Abstract: Mutated phosphotriesterase-like lactonases or functional fragments can be used in methods for treating or preventing infection of a bacterium in a host, such as a plant or a part, organ or a plant propagation material. The methods include applying the mutated phosphotriesterase-like lactonases or the wild-type enzyme to the host Cells expressing the mutated phosphotriesterase-like lactonases can also be produced using nucleic acid molecules and vectors encoding the mutated phosphotriesterase-like lactonases or functional fragments.