Extended water stagnation in buildings during the COVID-19 pandemic increases the risks posed by opportunistic pathogens.

The regrowth and subsequent exposure of opportunistic pathogens (OPs) whilst reopening buildings that have been locked down due to the stay-at-home restrictions to limit the spread of COVID-19, is a public health concern. To better understand such microbiological risks due to lowered occupancy and water demand in buildings, first and post-flush water samples (n = 48) were sampled from 24 drinking water outlets from eight university buildings in two campuses (urban and rural), with various end-user occupancies. Both campuses were served with chlorinated water originating from a single drinking water distribution system in South-East Queensland, situated 14 km apart, where the rural campus had lower chlorine residuals. Culture-dependent and culture-independent methods (such as flow cytometry, qPCR and 16S rRNA gene amplicon sequencing) were used concurrently to comprehensively characterise the OPs of interest (Legionella spp., Pseudomonas aeruginosa, and nontuberculous mycobacteria (NTM)) and the premise plumbing microbiome. Results showed that buildings with extended levels of stagnation had higher and diverse levels of microbial growth, as observed in taxonomic structure and composition of the microbial communities. NTM were ubiquitous in all the outlets sampled, regardless of campus or end-user occupancy of the buildings. qPCR and culture demonstrated prevalent and higher concentrations of NTM in buildings (averaging 3.25 log10[estimated genomic copies/mL]) with extended stagnation in the urban campus. Furthermore, flushing the outlets for 30 minutes restored residual and total chlorine, and subsequently decreased the levels of Legionella by a reduction of 1 log. However, this approach was insufficient to restore total and residual chlorine levels for the outlets in the rural campus, where both Legionella and NTM levels detected by qPCR remained unchanged, regardless of building occupancy. Our findings highlight that regular monitoring of operational parameters such as residual chlorine levels, and the implementation of water risk management plans are important for non-healthcare public buildings, as the levels of OPs in these environments are typically not assessed.

Characterizing the premise plumbing microbiome in both water and biofilms of a 50-year-old building.

The premise plumbing portion of drinking water distribution systems (DWDS) has several characteristics that may favor microbial growth in the form of biofilms. These microbial communities are implicated as infectious sources for the spread of opportunistic waterborne pathogens by supporting their complex ecology and transmission through DWDS outlets to susceptible individuals. However, there is limited understanding of the drinking water biofilms in real premise plumbing networks due to challenges with accessibility. Using a combination of culture-dependent and culture-independent approaches, this study comprehensively characterized the premise plumbing microbiome of a 50-year-old university building, inclusive of water and biofilm samples. Microbial diversity in the water samples were more taxonomically diverse in comparison to the mature drinking water biofilms, which were dominated with biofilm-formers and opportunistic pathogens, such as Mycobacterium spp. A model opportunistic pathogen, Legionella spp., was only detectable in water samples using quantitative PCR but could not be detected in any of the drinking water biofilms using either qPCR or culture-dependent approaches, highlighting the limitations of detection methods in these environments. This study presents preliminary findings on the microbial dynamics and complexity in premise plumbing networks, which may support public health management and the development of strategies to eliminate microbial risks to human health.

Microbial phylogenetic and functional responses within acidified wastewater communities exhibiting enhanced phosphate uptake.

Acid stimulated accumulation of insoluble phosphorus within microbial cells is highly beneficial to wastewater treatment but remains largely unexplored. Using single cell analyses and next generation sequencing, the response of active polyphosphate accumulating microbial communities under conditions of enhanced phosphorus uptake under both acidic and aerobic conditions was characterised. Phosphorus accumulation activities were highest under acidic conditions (pH 5.5>8.5), where a significant positive effect on bioaccumulation was observed at pH 5.5 when compared to pH 8.5. In contrast to the Betaproteobacteria and Actinobacteria dominated enhanced biological phosphorus removal process, the functionally active polyP accumulators at pH 5.5 belonged to the Gammaproteobacteria, with key accumulators identified as members of the families Aeromonadaceae and Enterobacteriaceae. This study demonstrated a significant enrichment of key polyphosphate kinase and exopolyphosphatase genes within the community metagenome after acidification, concomitant with an increase in P accumulation kinetics.