Copper resistance inLegionella pneumophila: role of genetic factors and host cells

Abstract

AbstractCopper is frequently found in drinking water due to its presence in the natural environment and the widespread usage of copper pipes. This toxic metal has a well-known antimicrobial activity, an activity harnessed in copper-silver ionization (CSI) to eliminate the opportunistic pathogenLegionella pneumophilafrom engineered water systems. Despite utilizing the antimicrobial properties of copper inLegionellacontrol, little is known about how copper containing environments affectL. pneumophilapopulations. The goal of this study is to understand howL. pneumophilaresponds to copper within a hot water distribution system (HWDS) environment. To answer this question, different sequence types and regulatory mutants were exposed to copper to compare their survival.L. pneumophilaisolates of 4 sequence types from 3 different HWDSs exhibited a wide diversity of phenotypes after copper stress. The ΔletAand ΔletSmutants were sensitive to copper, indicating that the LetAS two component system is important for copper resistance. Additionaly, transmissive phase cultures were more resistant to copper than replicative phase cultures. Therefore, the regulation of entry into transmissive phase by the LetAS system is essential forL. pneumophila’s ability to survive copper stress. In a water system,L. pneumophilareplicates within eukaryotic hosts. When cocultured with the host ciliateTetrahymena pyriformis,L. pneumophilawas more resistant to copper than when the bacteria were in a monoculture. No difference inL. pneumophilareplication inside of hosts in cocultures with or without copper was observed. This result confirms that the presence of host cells protectsL. pneumophilafrom copper stress. Therefore, presence of host cells in water system may limit the efficacy of copper-based control strategies.