<p>(A) Representative images of the colony-spreading activity of MRSA NI strains stimulated by calf serum. Overnight cultures of MRSA NI strains were spotted onto soft agar plates supplemented with or without calf serum (250 µl/plate) and incubated for 8 h. (B) Colony-spreading response of CA-MRSA strains to calf serum. Overnight cultures of MW2 (USA400, open circles) or FRP3757 (USA300, filled circles) were spotted onto soft agar plates supplemented with 2-fold serially diluted calf serum and incubated for 8 h. The halo diameter was measured. (C) Amount of PSMα3 in MRSA strains cultured in the presence or absence of calf serum. MRSA strains with high colony-spreading response against calf serum (NI-15, MW2, FRP3757, NI-5, NI-7, NI-27, NI-29, NI-36, and NI-38) were cultured in the presence or absence of 1.25% (v/v) calf serum and the culture supernatants were analyzed by HPLC as described previously <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097670#pone.0097670-Kaito4" target="_blank">[6]</a>. Asterisks means not detected.</p
