Used to treat a wide range of bacterial infections, including respiratory tract infections, urinary tract infections, meningitis, and gastrointestinal infections. Effective against both Gram-positive and some Gram-negative bacteria. Commonly administered in hospitals and clinics, especially when penicillin-resistant strains are a concern. Also used in veterinary medicine to treat infections in animals. Frequently included in culture media to select for bacteria that have been genetically modified with ampicillin resistance genes.