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How Do Antibiotics Work?

By HERWriter
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How Do Antibiotics Eliminate Bacterial Infection? Lev Dolgachov/PhotoSpin

Have you ever wondered how antibiotics actually make a urinary tract or strep throat infection go away?

Antibiotics were first developed in 1928 when a researcher named Alexander Fleming noticed that the mold Penicillium notatum had stopped the growth of Staphylococcus in a petri dish. Staphylococcus is a type of bacteria that can cause skin infections.

He found that penicillin could also stop the growth of other bacteria such as streptococcus, meningococcus and diphtheria bacillus.

Antibiotics only work against bacteria. They cannot treat a viral infection, so taking them to fight a cold or the flu will not work. It will only make it harder to treat future bacterial infections, due to antibiotic resistance from their overuse.

There are good bacteria that are important for the balance inside your body, and bad bacteria that grow on contaminated surfaces. There are also times when good bacteria that belongs in one place of your body gets a foothold and can grow where it doesn’t belong.

For example, E. coli is supposed to live in your colon. When it finds its way up the urethra to your bladder, then you can develop a urinary tract infection.

Bacteria are classified into two groups: Gram-positive or Gram-negative. This differentiation helps define the type of cell wall the bacteria have. In the lab they can test for which type of bacteria it is by using stain and viewing the bacteria under a microscope.

After they have identified the bacteria, then they can test to see which antibiotic can best fight the bacteria. This is called testing for the bacteria’s sensitivity.

All antibiotics work by one of two methods:

1) Bactericidal antibiotics interfere with the building of the bacteria’s cell wall so they directly kill the bacteria. Penicillin works this way.

2) Bacteriostatic antibiotics interfere in the bacteria’s ability to multiply. Tetracycline is this type of antibiotic as it blocks the bacteria’s ability to make a certain type of protein it needs. Sulfa drugs are bacteriostatic, as they interfere with the bacteria’s DNA and RNA so it cannot duplicate.

The ability for an antibiotic to fight against a particular infection gets back to the type of cell wall the bacteria have.

Gram-positive bacteria have a thin single cell wall surrounding the bacterial cell that is easily permeated. Streptococcus and Staphylococcus are examples of this type of bacteria.

Gram-negative bacteria, like E. coli, have a thicker two-celled wall surrounding it.

The final piece of information about how antibiotics work is that some are narrow spectrum, which can only fight against a specific type of bacteria and others are broad spectrum and can fight against a wider range of bacteria.

The doctor decides which antibiotic is best, based upon several factors. These factors are knowledge of the type of bacteria that typically causes a particular infection such as a skin infection and/or whether or not a lab culture was sent and the specific bacteria was identified.

Here are some guidelines for taking antibiotics.

1) Take the antibiotic prescribed by your doctor for the entire time you are supposed to, even if you are feeling better after only taking it for a few days. The reason is that stopping early can contribute to your body developing bacteria that are resistant to that antibiotic.

2) Check to see if you are to take the antibiotic with or without food or milk, and any interactions they may have to other drugs or antacids. This way you get the most benefit from its action.

3) Consider taking a probiotic with the antibiotic to help maintain the “good” bacteria in your body.

The antibiotic does not know which bacteria are the “good” guys which should be left alone. Taking a probiotic may help reduce your incidence of GI issues or yeast infections if you are a woman.

4) Call your doctor if, after a few days, it seems like the antibiotic is not helping. It is possible that a different bacterium is the one causing your problem, and he may want to switch you to another.


How do antibiotics work? How Stuff Works. Retrieved June 7, 2015.

Types of Antibiotics: Bactericidal vs. Bacteriostatic & Narrow Spectrum vs. Broad Spectrum. Chapter 18 / Lesson 1. Retrieved June 7, 2015.

Antibiotics: How Do Antibiotics Work? MediLexicon International Ltd, Retrieved June 7, 2015.

Using Antibiotics Wisely. WebMD. Retrieved June 7, 2015.

Do Antibiotics Cause Yeast Infections? Everyday Health.com. Retrieved June 7, 2015.

Michele is an R.N. freelance writer with a special interest in woman’s healthcare and quality of care issues.

Edited by Jody Smith

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.

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