Materials.

α-Cyano-4-hydroxycinnamic acid (CHCA), acetonitrile, and formic acid were purchased from Merck (Darmstadt, Germany). Trifluoroacetic acid (TFA) was purchased from Adamas Reagent Co. Ltd. (Shanghai, China). Tris(hydroxymethyl)methyl aminomethane (Tris) was purchased from Beijing HWRK Chem Co., Ltd. (Beijing, China). Tryptic soy agar (TSA) and Luria-Bertani (LB) broth were purchased from Beijing Land Bridge Technology Co., Ltd. (Beijing, China). Sterile water was obtained by sterilization at 120°C. Calcium chloride was obtained from Shanghai Chemical Corp. (Shanghai, China). Vancomycin and erythromycin were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China). Tobramycin was purchased from Aladdin Reagent Co., Ltd. (Shanghai, China). S. epidermidis (ATCC 12228), S. aureus (ATCC 25923), K. pneumonia (CICC 21519), and Escherichia coli (ATCC 8739) were purchased from the China Center of Industrial Culture Collection (CICC; Beijing, China) or the American Type Culture Collection (ATCC; Manassas, VA, USA). The M-Discover 100 Excellence MALDI-TOF MS was obtained from Meihua Medical Technology Limited (Zhuhai, China). The Milli-Q deionized water system was obtained from Jingyuan Science & Technology Co., Ltd. (Hangzhou, China). The spectrophotometer and bacterial incubator were obtained from Thermo Fisher Scientific (USA). The centrifuge was obtained from Eppendorf (Germany).