Your body has millions of bacteria, inside and out. Bacteria cover your skin, live in your intestines and inhabit your private parts. Typically bacteria live in balance. Some help bodily processes along, while others keep potentially harmful bacteria in check. A bacterial infection can occur though when harmful bacteria enter your body or existing bacteria get out of balance. While there are thousands of kinds of bacteria, only a few kinds actually cause disease in humans.

The usual suspects

Here are some of the most common causes of bacterial infections:.

• Staph or staphylococci. These often harmless bacteria commonly live in and on the body. Some varieties, though, can cause disease or infections.
• • MRSA, or methicillin-resistant Staphylococcus aureus,is a type of staph. It gets its name because it has mutated over time to develop a resistance to most antibiotics used to treat it. It can cause a skin infection that can become very serious and difficult to treat.
• Strep or streptococci. Strep are common bacteria. Some types can cause infections such as strep throat or other respiratory infections, including pneumonia.
• Haemophilus influenzae. These are another common type of bacteria that can sometimes cause infections. Harmful types can cause diseases that include respiratory infections, ear infections or a type of meningitis. Children are now immunized against one disease-causing type called haemophilus influenzae type b (Hib).
• E Coli. These bacteria commonly live in the GI tract of animals and humans. There are some kinds, though, that cause severe diarrhea. They can cause food poisoning if transmitted through improperly cooked hamburger, or other food products that have been contaminated.
• H. Pylori. These bacteria are a common cause of stomach ulcers.
• Salmonella. This is another foodborne pathogen that causes diarrhea or other symptoms of food poisoning. Raw or undercooked eggs or poultry are often the cause of salmonella infection.

How do I know I have a bacterial infection?
A bacterial infection usually makes you noticeably sick. The immune system revs up to fight offending bacteria. This often causes fever, as well as swelling, discharge and pain in the affected area. Sometimes the body will try to get rid of the bacteria through diarrhea or vomiting. But these symptoms can be due to non-bacterial illnesses too. So, it's best to check with your doctor if you have any symptoms of infection. Through examination and sometimes tests, your doctor can determine whether an illness is bacterial and treat it properly.

How are bacterial infections treated?
Mild infections sometimes go away on their own, but see your doctor if you think you may have an infection. Often, you need an antibiotic. Antibiotics kill bacteria, or at least interrupt their ability to multiply. This lets your body's defenses catch up and overtake the offender.

Antibiotics only work against bacteria. They do not work against viruses. So, if you're sick and your doctor says an antibiotic won't help you, you probably have a virus instead of a bacterial illness.

Why do I get different antibiotics for different types of infection?
Some antibiotics can kill bacteria by interrupting part of their reproductive process. Some slow their growth or stop them from multiplying until your body's immune system can kill them. Each class of antibiotics targets a specific bacterial process. The classes are:

• Penicillins
• Cephalosporins
• Tetracyclines
• Aminoglycosides
• Quinolones
• Macrolides

Some are called "broad spectrum" antibiotics. They are effective against a wide variety of bacteria. Other types of antibiotics are targeted to a specific type of bacteria.