Malka Halpern

Malka Halpern

University of Haifa, Israel

Title: Leginella ecology in drinking water distribution


Prof. Malka Halpern is is an Environmental Microbiologist at the University of Haifa. She has completed her PhD from Haifa University, Israel and her postdoctoral studies from Tel-Aviv University, Israel. Her main interests are the ecology of waterborne pathogens and in particular Vibrio cholerae, Aeromonas and Legionella, Plant-bacteria interactions and Bacterial taxonomy. She has published more than 49 papers in reputed journals.


Bacteria of the genus Legionella cause water-based infections, resulting in severe pneumonia. Our aim was to improve our knowledge regarding Legionella ecology in drinking water systemes in Israel. Seasonal samples were taken from water and biofilm at seven sampling points of a small drinking water distribution system. Legionella pneumophila (Lp) was isolated and identified to its genotype level. High resolution genotyping of Lp isolates was achieved by Multiple-Locus Variable number of tandem repeat Analysis (MLVA). Within the studied water system, Legionella plate counts were significantly higher in summer. Legionella was isolated from six out of the seven selected sampling points, with counts up to 5.8*103 cfu/l. Lp counts were negatively correlated with chlorine. Five Lp MLVA-genotypes (Gt4, GT6, GT15, GT17 and GT48) were identified at different buildings along the water systeme route. The presence of a specific genotype, GT4, consistently co-occurred with high Legionella counts and seemed to “trigger” high Legionella counts in cold water. In laboratory experiments GT4 isolates exhibited superior growth abilities at 37°C-42°C, with shorter lag-phase (λ), higher growth rates (µm) and maximal cell densities (A), compared to 25°C-30°C, and also compared to genotypes GT6 and GT15 at the same tempertaures. GT4 strains were observed as causative agents of Legionnaire's disease. Our hypothesis is that the presence of specific genotypes, may indicate high Legionella concentration in water and that adaptation for growth at human body temperatures may assist some Lp strains to successfully infect and proliferate within the human body, thus facilitating their ability to cause illness.