Antibiotic usually kill bacteria or stop them from multiplying,but certain bacteria are naturally resistant to a specific antibiotic, which means that antibiotic don't work against them. When antibiotics are used frequently or not used correctly, new problem emerged. Specific bacteria previously considered sensitive to a drug had become resistant and were responsible for treatment failures; this is referred to as acquired resistance. Example is Staphylococcus aureus, which was originally sensitive to penicillin G; most strains are now resistant. The reason for the resistance in this case was due to the production of an enzyme by the bacteria, called a penicillinase that was able to destroy the antibiotic. Studies has shown that bacteria are very good in finding ways of becoming resistant, that is why there is a continuing need for new and improved drug.

Fortunately, new antibiotics have been found that are active against these resistant bacteria. Modification of penicillin and cephalosporin has produced new antibiotics that are resistant to degradative enzymes. For instance, penicillin G was chemically modified to yield the related antibiotic methicillin. In this case methicillin was no longer destroyed by a Staphylococcus aureus enzyme (penicillinase) that inactivated penicillin G.

How to minimize the risk of bacterial resistance:

• Use antibiotic as prescribed by your doctor. It is only effective if taken for the full amount of time prescribed. Never take it longer than prescribed.
• Never take the antibiotic that is prescribed to another family member, because different bacteria may be causing your illness.
• Treat only bacterial infection. Don't take antibiotics for viral illnesses like colds or flu.

How to choose the right antibiotic? A wide array of antibiotics is now available to the physician who has to treat an infection. First, the doctor needs to know what microbe is responsible for the illness and to which antibiotics it is sensitive. For this reason an attempt will frequently be made to isolate the microbe from the patient and test its sensitivity to commonly used antibiotics. With this knowledge in hand the doctor is able to make a rational choice of drug. But if the patient needs an immediate treatment and there is not enough time for doctors to identify the offending microbe, the doctor often just prescribes an antibiotic based on an educated guess.

Ways of Administering Antibiotics: Orally, Topically, Intramuscular injection, Intravenous injection (used in a hospital setting where patients is usually seriously ill), Prophylactically