Background Legionnaires' disease (LD) is a severe form of pneumonia caused by inhalation of aerosols containing Legionella spp., most commonly L. pneumophila, which proliferates within protozoa embedded in established biofilms of engineered water systems, such as shower systems. Despite water management plans, durable control of L. pneumophila at terminal outlets remains challenging, partly because the effects of disinfection treatments on microbial community assembly, ecological interactions, and functional organization within biofilms are poorly understood. This study aimed to investigate how an emerging water/vapor disinfection treatment reshapes shower biofilm microbiomes at critical developmental stages — from early adhesion and biomass peak when L. pneumophila first appears, to mature biofilms associated with pathogen persistence — relative to conventional hot water disinfection, and to identify microbial taxa and functions selectively affected by these interventions. Results We applied a sequential water flushing followed by high-pressure vapor (120℃) protocol either during early biofilm formation or on mature biofilms, all grown on standardized shower systems installed in healthcare, nursing home, and residential buildings subject to L. pneumophila routine control. Compared with conventional thermal disinfection of shower systems (65 °C, 10 min), water–vapor treatment more effectively removed established biofilm communities as supported by scanning electron microscopy, flow cytometry of residual cells, and culture. Amplicon sequencing of the V3-V4 region of 16S rRNA genes revealed treatment-specific shifts in microbial community composition and predicted functional profiles (R2 = 0.285, p = 0.001). Beyond Legionella removal, water–vapor treatment disrupted 70 metabolic pathways (FDR < 0.05), including pathways related to lipopolysaccharide synthesis, central metabolism, and the Legionella-specific CMP-legionaminate pathway, indicating selective impacts on biofilm integrity and pathogen-supportive functions. Conclusion Water–vapor treatment induces substantial ecological restructuring of shower biofilm microbiomes, affecting both taxonomic composition and functional capacity associated with biofilm resilience and pathogen persistence. These findings support that perturbation of key ecological functions within built-environment microbiomes can influence opportunistic pathogen dynamics and encourage the development of microbiome-informed strategies to complement conventional water safety management, particularly in healthcare settings. <MediaObject ID="MOESM3"> <VideoObject FileRef="MediaObjects/40168_2026_2355_MOESM3_ESM.mp4" VideoID="2VEwLoZoQwtE1k4FNMGmdB"> <Caption Language="En" xml:lang="en"> <CaptionContent> Video Abstract </CaptionContent> </Caption> </VideoObject> </MediaObject>

Water–vapor treatment of shower systems in healthcare facilities: reshaping built-environment microbiomes to improve Legionella control and protect at-risk patients

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2026年3月16日

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Tian You,
Pryanka Parmar,
Guillaume Decke,
Kyle Baikie,
Lilian Ryckewaert,
Alexis Marette,
Hélène Niculita-Hirzel

摘要

Background

Legionnaires' disease (LD) is a severe form of pneumonia caused by inhalation of aerosols containing Legionella spp., most commonly L. pneumophila, which proliferates within protozoa embedded in established biofilms of engineered water systems, such as shower systems. Despite water management plans, durable control of L. pneumophila at terminal outlets remains challenging, partly because the effects of disinfection treatments on microbial community assembly, ecological interactions, and functional organization within biofilms are poorly understood. This study aimed to investigate how an emerging water/vapor disinfection treatment reshapes shower biofilm microbiomes at critical developmental stages — from early adhesion and biomass peak when L. pneumophila first appears, to mature biofilms associated with pathogen persistence — relative to conventional hot water disinfection, and to identify microbial taxa and functions selectively affected by these interventions.

Results

We applied a sequential water flushing followed by high-pressure vapor (120℃) protocol either during early biofilm formation or on mature biofilms, all grown on standardized shower systems installed in healthcare, nursing home, and residential buildings subject to L. pneumophila routine control. Compared with conventional thermal disinfection of shower systems (65 °C, 10 min), water–vapor treatment more effectively removed established biofilm communities as supported by scanning electron microscopy, flow cytometry of residual cells, and culture. Amplicon sequencing of the V3-V4 region of 16S rRNA genes revealed treatment-specific shifts in microbial community composition and predicted functional profiles (R² = 0.285, p = 0.001). Beyond Legionella removal, water–vapor treatment disrupted 70 metabolic pathways (FDR < 0.05), including pathways related to lipopolysaccharide synthesis, central metabolism, and the Legionella-specific CMP-legionaminate pathway, indicating selective impacts on biofilm integrity and pathogen-supportive functions.

Conclusion

Water–vapor treatment induces substantial ecological restructuring of shower biofilm microbiomes, affecting both taxonomic composition and functional capacity associated with biofilm resilience and pathogen persistence. These findings support that perturbation of key ecological functions within built-environment microbiomes can influence opportunistic pathogen dynamics and encourage the development of microbiome-informed strategies to complement conventional water safety management, particularly in healthcare settings.

Video Abstract