Ampicillin is indicated primarily for infections typically caused by susceptible gram-negative bacteria: Urinary tract infections Meningococcal meningitis Biliary sepsis Respiratory infections Listeria meningitis Enterococcal infections Some typhoid fever and typhoid carriers Penicillinase-resistant penicillins These drugs (dicloxacillin, nafcillin, cloxacillin, flucloxacillin, and oxacillin) are used primarily for Penicillinase-producing methicillin-sensitive Staphylococcus aureus These drugs are also used to treat some Streptococcus pneumoniae, group A streptococcal, and methicillin-sensitive coagulase-negative staphylococcal infections.