Heterotrophic Plate Count Can Predict the Presence of Legionella spp. in Cooling Towers

Author:

Sanchis Marta1234,Inza Isabel23,Figueras Maria José234

Affiliation:

1. Serra Húnter Fellow, Facultad de Medicina y Ciencias de la Salud, Departamento de Ciencias Médicas Básicas, Unidad de Microbiología y Microbiología Ambiental, Universidad Rovira i Virgili, 43003 Reus, Spain

2. Department of Basic Medical Sciences, University Rovira i Virgili, 43201 Reus, Spain

3. Pere Virgili Institute for Health Research (IISPV), 43204 Reus, Spain

4. University Institute for Research in Sustainability, Climate Change and Energy Transition (IU-RESCAT), 43480 Vila-seca, Spain

Abstract

Legionella pneumophila (Lp) colonizes aquatic environments and is a potential pathogen to humans, causing outbreaks of Legionnaire’s disease. It is mainly associated with contaminated cooling towers (CTs). Several regulations, including Spanish legislation (Sl), have introduced the analysis of heterotrophic plate count (HPC) bacteria and Legionella spp. (Lsp) in management plans to prevent and control Legionella outbreaks from CTs. The 2003 Sl for CTs (RD 865/2003) considered that concentrations of HPC bacteria ≤10,000 cfu/mL and of Lsp ≤100 cfu/L are safe; therefore, no action is required, whereas management actions should be implemented above these standards. We have investigated to what extent the proposed standard for HPC bacteria is useful to predict the presence of Lsp in cooling waters. For this, we analyzed Lsp and HPC concentrations, water temperature, and the levels of chlorine in 1376 water samples from 17 CTs. The results showed that in the 1138 water samples negative for Legionella spp. (LN), the HPC geometric mean was significantly lower (83 cfu/mL, p < 0.05) than in the positive Lsp. samples (135 cfu/mL). Of the 238 (17.3%) LP samples, 88.4% (210/238) were associated with values of HPC ≤10,000 cfu/mL and most of them showed HPC concentrations ≤100 (53.7%). In addition, a relatively low percentage of LP (28/238, 11.6%) samples were associated with HPC bacteria concentrations >10,000 cfu/mL, indicating that this standard does not predict the colonization risk for Legionella in the CTs studied. The present study has demonstrated that a threshold concentration ≤100 cfu/mL of HPC bacteria could better predict the higher concentration of Legionella in CTs, which will aid in preventing possible outbreaks.

Publisher

MDPI AG

Subject

Infectious Diseases,Microbiology (medical),General Immunology and Microbiology,Molecular Biology,Immunology and Allergy

Reference63 articles.

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