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.