Ecological Analyses of Mycobacteria in Showerhead Biofilms and Their Relevance to Human Health

Abstract

Bacteria thrive in showerheads and throughout household water distribution systems. While most of these bacteria are innocuous, some are potential pathogens, including members of the genus Mycobacterium that can cause nontuberculous mycobacterial (NTM) lung infection, an increasing threat to public health. We found that showerheads in households across the United States and Europe often harbor abundant mycobacterial communities that vary in composition depending on geographic location, water chemistry, and water source, with households receiving water treated with chlorine disinfectants having particularly high abundances of certain mycobacteria. The regions in the United States where NTM lung infections are most common were the same regions where pathogenic mycobacteria were most prevalent in showerheads, highlighting the important role of showerheads in the transmission of NTM infections.

A global survey of mycobacterial diversity in soil

“…Of the 159 lineages detected in our global survey only 3% of the lineages (5/159) encompassed described isolates. These results contrast to a comparable survey of mycobacteria in household plumbing that used the same hsp65 marker gene sequencing approach, where the majority of the mycobacterial lineages included described taxa (7). The high proportion of undescribed mycobacterial lineages we recovered from soil is slightly higher than that reported previously in soils (20) and lakes (12) via 16S rRNA gene analyses.…”

“…While the exact sources of these human NTM infections often remain unclear, water and soil are widely considered the predominant environmental reservoirs of NTM (1, 4, 6). A growing number of studies have focused on potentially pathogenic NTMs in aquatic systems, including residential plumbing systems (7–11), lakes (12, 13), and other aquatic environments (14–18). Much less is known, however, about the biodiversity and ecological preferences of NTM in soil and the relevance of soil-derived NTM to human health.…”

“…While such approaches are clearly useful for addressing specific research questions, typical cultivation-based approaches are likely to underestimate the mycobacterial diversity found in environmental samples due to well-known culturing limitations (32, 34, 35). As such, it is likely that many environmental mycobacteria have remained uncharacterized (7, 36). Second, although PCR-based methods can be used to more broadly survey soil mycobacterial diversity (20, 27, 37, 38), most of these cultivation-independent studies have relied on the PCR amplification and sequencing of regions of the 16S rRNA gene, which often does not provide sufficient resolution to differentiate between distinct species or strains within the Mycobacterium genus (28, 37, 38).…”

Aggregation of nontuberculous mycobacteria is regulated by carbon:nitrogen balance

“…Understanding the environmental niches in which NTM have evolved can lend context to our finding that C:N balance controls aggregation state. NTM are non-motile saprophytes that are common residents of soil and waterways (22, 28, 44). In soil, carbon is most often the limiting nutrient for bacterial growth (45, 46).…”

“…Nontuberculous mycobacteria (NTM) are emerging pathogens that utilize biofilm formation for survival and persistence both in the host and in the non-host environment (18–22). NTM are adept at surviving standard water decontamination protocols and are commonly found in household water systems, often growing as biofilms (18, 23).…”