Isolation and identification of a self-growth-inhibiting substance produced by Legionella sp. and its application as an anti-Legionella drug

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Legionella species, ubiquitous Gram-negative bacteria, are found in natural or man-made water systems. Their natural hosts are probably various amoebae species. If humans inhale aerosolized water from sources contaminated with them, such as cooling towers or whirlpool spas, the bacteria can invade and replicate within alveolar macrophages, causing a severe form of pneumonia called Legionnaires' disease. If the pneumonia is not treated promptly with antibiotics effective against the bacterium, the mortality rate can approach 15-20%. Therefore, control and management of Legionella contamination in some water systems are very important. Activated charcoal is usually added to a medium for the culture of Legionella species to enhance the growth of the bacteria. We found that activated charcoal can be replaced by Diaion HP-20 resin and that methanol extracts of the resins recovered from the culture broth of Legionella pneumophila showed strong growth-inhibitory activity toward the bacterium itself. The growth inhibitor was isolated from the methanol extracts and identified as sulfur. Sulfur was not obtained from the resins in a medium without cultivation of the bacterium, indicating that it was produced endogenously by the bacterium. Sulfur shows strong growth-inhibitory activity toward all Legionella species tested. Our results obtained in this study showed that sulfur may be a good candidate as a drug for preventing Legionella contamination in water systems effectively and cheaply.