Fig. 1

QTOF MS spectrum and ion chromatograms of PSMs. a QTOF MS spectrum of PSMs in the mixed standard solution. b Extracted ion chromatograms of PSMs in USA 300 culture supernatant: 1, PSMβ2 (m/z 1495.4609); 2, PSMα3 (m/z 879.1432); 3, PSMα2 (m/z 769.4640); 4, PSMα1 (m/z 1144.6796); 5, δ-toxin (m/z 1503.8245); 6, PSMβ1 (m/z 1508.8015); 7, PSMα4 (m/z 734.1283)