#FEMSmicroBlog: Finding Legionella in shower hoses


Legionella bacteria (including the pathogen Legionella pneumophila) often reside in biofilms in plumbing systems of buildings. Here, they interact with other microbes, influencing positively or negatively their survival or proliferation. The study “Legionella relative abundance in shower hose biofilms is associated with specific microbiome members” in FEMS Microbes found that Legionella is not the only issue of contaminated shower hoses, as explained by Alessio Cavallaro and Frederik Hammes in this #BehindThePaper interview.


Can you summarise the significance of your paper for microbiologists outside of your field?

Legionella are opportunistic pathogens that naturally inhabit building plumbing systems, where they interact with other microbes. We had previously discussed these interactions. In the present study, we analysed 85 samples from one contaminated residential building with molecular techniques.

We found that the presence of certain genera of bacteria or protists predicted the presence or absence of Legionella. When looking at individual sequences, we found strong but variable associations between Amplicon Sequence Variants (ASVs) from species classified as Legionella and ASVs from other members of the microbiome. These observations suggested that specific interactions may occur at a species level.


What can policymakers learn from your research results?

Controlling Legionella-related problems in buildings is mostly addressed with broad-sword engineering-based approaches, like high temperature, disinfectants, etc. Our study highlights the importance of considering Legionella growth in plumbing biofilms in an ecological context. Hopefully, this can help integrate alternative approaches, such as targeted biological-control strategies.

Legal guidelines only consider sampling water to assess Legionella contamination in buildings. We investigated and sampled shower hoses and highlighted them as relevant niches for Legionella contamination. We believe that only sampling water might lead to underestimated Legionella numbers in plumbing systems. A closer look at the biofilm phase would thus be ideal.


What is a surprising finding you stumbled upon while doing your research?

16S rRNA amplicon data is usually (and sensibly) limited to genus-level interpretations. However, our data revealed many unique Legionella-classified ASVs.

The strong correlation between specific Legionella-classified ASVs and ASVs from other microorganisms also surprised us. These interactions at a species level highlight the importance of biofilms in water pipeline settings.

Overview of the average microbial composition - including Legionella - identified in plumbing systems of buildings.
Overview of the average microbial composition identified in plumbing systems. From Cavallaro et al. (2023).

Digital droplet PCR showed that L. pneumophila only represents a small portion of the Legionella genus present in our samples. We found that a broad Legionella diversity seems to be present in biofilms of shower hose. Hence, one question remains: why do different Legionella species prefer different ecological niches?


What was one of the main hurdles you encountered and how did you solve it?

The primary hurdle in this study was the weak annotation of databases for 18S amplicon sequencing data. We used 18S sequencing to classify protists in the samples, as opposed to 16S amplicon sequencing data for bacteria. With 18S amplicon sequencing, we had low levels of identification, with up to 78% of sequences being unclassified at phylum level.

We used what we currently thought was the best-practice approach. This field needs to generate more protist data to populate databases to reach a comparable level with 16S amplicon sequencing data for bacteria.

In the study, we critically comment on the limitations of taxonomic-based approaches to unravel complex community interactions. The most obvious one is the fact that taxonomy does not necessarily reflect function. After all, different species often have similar metabolic abilities!


You decided to opt for the Transparent Peer Review route offered by FEMS Microbes. What motivated you to do so, and what are the benefits in your opinion?

For us, open and transparent publication and reviewing is the only logical way to go. For a PhD student, this simply makes it easier to understand the process and learn what they are going to experience (especially in the case of the first publication).

Additionally, we strongly believe that a transparent reviewing process would encourage reviewers and authors to be better, fairer, and more respectful at their respective tasks. This behaviour would clearly benefit the entire scientific community.


About the authors of this blog

Frederik Hammes is head of the Department of Environmental Microbiology (Eawag) at the Swiss Federal Institute of Aquatic Science and Technology, where he leads the drinking water microbiology group. His research currently focusses on Legionella control in building plumbing systems, as part of a large Swiss-wide Legionella research effort.

Alessio Cavallaro is a 4th year PhD student in the drinking water microbiology group at Eawag. He is a biotechnologist by training and interested in all aspects of microbial ecology and genomics. His PhD research focuses on how Legionella interacts with other microorganisms. He tries to find anti-Legionella compounds as an alternative strategy to control pathogens in the environment.

About this blog section

#BehindThePaper posts on the #FEMSmicroBlog aim to bring science closer to different audiences and to tell more about the scientific or personal journey to come to the results.

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