Thursday, 26 July 2012

Unseen coworkers: office space bacteria

If you're a germophobe, you won't want to read a recent PLoS ONE report detailing the abundance and diversity of bacteria inhabiting urban office spaces. That's because researchers from San Diego State University and the University of Tucson found almost 4,000 "operational taxonomic units" (or, for lack of a better word, species) belonging to >500 genera across 20 bacterial divisions--all in just 54 offices distributed across 3 cities. Groups most commonly represented include Proteobacteria, Firmicutes, and Actinobacteria--all of which include pathogenic members that can cause serious infections in humans. San Francisco workers can congratulate themselves on having the lowest bacterial abundances measured in the study; likewise, female readers can feel smug about the fact that office spaces belonging to women had significantly fewer bacteria than those utilized by men. Those looking to minimize contact with microbes should take particular care near phones and chairs; researchers found that these harbored much higher bacterial abundances than the other office surfaces they sampled.

(This study highlights a whole new reason why hand-washing is important at work. Image courtesy of Gary Fage.)

Contrary to what you might think, the study wasn't designed to make your skin crawl, but instead to improve our understanding of the "dynamic microbial environments" found in anthropogenic areas. Although previous studies have examined bacterial diversity in popular human hangouts like schools, houses, and airplanes, very little work has focused on offices--where millions of people worldwide spend the bulk of their time each day. Developing a "baseline" of bacterial diversity in offices may be useful for understanding the dynamics behind infectious outbreaks, as well as for determining which features of office buildings--including microclimate and space usage patterns--contribute to the spread of pathogens.

To collect their samples, the researchers visited 30 offices (15 belonging to men, 15 belonging to women) in each of 3 cities (San Francisco, New York, and Tucson). In each office, they swabbed similar-sized patches of the same 5 surfaces: chairs, phones, computer mice, computer keyboards, and desktops. A cell-counting assay revealed that chair and phone surfaces contained the highest levels of bacterial DNA, and so samples from these locations (n = 54 offices) were subjected to "deep-sequencing" analyses that allowed the researchers to identify bacteria down to the genus level. The resulting genera abundance patterns were then correlated with city, surface type, and sex of (human) office inhabitant.

(E. coli, one of many types of Proteobacteria. Image courtesy of the Encyclopedia of Life.)

According to the researchers, sex-related variations in bacterial abundances likely stem from the fact that men are known to wash their hands and brush their teeth less frequently than women (a claim supported by actual scientific research). Additionally, men are generally larger than women, and therefore possess a greater surface area that can transport and shed hitchhiking bacteria.

Indeed, humans were "clearly the primary source of office bacterial contamination," as shown by the fact that the most common genera are known to inhabit human skin or cavities. However, the study also revealed a surprising prevalence of bacteria associated with the human digestive tract--potentially suggesting that post-bathroom-visit hand-washing behaviors could be improved among office workers. Environmental microbes were also common, though researchers were surprised that this category included thermophilic bacteria that are normally associated with hot springs. This result indicates that this hardy group of species is capable of dispersing--and surviving--over quite an impressive range. In fact, the researchers suggest that sampling techniques such as the ones used in this study might be helpful for performing future in-depth investigations of microbe dispersal in general.

 (Image courtesy of XMDR.)

One other useful follow-up study will be an examination of diversity at the level of species and strains. However, this will require the development of "easier and less expensive" techniques. Such studies may be useful not only for illuminating the spread of disease--as mentioned above--but also the spread of genes: Bacteria often share genetic material with their neighbors through the process of horizontal, or lateral, gene transfer. Thus, data on which species intermingle in modern human environments may allow scientists to better understand and predict the evolution of microbes in anthropogenic areas.

Hewitt, K.M., Gerba, C.P., Maxwell, S.L., and Kelley, S.T. 2012. Office space bacterial abundance and diversity in three metropolitan areas. PLoS ONE 7(5):e37849.

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