation, up to 10S CFU/100 ml, occurs in summer. The counts of legionellae correlated positively with increases in water temperature, pH, and protozoan counts, but not with heterotrophic bacterial counts. The water temperature of cooling towers may promote increases in the viable counts of legionellae, and certain microbes, e.g., protozoa or some heterotrophic bacteria, may be a factor stimulating the propagation of legionellae.

Comparison of Detection Methods for Legionella Species in Environmental Water by Colony Isolation, Fluorescent Antibody Staining, and Polymerase Chain Reaction

“…Survey and monitoring of legionellae in environments are needed to prevent and control legionellosis. Legionella species are recovered from aquatic environments, such as rivers (18), lakes and ponds (8), cooling towers (13,21), and even tapwater (15). In water samples from these environments, cell numbers of legionellae were 102 to 105 cell/ml by direct counting with fluorescent antibody (FA) staining (8,18).…”

“…In water samples from these environments, cell numbers of legionellae were 102 to 105 cell/ml by direct counting with fluorescent antibody (FA) staining (8,18). On the other hand, colony numbers of legionellae from the water samples were usually lower than the number detected by direct counting (18,21). Several surveys also reported that legionellae were not isolated from many FA-positive samples, cooling tower water (13), tap-water (15), or river water (18).…”

“…Viable count and direct count of legionellae. Colony count of legionellae in the samples was carried out by the procedure previously described (20,21).…”

“…The LP primers specificity for L. pneumophila was tested using the type strains of 29 Legionella species, prior to using for the survey (data not shown). LEG primers (LEG448-A, 5'-GAG GGT TGA TAG GTT AAG AGC-3'; LEG854-B, 5'-CGG TCA ACT TAT CGC GTT TGC T-3') were designed from the partial sequences of 16S ribosomal RNA of Legionella species (9 As shown in Table 2, the temperature and pH of cooling tower water showed typical ranges during operation in summer (20,21). Total bacterial counts were 106 to 108 cell/100 ml of water samples from the cooling towers, and 107 ce11/100 ml of river water.…”

Detection and occurrence of waterborne bacterial and viral pathogens

“…) (Martinez-Manzanares et al) (Doyle et al; Leung et al; Martinez-Manzanares et al; O'Shea and Field; Stelzer and Jacob; Stelzer et al; Townsend) (Carmichael; Harding; Li, W. K. W. et a/.) (O'Shea and Field; Townsend) (Barrell; Gauthier et al; Martinez-Manzanares et al; Prabu and Mahadevan, Rice et al; Shadix and Rice, 1991; Townsend) (West et al) (Lye and Dufour, 1991; Martinez-Manzanares et al; Yamamoto et al)(Cargill et al;Paszko-Kolva et a/., 1991;Sanden et al;Yamamoto, H. et al) (Gennari and Dragotto; Leung et a/. ; O'Shea and Field) (Martinez-Manzanares et al; O'Shea and Field; Townsend) (Martinez-Manzanares et al; O'Shea and Field; Stelz and Zschock) (Martinez-Manzanares et al; O'Neill et al; Vanoy et al)…”