Quantification of the Bacteria on Human Skin

33 pages. A thesis presented to the Department of Biology and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Arts, Fall 2017The skin is a primary interface for human-microbe interaction. Most studies are concerned with determining what bacterial taxa inhabit the skin, rather than the absolute quantities of bacteria inhabiting environmentally distinct dry, moist, and sebaceous skin habitat types. Additionally, few studies have used culture-independent methods to estimate bacterial abundance, and none yet published have determined what proportions of these communities are viable. Described here is the first study comparing colony counting, qPCR, and fluorescence microscopy for quantifying both viable and non-viable skin-associated bacteria. Data from colony counts and fluorescence microscopy showed that there are significantly more bacterial cells/cm2 of skin sampled from sebaceous sites than from dry or moist sites, whereas qPCR showed no difference in the quantity of 16S amplicons between all three sample types. We found from fluorescence microscopy that the lowest cell viability occurred at sebaceous skin sites (6.78%) and the highest at moist sites (15.0%). Additionally, microscopy provided us with estimates of cell density (~107 cells/cm2) that are similar to what has already been reported by other studies of the skin microbiome. These results provide foundational knowledge about the skin microbiome, with potential implications for the study of ecology and human health