S. aureus Growth and Antibiotic Susceptibility

Primers, strains, and plasmids used in the current study are listed in Table S1 in the supplemental material. All primers for PCR were purchased from Integrated DNA Technologies, Inc. (Coralville, IA). S. aureus was propagated in Bacto tryptic soy broth (TSB; BD, Sparks, MD) or on Difco tryptic soy agar (TSA; BD). To make TSB-c medium (40 (link)), TSB was stirred in the presence of 1% (wt/vol) Chelex 100 beads (Sigma-Aldrich, St. Louis, MO) for 4 h, a treatment that has been shown to reduce the level of available manganese to the low nanomolar range (40 (link)). The medium was then filter sterilized and supplemented with MgCl₂ and FeSO₄ to final concentrations of 50 µM and 1 µM, respectively. All antibiotics were purchased from Sigma-Aldrich and were used at the following concentrations for S. aureus: 5 µg/ml (gentamicin), 10 µg/ml (erythromycin), and 7 µg/ml (chloramphenicol).