Strep is an abbreviation for a family of bacteria called "streptococci." Strep throat occurs when the throat and surrounding structures become infected with this bacteria.
Strep throat should be treated with an antibiotic for many reasons. It reduces the duration of symptoms, prevents the complications associated with local spread, prevents the rare but serious complications of untreated streptococci infections such as rheumatic fever (immune system triggered damage to heart valves) or glomerulonephritis (damaged kidneys), and reduces the spread to close contacts.
Before your doctor prescribes an antibiotic, he will likely verify the cause of your symptoms by performing a rapid strep test. Occasionally, a rapid strep test will have false negative results. For this reason, the culture is always sent to a laboratory for a few days. If the test becomes positive later on, your doctor will notify you and prescribe an antibiotic to treat your illness. The most common antibiotic prescribed for strep throat remains penicillin, though other effective antibiotics can be prescribed for individuals who have penicillin allergies.
Source: Medline Plus. Strep Throat. Accessed: February 14, 2009 from http://www.nlm.nih.gov/medlineplus/ency/article/000639.htm
Medline Plus. Strep Throat. Accessed: February 14, 2009 from http://www.nlm.nih.gov/medlineplus/ency/article/000639.htm