Vermamoeba vermiformis is a free-living amoeba (FLA) widely distributed in the environment, known to colonize hot water networks and to be the reservoir of pathogenic bacteria such as Legionella pneumophila. FLA are partly resistant to
biocides, especially in their
cyst form. The control of V. vermiformis in hot water networks represents an important health issue, but there are very few data on their resistance to disinfection treatments. The sensitivity of
cysts of two strains of V. vermiformis to three
disinfectants frequently used in hot water networks (
chlorine, heat shock,
peracetic acid (PAA) mixed with
hydrogen peroxide (H2O2)) was investigated. In vitro, several concentrations of
biocides, temperatures and exposure times according to the French regulation were tested.
Cysts were fully inactivated by the following conditions: 15 mg/L of
chlorine for 10 min; 60 °C for 30 min; and 0.5 g/L equivalent H2O2 of PAA mixed with H2O2 for 30 min. For the first time, the strong efficacy of
subtilisin (0.625 U/mL for 24 h), a
protease, to inactivate the V. vermiformis
cysts has been demonstrated. It suggests that novel approaches may be efficient for disinfection processes. Finally, V. vermifomis
cysts were sensitive to all the tested treatments and appeared to be more sensitive than Acanthamoeba
cysts.