Tuesday, 29 October 2013

The Microbial Community In The Palm Of Your Hand!

Fierer et al used the bacterial diversity on 51 volunteers’ palms to discover the variability between the hands of an individual and the variability between individuals. There is a huge array of bacteria found upon the surface of the human body, with each area of the body having it’s own unique community of microbes.  The presence of a community is dictated by frequency of skin shedding, UV exposure, host anti-microbial defence, moisture availability and exposure to detergents and soaps. This study was conducted upon the dominant and non-dominant hands of each volunteer (handedness).

The 16S rNA genes were amplified using PCR techniques, before being analysed using a pyro-sequencing run; this was conducted for each palm of each volunteer.  This technique, coupled with various bar-coding techniques, provided the most comprehensive dataset of a human skin bacteria diversity to date. 
The study found that the average human palm contains >150 distinct species-level bacteria.  This is a radical difference to previous studies which are noted by the author to have been largely under-estimated. The bacterial richness found in the swabs from a palm were >3 times higher than previous swabs conducted on elbow and forearm skin.  It was hypothesized that the increased bacterial diversity and richness may be due to inoculation due to contact with the surrounding environment though it was suggested that the depth of the survey, which produced rarer bacteria often un-documented, was the root-cause of the heightened richness and diversity.  The results were compared with a previous study that documented the diversity of the throat, stomach and fecal bacteria, collected using similar pyro-techniques; the palms were found to be higher.
               The most abundant genera were found to be Proprionbacterium, Streptococcus, Staphylococcus, Corynebacterium and Lactobacillus which accounted for 94% of the total population.  These are believed to be the most common skin residents.  The other genera were deemed to be either transient, short-term residents or permanent residents that were simply present in low quantities or were only present due to specific host factors.
               Despite similarities, across the 102 palms swabbed, 4,742 distinct bacterial phylotypes were documented; only 5 of which were shared across all hands, showing a huge range of inter-variability.  There was a significant difference in the communities found on the dominant and non-dominant hands, with the dominant hand having a very different community to the non-dominant hand.
               The sex of the volunteer was also found to significantly affect the diversity and abundance of bacteria, with women harbouring 1573% more abundance of several species.  Women were also found to have a higher diversity of bacteria than men.  There were several hypotheses for why this may be; reduced pH in men, increased skin thickness in men, different hormone secretion and frequency of cosmetics applied. It was also reported that women wash their hands more often than men.

               This study explores the techniques involved with microbial identification whilst helping to express the particularity and definition of identification of the skin’s bacterial community.  The technique detailed in this study could be applied to deeper meta-genomic studies.  This study also could help with understanding the behaviours associated with increased hygiene and health. 

Fierer et al (2008) The influence of sex, handedness and washing the diversity of hand surface bacteria. PNAS. 105:46 pp.17994-17999

1 comment:

  1. In addition to this study's explanations for the higher bacterial diversity on hands compared to skin elsewhere; could it also be that hands, being a more heterogeneous habitat with crevices, folds, nails, calluses, etc, have a wider range of micro-niches in which to harbour higher diversity?