Biopolymer Microparticles as a Potential Surrogate for Legionella Pneumophila

Sujani Ariyadasa, Beth Robson, Craig Billington, Liping Pang (ESR)

Gayan Abeysekera, Conan Fee (University of Canterbury)

Legionella pneumophila is an opportunistic pathogen in engineered water systems (EWS) that has led to numerous legionellosis outbreaks worldwide. They are often associated with pre-existing EWS biofilms as secondary colonizers, and their release to the bulk water phase upon biofilm maturation results in further contamination. Despite this known risk, the attachment and mobility of L. pneumophila in EWS biofilms has not been investigated in detail due to the biohazard and cost of detection. Improvement of legionellosis risk management in EWS requires routine investigations of L. pneumophila persistence in EWS using safe, representative, cost-effective, and easy-to-detect surrogates. The commonly used faecal indicator surrogate E. coli is a poor model for L. pneumophila due to their different properties. In this study, we developed a novel biopolymer surrogate with size, shape, surface charge, and hydrophobicity similar to
stationary phase L. pneumophila using polyelectrolyte-layered, DNA-encapsulated, alginate-calcium carbonate microparticles. We validated the surrogate’s ability to mimic L. pneumophila biofilm attachment/detachment kinetics using Pseudomonas fluorescens biofilms established on the surfaces of stainless-steel plumbing material in a laboratory-scale bioreactor under a continuous flow regime, in the absence and presence of chlorine.

The results of our preliminary validation studies showed that the surrogate produced similar attachment/detachment kinetics and magnitudes to/from biofilms as that of L. pneumophila in the bioreactor. The relative concentrations and peak attachment values for both entities were within the same orders of magnitude and their attachment processes were slower than detachment. Biofilm attachment of both the bacteria and surrogate were reduced in the presence of chlorine. In addition, P. fluorescens biofilm concentrations were not affected by exposure to the surrogate due to its biopolymer composition. These results show that with further, more robust validations under more EWS representative conditions, this novel surrogate may provide new insight into understanding L. pneumophila mobility and persistence in water systems.