Research within Health & the Environment

Legionella: Ecology & Control
 - Comparison of the effectiveness of various biocidal treatments on Legionella contaminated biofilms

PhD Candidate: Michael Taylor
CIs: Richard Bentham

Legionella bacteria, the causative organisms of Legionnaires' disease, commonly colonize biofilms within the built environment. Preventative measures are routinely employed to disinfect and remove any biofilms capable of supporting their growth within these water systems. These measures include flushing super heated water through pipes, UV sterilization and chemical disinfection using bactericidal compounds such as chlorine (Kim et al. 2002). These treatments are not always ideal as heat treatment may not be logistically possible or chemical disinfection may pose an additional risk to human health. There exists a continuing research need to identify and evaluate new treatment regimes.

The effects of disinfectant treatments on planktonic bacterial populations are substantially different from those obtained with sessile bacterial populations contained within biofilms. The EPS excreted by the bacteria within the film has a protective effect as many active compounds and bactericidal chemicals are not able to reach the encapsulated bacteria (Szomolay et al. 2005). Current research is directed towards identifying compounds that are able to either remove and/or diffuse through the EPS in order to reach and disinfect the sessile bacteria contained upon surfaces.

To undertake reproducible trials of disinfectant treatments on biofilms containing Legionella, a laboratory scale biofilm reactor will be constructed. This reactor will be colonised with various bacteria derived from Legionnaires' disease outbreaks to form a model biofilm ecology. Biofilm will be grown on metal coupons which simulate the surfaces within water pipes. These coupons may then be treated with disinfectants and the bacterial populations analysed using a variety of techniques, paying particular attention to the Legionella and protozoan content within the films. A series of treatments will be evaluated and compared in order to establish the various efficacies of each under different conditions, such as varying the phosphate content of the water, water hardness and temperature.

References

  1. DONLAN, R. M. (2002) Biofilms: Microbial Life on Surfaces. Emerging Infectious Diseases, 8, 881-890.
  2. KIM, B. R., ANDERSON, J. E., MUELLER, S. A., GAINES, W. A. & KENDALL, A. M. (2002) Literature review--efficacy of various disinfectants against Legionella in water systems. Water Research, 36, 4433-4444.
  3. SZOMOLAY, B., KLAPPER, I., DOCKERY, J. & STEWART, P. S. (2005) Adaptive responses to antimicrobial agents in biofilms. Environmental Microbiology, 7, 1186-1191.
  4. XAVIER, J. B., PICIOREANU, C. & VAN LOOSDRECHT, M. C. M. (2004) A modelling study of the activity and structure of biofilms in biological reactors. Biofilms, 1, 377-391.