Effect of monensin on the invasiveness and multiplication of Legionella pneumophila.

The polyether antibiotic monensin exhibited bacteriostatic activity against a clinical isolate of Legionella pneumophila in vitro. Experiments designed to test the effect of the compound on the invasiveness and multiplication of L. pneumophila in HeLa cells showed that, in the presence of the antibiotic, legionellas that penetrated the cells did not multiply. However, monensin did not alter the characteristics of phagosomes that contained ingested legionellas. In the presence of monensin, infected cells exhibited extensive vacuolation and a noticeable reduction in the number of intracellular micro-organisms was evident a few hours after infection.