The antibiotic with the largest diffusion ring into the staphylococcus aureus was the penicillin, it acted on the bacteria effectively, then it mutated, became resistant in some cases and had to be treated with ampicillin as well, along with other antibiotics such as oxacillin, vancomycin, nafcillin, among others. Less than 5% of the s. aureus is resistant to penicillin, making it the best option for treatment today