Unnecessary Prescription of Antibiotics Still Prevalent Due to Difficulties in Identifying Antibiotic-Resistant Staphylococcus aureus Community-acquired Pneumonia. Researchers examined the true prevalence of methicillin (antibiotic)-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in the context of community-acquired pneumonia (CAP) – and how the current guidelines affect clinical and antibiotic-selection decisions.