A very interesting paper recently appeared in the PLOS ONE journal, authored by Flores et al. entitled “Microbial Biogeography of Public Restroom Surfaces”. This study, conducted by the Noah Fierer and Rob Knight labs at University of Colorado – Boulder, addressed the diversity of bacteria found at various places in public restrooms. The novel aspect of this research is the use of culture-independent next-generation sequencing to determine bacterial species found in discriminating locations in public restrooms.
The restroom has been one of the greatest inventions in human history – especially from a public health perspective. Without toilets and sinks – not failing to mention the plumbing infrastructure to get waste away from living spaces – disease causing bacteria (and let’s not forget other infectious organisms of the human gut, such as intestinal worms) associated with human waste easily spread from human to human, especially in close living quarters. A fascinating brief overview of the microbial history of toilets (including some great anecdotes featuring toilet visionary Sir Thomas Crapper) and a commentary of this scientific paper, written by Rob Dunn, can be found on the Scientific American Blogs site.
Using barcoded pyrosequencing of the 16S rRNA gene marker, Flores et al. observed bacterial species on ten different surface types (door handles & stall handles – both in and out, faucet handles, soap dispenser, toilet seat, toilet flush handle, floor around toilet and floor around sink) in twelve different (six male and six female) restrooms on the UC-Boulder campus on a single day.
The researchers identified 19 different bacterial phyla on all of the surfaces sampled. The majority of sequences (approximately 92%) could be placed within four phyla, including the Actinobacteria, Bacteriodetes, Firmicutes, and Proteobacteria. Human-associated bacteria were found strongly associated with restroom surfaces, which is not surprising for indoor environments.
Bacterial communities could be categorized by the surfaces they inhabited. On toilets, gut-associated bacteria were the dominant group. Skin-associated bacteria were – not surprisingly – found on surfaces touched by hands, such as door handles. The restroom floor held the greatest diversity of bacteria – some of which were found in low abundance – as these surfaces contained soil associated, as well as human associated, bacteria. Quite interestingly, the researchers found that some of the toilet flush handles contained soil associated bacteria, implying that some restroom users flush toilets with their feet to avoid directly touching the handles.
There were no statistically significant differences between bacterial communities found in female and male restrooms, although the relative abundances of some bacterial groups were gender associated. The bacterial family, Lactobacillaceae, found associated with vaginas, were – not surprisingly – more abundant in and around female restroom toilets than male counterparts.
The authors used the newly developed software package, Source Tracker, to determine the similarity of bathroom surfaces to communities from expected and previously published sources, such as human skin, the human gut, urine, soil, and faucet water. It was predicted that human skin was the primary source of restroom surface bacteria. Human gut was a source of bacteria found on and around toilets. Despite the presence of many typical soil bacterial groups found on restroom floors, soil was not identified as a statistically significant source, probably because soil typically contains a highly diverse taxonomic array of species, many of which are rare. The authors state that custodial mops and ventilation systems may also have some influence on the floor surfaces but were not directly addressed in this study.
The authors show here that human-associated bacteria are the most common microbes found in public restroom surfaces. Human influenced source patterns can be determined from the bacterial community structure within the biogeography of restrooms. This study underscores the importance of hand washing, particularly when using public restrooms, and the techniques used in this paper could be used to track or determine likely pathogenic bacteria found on surfaces during incidents of infectious outbreaks.