Antibiotics are often categorized based on the type of microorganism they target. Below is an outline of common antibiotic classes grouped by their target organisms: 1. Antibacterial Antibiotics (Target Bacteria) Gram-Positive Bacteria • Penicillins • Mechanism: Inhibit cell wall synthesis by binding to penicillin-binding proteins (PBPs). • Examples: Penicillin G, Amoxicillin, Nafcillin • Cepha..