Heterogeneity in chlorine susceptibility for Legionella pneumophila released from Acanthamoeba and Hartmannella

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To assess chlorine susceptibility of Legionella pneumophila grown from two amoebic hosts, Acanthamoeba castellanii and Hartmannella vermiformis.

Methods and Results

After being released from amoebae, Leg. pneumophila were chlorinated at 2 and 5 mg l−1 for 5 min–24 h. Bacterial culturability and cytoplasmic membrane deterioration were quantified by culture assay on BCYEα agar and BacLight stains coupled with a fluorescent microscope, respectively. Chlorination reduced the culturability of Leg. pneumophila by 2·93–4·59 log CFU ml−1 and damaged cellular membrane by 53·8–99·2%. Moreover, cells released from H. vermiformis exhibited significantly lower degrees in culturability reduction (P = 0·0008) and membrane deterioration (P < 0·0001) when compared with those from A. castellanii. The amoebic genus is the most significant parameter affecting cytoplasmic membrane integrity of chlorinated Legionella (P < 0·0001), followed by free chlorine concentration (P = 0·042).


Legionella pneumophila replicated from H. vermiformis possess greater chlorine resistance than the cells from A. castellanii.

Significance and Impact of the Study

This study shows the heterogeneity of amoebae-grown Leg. pneumophila in chlorine susceptibility, which should be considered in the control of legionellae proliferation, particularly in the systems where H. vermiformis is dominant, e.g. hot water plumbing.

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