Usa300

The MRSA strains (including ATCC 43,300 and USA300), MSSA strains (including ATCC 25,923 and MW2) and Staphylococcus epidermidis RP62A and ATCC 12,228 were purchased form American Type Culture Collection or BNCC BeNa Culture Collection (Beijing, China). Other type strains of Escherichia coli ATCC 25,923, Enterococcus faecalis ATCC 29,212, Klebsiella pneumoniae ATCC 700,603, Acinetobacter baumannii ATCC 19,606 and Pseudomonas aureginosa PAO1 were provided by Luo Juncai (Tiandiren Biotech, Changsha, China). Clinical strains of MRSA were isolated from the Third Xiangya Hospital of Central South University, and identified by Matrix-Assisted Laser Desorption Ionization (BD, Germany). S. aureus and S. epidermidis were grown in Tryptic Soy Broth (TSB), E. faecalis was grown in Brain Heart Infusion (BHI). Other Gram-negative strains were grown in Luria-Bertani (LB) broth. All the culture mediums were purchased form Solarbio (Beijing, China). Chemicals of AKBA and other antibiotics were purchased from the MedChem Express (New Jersey, USA) and dissolved in dimethyl sulfoxide (DMSO) or deionized water.

The MRSA strain USA 300 was obtained from the American Type Culture Collection (ATCC, Manassas, VA, United States) and grown at 37°C in tryptic soy broth (TSB). USA 300ΔsrtA was cultured in TSB supplemented with spectinomycin. The modified oligopeptide used in this study was synthesized by Scilight Biotechnology (Beijing, China) and was dissolved in phosphate-buffered solution (PBS). To improve its pharmacokinetics and therapeutic efficacy, the oligopeptide was modified by PEG2000 modification and amide modification at the N- and C-termini, respectively.