Fig. 4. Colonization by an antimicrobial CoNS strain is protective against S.aureus.

(A)Anti–S.aureus activity secreted from a representative antimicrobial S. hominis strain (A9) isolated from a non-AD subject. A live colony of S. hominis A9 (upper), conditioned medium (10 μl) from an S. hominis A9 overnight culture (middle), or unconditioned medium [tryptic soy broth (TSB)] served as a negative control were applied on TSB agar containing S.aureus. The black area represents zone of growth inhibition of S.aureus.(B and C) Effect of S. hominis on the survival of S.aureus on ex situ pigskin (B) or S. hominis applied to live mouse skin (C). S.aureus was first applied to skin as described in Materials and Methods. The action of S. hominis A9 was compared to controls, including UV-killed and washed A9 or live S. hominis strains that do not produce AMP activity in solution assay (C4, C5, and C6). All CoNS bacteria were applied at 1 × 10⁵CFU/cm². Data represent means ± SEM of data from five pigskin sheets (B) or six mice (C). (D) Effect of multiple applications of S. hominis A9 on survival of S.aureus on mouse skin. S. hominis A9 strain or vehicle was applied twice a day to mouse back skin colonized by S.aureus over the indicated periods. Skin swabs were collected to count S.aureus survival. Data represent means ± SEM from 10 (day 3) or 5 (day 7) independent mice. *P < 0.05 by two-tailed independent t test.