Antibiotics can be very helpful when they are used for the right reason. However, they do not treat every infection. Antibiotics work against bacteria, not viruses. This means they do not help with many common illnesses, including colds, most sore throats, flu, and many cases of bronchitis. What antibiotics treat Antibiotics are used to treat certain bacterial infections. Examples may include some cases of: Strep throat Urinary tract infection Pneumonia Skin infection Certain