OD measurements and calculated growth rates

Standard bacteriological media MHB (Sigma-Aldrich) was supplemented with 25 mg/L Ca2+ and 12.5 mg/L Mg2+ (CA-MHB). Eukaryotic cell culture media Roswell Park Memorial Institute 1640 (RPMI) (Thermo Fisher Scientific) was supplemented with 10% LB (R10LB). Broth microdilution was performed to determine the nafcillin MIC in each media condition. On the day of the experiment, overnight cultures of HA-MRSA D592 were diluted to a starting OD600 of 0.01 into fresh media and grown at 37°C with stirring to OD600 0.4. This preculture was then diluted back to OD600 0.01 into fresh media containing no drug or sub-inhibitory concentrations of nafcillin relative for each media type. Growth was monitored by obtaining OD600 readings every 45 min for 6 hr. Three biological replicates were collected for the study, each derived from different colony and overnight culture.本研究使用的标准细菌学培养基为穆勒-欣顿肉汤（MHB，Sigma-Aldrich），向其中添加25 mg/L钙离子与12.5 mg/L镁离子后，得到CA-MHB培养基。真核细胞培养基采用罗斯威尔帕克纪念研究所1640培养基（RPMI，赛默飞世尔科技），向其中添加10% LB培养基后，得到R10LB培养基。采用肉汤微量稀释法测定各培养基条件下萘夫西林的最低抑菌浓度（MIC，Minimum Inhibitory Concentration）。实验当日，将医院获得性耐甲氧西林金黄色葡萄球菌（HA-MRSA）D592的过夜培养物稀释至初始OD₆₀₀为0.01，接种至新鲜培养基中，于37℃搅拌培养至OD₆₀₀达到0.4。随后将该预培养物再次稀释至OD₆₀₀为0.01，接入不含药物或针对各培养基的萘夫西林亚抑菌浓度的新鲜培养基中。每45分钟测定一次OD₆₀₀值，持续6小时以监测菌体生长情况。本研究共设置3次生物学重复，每一次重复均来自独立的单菌落过夜培养物。