FIG 3.

Ten different strains of D. pigrum inhibit methicillin-resistant S. aureus USA300 strain JE2 whereas S. aureus does not inhibit D. pigrum. (A) Ten pregrown D. pigrum isolates produced a diffusible activity that inhibited the growth of S. aureus strain JE2. (B) When S. aureus was pregrown in this assay, there was no visible inhibition of subsequently inoculated D. pigrum. (C) Similarly, we did not observe any inhibition in a pairwise comparison of three representative strains of D. pigrum in this assay. All growth was on BHI agar in the independent experiments (n ≥ 3) represented in panels A, B, and C. Representative images are shown for each strain. The respective pregrown strain (D. pigrum or S. aureus) was resuspended in PBS, and then a 5-μl drop was placed on BHI agar and pregrown for 48 h (D. pigrum) or 24 h (S. aureus). After that, the indicator strain was inoculated at a location adjacent to the pregrown strain. Inhibition was assessed after 24 and 48 h (48-h results are shown here). For panels A and B, similar results were observed using S. aureus Newman.