Microbial Ecology of Human Skin

The microbial ecology of human skin is complex, but little is known about its species composition. We examined the diversity of the skin biota from the volar left and right forearms in six healthy subjects using broad-range 16S rDNA PCR-based sequencing of randomly selected clones.

For the initial 1,221 clones analyzed, 182 SLOTUs (species-level operational taxonomic units) belonging to 8 phyla were identified, estimated as 74.0% (95% CI: 64.8%~77.9%) of the SLOTUs in this ecosystem; 48.0±12.2 SLOTU were found in each subject. Three phyla, Actinobacteria, Firmicutes, and Proteobacteria, accounted for 94.6% of the clones. Most (85.3%) of the bacterial sequences corresponded to known and cultivated species, but 98 (8.0%) clones, comprising 30 phylotypes, had <97% similarity to prior database sequences. Only 6 (6.6%) of the 91 genera and 4 (2.2%) of the 182 SLOTUs, respectively, were found in all six subjects.

Analysis of 817 clones obtained 8 to 10 months later from four subjects, showed new phyla (2), genera (28), and SLOTU (65). Only four (3.4%) of the 119 genera (Propionibacteria, Corynebacteria, Staphylococcus, and Streptococcus) were observed in each subject tested twice, but these represented 54.4% of all clones. These results show that the bacterial biota in normal skin is highly diverse, with few well-conserved and well-represented genera, but otherwise low-level interpersonal consensus.

Zhan Gao, MD

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Table 1. Distribution of 2,038 16S rDNA clones from forearm skin of six healthy subjects:

Subject			Number of clones studied
Subject			First sampling			Second sampling
Designation	Age (years)	Sex	Left forearm	Right forearm	Total		Left forearm	Right forearm	Total	Number of months apart
A	41	F	105	103	208		100	103	203	10
B	21	F	103	101	204		NA*	NA*	NA*	NA*
C	31	F	103	99	202		101	105	206	8
D	53	M	101	103	204		NA*	NA*	NA*	NA*
E	54	M	100	103	203		103	99	202	10
F	29	M	102	98	200		102	104	206	8
Total			614	607	1,221		406	411	817

Table 2. Subject samples with links to 2,038 DNA sequences from human forearm skin:

Sequence Identifier	Subject Time1	Sequence Identifier	Subject Time2
AL1(1—119) AR1(1—119)	A1	AL2(2—106) AR2(1—108)	A2
BL1(2—148) BR1(1—150)	B1
CL1(1—122) CR1(1—108)	C1	CL2(1—106) CR2(1—106)	C2
DL1(1—143) DR1(1—138)	D1
EL1(1—104) ER1(1—104)	E1	EL2(1—104) ER2(1—106)	E2
FL1(1—113) FR1(1—106)	F1	FL2(1—106) FR2(2—106)	F2

The study was funded by the National Institutes of Health (NIH), by a Senior Scholar Award from the Ellison Medical Foundation, and by the Diane Belfer Program in Human Microbial Ecology in Health. The authors of the study are Zhan Gao, M.D., Chi-hong Tseng, Ph.D., Zhiheng Pei, M.D., Ph.D., and Martin J. Blaser, M.D.

Blaser Lab