What is the primary function of an antibiotic?

The primary function of an antibiotic is to treat an illness, specifically bacterial infections. Antibiotics work by targeting and killing bacteria or inhibiting their growth, which helps the body to recover from infections that may arise. They are crucial in the management of various infectious diseases that can affect humans, animals, and plants.

When an individual or animal is suffering from a bacterial infection, antibiotics are administered to combat the pathogens causing the illness, allowing the immune system to more effectively clear the infection. This use is essential in both human medicine and veterinary practices.

The other options relate to different aspects of health care and wellness. Preventing illness involves vaccinations or certain health behaviors rather than treating existing conditions. Providing nutrition focuses on the dietary intake of nutrients necessary for maintaining health. Supporting immune function encompasses a broad range of practices, including a balanced diet, regular exercise, and good hygiene, rather than specifically involving the action of antibiotics. Thus, the direct and focused role of antibiotics is unequivocally to treat illnesses caused by bacterial infections.