Molecular analysis of shower curtain biofilm microbes

Abstract

Households provide environments that encourage the formation of microbial communities, often as biofilms. Such biofilms constitute potential reservoirs for pathogens, particularly for immune-compromised individuals. One household environment that potentially accumulates microbial biofilms is that provided by vinyl shower curtains. Over time, vinyl shower curtains accumulate films, commonly referred to as "soap scum," which microscopy reveals are constituted of lush microbial biofilms. To determine the kinds of microbes that constitute shower curtain biofilms and thereby to identify potential opportunistic pathogens, we conducted an analysis of rRNA genes obtained by PCR from four vinyl shower curtains from different households. Each of the shower curtain communities was highly complex. No sequence was identical to one in the databases, and no identical sequences were encountered in the different communities. However, the sequences generally represented similar phylogenetic kinds of organisms. Particularly abundant sequences represented members of the alpha-group of proteobacteria, mainly Sphingomonas spp. and Methylobacterium spp. Both of these genera are known to include opportunistic pathogens, and several of the sequences obtained from the environmental DNA samples were closely related to known pathogens. Such organisms have also been linked to biofilm formation associated with water reservoirs and conduits. In addition, the study detected many other kinds of organisms at lower abundances. These results show that shower curtains are a potential source of opportunistic pathogens associated with biofilms. Frequent cleaning or disposal of shower curtains is indicated, particularly in households with immune-compromised individuals.

FIG. 1.

Epifluoresence microscopy of biofilm samples SC4 (A and B) and SC2 (C) stained with DAPI (Materials and Methods).

FIG. 2.

Results of phylogenetic analyses with Sphingomonas spp.-related (A) and Methylobacterium spp.-related (B) 16S rRNA sequences obtained in this study. The analyses performed were based on alignments of approximately 670 nucleotide positions. The alignments included cultured Sphingomonas and Methylobacterium spp. and outgroup γ-proteobacteria (Escherichia coli L10328), β-proteobacteria (Nitrosospira mutiformis L35509), and α-proteobacteria (Roseobacter denitrificans M59063). The phylogenetic trees shown were estimated by using ML. MP and NJ analyses converged on very similar tree topologies. Filled circles indicate both MP and NJ bootstrap support exceeding 70%, and open circles indicate bootstrap support exceeding 50%. (See Materials and Methods for details on the phylogenetic and bootstrap analyses.).

FIG. 3.

Compositions of rRNA gene libraries obtained from shower curtain samples. Numbers of clones of each rRNA gene sequence from libraries are grouped as identified on the pie charts as follows: Methylobact, Methylobacterium spp.; Sphingom, Sphingomonas spp.; α-Protbact, α-proteobacteria; δ-Protbact, δ-proteobacteria; γ-Protbact, γ-proteobacteria; Actinomy, Actinomycetales; hGCgpbact, high-G+C gram-positive bacteria; CFBgroup, Cytophaga-Flavobacteria-Bacteroides group; Sphingobac, sphingobacteria.