Bacteria are said to be resistant to antibiotics if they have developed ways to fight against the effects of these drugs. This means that the drugs are no longer able to kill the bacteria.
This often happens when a drug doesn't fight off all of the bacteria and completely get rid of an infection. The bacteria that are left are the stronger ones (they fought against the drug and survived). These stronger bacteria start to multiply and your infection comes back. But this time you have an infection caused by the strongest of the bacteria, and this makes it less likely that the same antibiotic will work.
Another way that antibiotic resistance develops is if you don't finish taking all of your antibiotics. The process is similar. The bacteria that weren't killed off when you took the first doses of your drug are more likely to grow in a form that can fight against the antibiotic. This is why it is important that you take all of your antibiotic tablets, even if you feel better.
Several strains of the bacteria that cause the most common form of bacterial pneumonia (called pneumococcal pneumonia) are becoming resistant to some antibiotics. This is especially true of penicillins.  But it is also true of other types of antibiotics, including cephalosporins, macrolides, fluoroquinolones, and doxycycline. 
Strains of the pneumococcus bacteria that are resistant to penicillin are often also resistant to other frequently used antibiotics, such as erythromycin and tetracycline.
When your doctor decides which antibiotic to use to treat your pneumonia, he or she will take into account whether there is antibiotic resistance in the area where you live.
These medicines are used to help your immune system fight infection. There are a number of different types of antibiotics that work in different ways to get rid of bacteria, parasites, and other infectious agents. Antibiotics do not work against viruses.
Bacteria are tiny organisms. There are lots of different types. Some are harmful and can cause disease. But some bacteria live in your body without causing any harm.
You get an infection when bacteria, a fungus, or a virus get into a part of your body where it shouldn't be. For example, an infection in your nose and airways causes the common cold. An infection in your skin can cause rashes such as athlete's foot. The organisms that cause infections are so tiny that you can't see them without a microscope.
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