Chloromethyl-methylisothiazolone (CMIT/MIT) is a broad spectrum biocide which has been used successfully for microbial control and preventing biofouling in industrial water treatment. This paper presents a review of the various reports over the past 20 years on the efficacy of CMIT/MIT biocide versus Legionella bacteria and the protozoa associated with their growth. These studies included a wide range of conditions, including single organisms in cooling water and complex model systems with bacteria, biofilms, and protozoa. Overall, low levels of CMIT/MIT (1-10 ppm active) provided significant reduction in viable counts of various strains and species of Legionella bacteria in planktonic and biofilm studies and also against the amoebae and ciliated protozoa associated with their growth.
Bacteria which belong to the genus Legionella, are found in a range of aquatic environments, including tap water, cooling water and air conditioning systems, and are the causative agent of Legionellosis (Legionnaires' disease).1,2,3 The organisms were first identified following an outbreak at the 1976 American Legion Convention in Philadelphia, PA and have been the subject of numerous biocide efficacy studies.4 The type species and most frequently recognized member of the genus is Legionellapneumophila. Specific procedures using halogens to eradicate cooling towers containing high levels of Legionella are provided by ASHRAE (American Society of Heating Refrigerating and Air conditioning Engineers), AWT (Association of Water Technologies), and CTI (Cooling Technology Institute).1,2,3
This paper will provide a review of the factors involved in the growth and survival of Legionella bacteria in cooling water systems, their association with protozoa and biofilms, and the efficacy of isothiazolone biocide against these organisms.
Isothiazolone biocides are widely used for microbial control in industrial water treatment.5 The most frequently used product is a 3:1 ratio of 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and 2-methyl- 4-isothiazolin-3-one (MIT) at a final concentration of 1.5% total active ingredient.(1) CMIT/MIT has broad spectrum efficacy versus bacteria, algae, and fungi. The chemical structures of CMIT/MIT are shown in Figure 1. All biocide concentrations in this paper are reported on an active ingredient basis. The CMIT/MIT biocide described in this paper is manufactured by Rohm and Haas Company.
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Legionnaires' disease produces a flu-like lung infection (pneumonia) caused by a bacterium named Legionella pneumophila. To date, over 48 species of Legionella have been identified and >90% of the cases are linked to the species Legionella pneumophila. Approximately 5-15% of known Legionnaires' disease cases have been fatal, mostly in the elderly, sick, or individuals with suppressed immune systems. The route of exposure is considered to be by inhalation of aerosols (from sources such as cooling towers and showers), but recent studies have shown that building (potable) water distribution systems are considered as primary sources and that the route of infection is via "aspiration" of this water from the mouth into the lungs (not via aerosols directly) . Thus, the researchers at the University of Pittsburg Veterans Administration (VA) Hospital proposed that cooling towers are not considered the primary source for Legionella bacteria; potable water is.6 Additional info
