Antagonism within populations of micro-organisms from normal human skin

The skin flora of 20 normal subjects was sampled from 7-cm2 sites on the volar forearm, forehead and ball of the foot. Interactions between all aerobic and anaerobic strains isolated from the same site were examined by a deferred-antagonism technique. Seventeen subjects possessed inhibitory strains on at least one skin site. Of the Micrococcaceae tested, 20.6% were inhibitory. Of the aerobic diphtheroids, more strains were sensitive (19.2%) than inhibitory (5.1%). Inhibitory Micrococcaceae and aerobic diphtheroids revealed intergeneric and intrageneric inhibition. Antagonistic propionibacteria were found (7.4%) but no sensitive strains. Several Micrococcaceae were specifically antagonistic towards only one strain isolated from the same skin site; no sensitive strains from other skin sites or other subjects were found. Quantitative sampling showed that only 17.5% of the inhibitory strains clearly dominated their skin sites numerically.