Continuous-culture studies of interactions among human skin-commensal bacteria

Chemostat studies were made of an antibiotic-producing Staphylococcus epidermidis strain (S6+), a similar, but antibiotic non-producing S. epidermidis strain (S6-), and a sensitive indicator strain of Micrococcus sp. (M7). Pure and mixed continous cultures were investigated at low population levels (in 0-1% peptone water) and at higher levels (in 0-5% peptone water). Strain S6+ antagonised the growth of strain M7 when its colony count was maintained above 10(7-0) per ml, while strain S6- remained unaffected.