Antibiotics are used to kill or injure bacteria. They are among the most often prescribed medicines by the modern doctor. Penicillin was the first antibiotic and was discovered by accident on a mold culture. It is still used today. There are over 100 different types of antibiotics available for doctors to use to treat something as simple as a infected cut all the way up to a life threatening disease such as meningitis. Antibiotics are only useful in treating bacterial infections, if you have a viral infection antivirals (a different class of medication) must be used. It also important to see a a doctor so that they can prescribe the proper antibiotic that will be most effective in fighting a particular infection.