Control of Legionella pneumophila by disinfectants. Effects of sodium hypochlorite against persistent strains

Legionella pneumophila is the causative agent of Legionnaires’ disease. Legionella is ubiquitous in natural freshwater ecosystems and it is frequently found in artificial aquatic systems. Due to its wide distribution and the impact on the human health, there have been applied many different physical and/or chemical treatments to control Legionella, especially in man-made water systems. We have reviewed the efficiency, advantages and limitations on chlorine and other disinfectants to control this important human pathogen. Besides, we have evaluated experimentally the effects of both, shock and continous treatments of chlorine (sodium hypochlorite) on viability and persistence of four different isolates of L. pneumophila sg1. We have demonstrated that both treatments were effective against Legionella pneumophila only when the bacteria were not previouly exposed to chlorine. We have also showed how under unfavourable environmental conditions such as disinfection treatments, some cells of populations might have differentiated to the viable non culturable stage. These findings should be considered in order to design effective methodologies to detect and prevent the presence of L. pneumophila in diverse natural and artificial aquatic habitats.