(mŭl'tē'drŭg-rē-zis'tănt ōr'găn-izmz) Bacteria and other microorganisms that have developed resistance to many antimicrobial drugs (e.g., methicillin/oxacillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin-resistant Streptococcus pneumoniae).