Antibiotic Susceptibility Testing

A 52-year-old man from Mumbai with a 10-day history of fever and productive cough is admitted with community-acquired pneumonia. Sputum culture yields Staphylococcus aureus. The isolate is tested by the broth microdilution method, and the minimum inhibitory concentration (MIC) for oxacillin is 0.5 µg/mL. The CLSI breakpoint for oxacillin against S. aureus is: susceptible ≤2 µg/mL, resistant ≥4 µg/mL. What is the most appropriate interpretation and clinical action?

In the E-test (Etest) method for antibiotic susceptibility testing, the minimum inhibitory concentration (MIC) is determined by which of the following?

A 38-year-old woman from Delhi presents with a 5-day history of dysuria, urinary frequency, and suprapubic tenderness. Urine culture grows a gram-negative rod. The isolate is tested on Mueller-Hinton agar using the Kirby-Bauer disk diffusion method. A ceftriaxone disk (30 µg) is placed on the plate, and after 18 hours of incubation at 35°C, the zone of inhibition measures 22 mm. According to CLSI standards for Enterobacteriaceae, what is the susceptibility interpretation of this isolate?