| Summary: | <i>Staphylococcus aureus</i> (<i>S. aureus</i>) is one of the well-known agents causing atopic dermatitis (AD) in susceptible individuals, and <i>Staphylococcus epidermidis</i> (<i>S. epidermidis</i>) produces class I thermostable bacteriocins that can selectively kill <i>S. aureus</i>, suggesting protective roles against AD. There is a large need for developing precise therapies only to target <i>S. aureus</i> and not to harm the beneficial microbiome. On the agar well diffusion assay, live planktonic <i>S. epidermidis</i> showed clear zones of inhibition of <i>S. aureus</i> growth, but heat-killed cells and cell-free supernatants did not show this. These results would lead us to hypothesize that cytoplasmic bacteriocin from <i>S. epidermidis</i> will be a promising agent to inhibit <i>S. aureus</i> growth. Therefore, we have extracted a novel thermolabile cytoplasmic bacteriocin from <i>S. epidermidis</i> using trichloroactic acid (TCA)/acetone precipitation method after cell lysis with a SDS-containing buffer. These bacteriocin selectively exhibited antimicrobial activity against <i>S. aureus</i> and methicillin-resistance <i>Staphylococcus aureus</i> (MRSA), presenting no active actions against <i>S. epidermidis</i>, <i>E. coli</i>, and <i>Salmonella</i> Typhimurium. The extracted cytoplasmic bacteriocin compounds revealed several diffuse bands of approximately 40−70 kDa by SDS-PAGE. These findings suggest that these cytoplasmic bacteriocin compounds would be a great potential means for <i>S. aureus</i> growth inhibition and topical AD treatment.
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