Dataset Information

Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain.

ABSTRACT: Following nosocomial cases of Legionella pneumophila, the investigation of a hot water system revealed that 81.5% of sampled taps were positive for L. pneumophila, despite the presence of protective levels of copper in the water. A significant reduction of L. pneumophila counts was observed by culture after heat shock disinfection. The following corrective measures were implemented to control L. pneumophila: increasing the hot water temperature (55 to 60 °C), flushing taps weekly with hot water, removing excess lengths of piping and maintaining a water temperature of 55 °C throughout the system. A gradual reduction in L. pneumophila counts was observed using the culture method and qPCR in the 18 months after implementation of the corrective measures. However, low level contamination was retained in areas with hydraulic deficiencies, highlighting the importance of maintaining a good thermal regime at all points within the system to control the population of L. pneumophila.

SUBMITTER: Bedard E

PROVIDER: S-EPMC4931386 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain.

Bédard Emilie E Boppe Inès I Kouamé Serge S Martin Philippe P Pinsonneault Linda L Valiquette Louis L Racine Jules J Prévost Michèle M

Pathogens (Basel, Switzerland) 20160415 2

Following nosocomial cases of Legionella pneumophila, the investigation of a hot water system revealed that 81.5% of sampled taps were positive for L. pneumophila, despite the presence of protective levels of copper in the water. A significant reduction of L. pneumophila counts was observed by culture after heat shock disinfection. The following corrective measures were implemented to control L. pneumophila: increasing the hot water temperature (55 to 60 °C), flushing taps weekly with hot water, ...[more]

PMID: 27092528

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Project description:BACKGROUND:Heat shock is a potential control strategy for Legionella pneumophila in hot water plumbing systems. However, it is not consistently effective, with little understanding of its influence on the broader plumbing microbiome. Here, we employed a lab-scale recirculating hot water plumbing rig to compare the pre- and post-"heat shock" (i.e., 40???60???40 °C) microbiota at distal taps. In addition, we used a second plumbing rig to represent a well-managed system at 60 °C and conducted a "control" sampling at 60 °C, subsequently reducing the temperature to 40 °C to observe the effects on Legionella and the microbiota under a simulated "thermal disruption" scenario. RESULTS:According to 16S rRNA gene amplicon sequencing, in the heat shock scenario, there was no significant difference or statistically significant, but small, difference in the microbial community composition at the distal taps pre- versus post-heat shock (both biofilm and water; weighted and unweighted UniFrac distance matrices). While heat shock did lead to decreased total bacteria numbers at distal taps, it did not measurably alter the richness or evenness of the microbiota. Quantitative PCR measurements demonstrated that L. pneumophila relative abundance at distal taps also was not significantly different at 2-month post-heat shock relative to the pre-heat shock condition, while relative abundance of Vermamoeba vermiformis, a known Legionella host, did increase. In the thermal disruption scenario, relative abundance of planktonic L. pneumophila (quantitative PCR data) increased to levels comparable to those observed in the heat shock scenario within 2 months of switching long-term operation at 60 to 40 °C. Overall, water use frequency and water heater temperature set point exhibited a stronger effect than one-time heat shock on the microbial composition and Legionella levels at distal taps. CONCLUSIONS:While heat shock may be effective for instantaneous Legionella control and reduction in total bacteria numbers, water heater temperature set point and water use frequency are more promising factors for long-term Legionella and microbial community control, illustrating the importance of maintaining consistent elevated temperatures in the system relative to short-term heat shock.

Project description:BACKGROUND:Legionella pneumophila, the causative agent of Legionnaire's disease, may enter a viable but non-culturable (VBNC) state triggered by environmental stress conditions. Specific outer-membrane epitopes of L. pneumophila are used in many diagnostic applications and some of them are linked to important virulence-related factors or endotoxins. However, it is not clear how the presence and status of these epitopes are influenced by environmental stress conditions. In this study, changes of outer membrane epitopes for monoclonal antibodies (mAb) from the Dresden panel and the major outer membrane protein MOMP were analysed for five L. pneumophila strains during short- and long-term starvation in ultrapure water. RESULTS:With ELISA and single cell immuno-fluorescence analysis, we could show that for most of the investigated mAb-strain combinations the total number of mAb-stained Legionella cells stayed constant for up to 400 days. Especially the epitopes of mAb 3/1, 8/5, 26/1 and 20/1, which are specific for L. pneumophila serogroup 1 subtypes, and the mAb 9/1, specific for serogroup 6, showed long-term persistence. For most mAb- stained cells, a high percentage of viable cells was observed at least until 118 days of starvation. At the same time, we observed a reduction of the fluorescence intensity of the stained cells during starvation indicating a loss of epitopes from the cell surface. However, most of the epitopes, including the virulence-associated mAb 3/1 epitope were still present with high fluorescence intensity after 400 days of starvation in up to 50% of the starved L. pneumophila population. CONCLUSIONS:The results demonstrate the continuous presence of outer membrane epitopes of L. pneumophila during short-term and long-term starvation. Thus, culture-independent mAb-based diagnostic and detection tools, such as immuno-magnetic separation and microarray techniques are applicable for both L. pneumophila in the culturable and the VBNC state even after long-term starvation but nevertheless require careful testing before application. However, the mere presence of those epitopes is not necessarily an indication of viability or infectivity.

Dataset Information

Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain.

Publications

Combination of Heat Shock and Enhanced Thermal Regime to Control the Growth of a Persistent Legionella pneumophila Strain.

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