Transmission Electron Microscopy of MRSA

MRSA exponential-phase cultures were obtained by diluting overnight cultures with MH broth to the 0.5 McFarland standard (approximately 1.5 × 10⁸ colony-forming units [CFU]/mL) in MH broth. The inoculum was then diluted tenfold (v/v) in MH broth. When MRSA cultures reached the midlogarithmic phase (approximately 1.5 × 10⁶ colony-forming units [CFU]/mL), they were treated with 7.8 μg/mL and 15.6 μg/mL of SKN for 10 h. Then, 2 mL of the cultures was centrifuged at 10,000 ×g for 10 min, and the pellets were treated with Karnovsky's fixative and examined under an energy-filtering transmission electron microscope (LIBRA 120; Carl Zeiss, Oberkochen, Germany) at an accelerating voltage of 100 kV. Images were obtained using a 4 k × 4 k slow-scan charge-coupled device camera (Ultrascan 4000 SP; Gatan, Pleasanton, CA, USA) attached to the microscope [23 (link), 24 (link)].