How Antibiotics Work

Prior to the discovery of antibiotics, there were inevitably only two options to treat an infection: remove the infected tissue, or hope the body recovered on its own. Many infections could not be removed due to location or severity and would eventually kill the host.

The Discovery of Antibiotics

Antibiotics were first discovered in 1928, by accident. Alexander Fleming, a Scottish biologist, returned to his lab after a weekend off to find that a strange mold had grown unattended in one of his Petri dishes. The mold, Penicillium notatum, had actually stopped the growth of the Staphylococcus bacteria. Staph was a well-known bacteria for causing skin infections, pneumonia, foodborne illnesses, and other infections. Alexander then tested the mold and found that it not only killed Staphylococcus, but also other bacteria including Streptococcus, Meningococcus and Diphtheria bacillus. Alexander Fleming's discovery gave mankind another, and highly effective, option to treat an infection while not killing the host.

Antibiotics Vs. Bacteria

Antibiotics are effective against bacterial infection and work against illnesses such as strep throat, bladder infections, and skin infections. However, antibiotics only work against bacteria. They have no effect on viruses such as influenza, gastroenteritis, or even the common cold or cough. Antibiotics kill and stop the growth of bacteria, but not all antibiotics work on all bacteria and the method they use varies.

Bacteria are divided into two types based on the structure of their cell: gram-positive and gram-negative. Gram-positive bacteria have a thin single layer cell wall that is easily permeable such as Streptococcus. Gram-negative bacteria have a thicker two-layer cell wall that is more difficult to penetrate such as E. coli. Antibiotics must be able to penetrate the cell wall to be able to stop the bacteria and effectively treat an infection.

Categorizing Antibiotics

Antibiotics fall into one of two categories: broad spectrum or narrow spectrum. Most antibiotics today are broad spectrum antibiotics which means they work against a wide range of different bacteria, for example, amoxicillin, gentamicin, and tetracycline. Narrow spectrum antibiotics work against a specific group of bacteria that is either gram-positive or gram-negative, but not both, such as penicillin.

How Antibiotics Work

Antibiotics generally stop bacteria by either: stopping a vital cell process, weakening the cell wall of the bacteria, or stopping the bacteria from multiplying. Beta-lactam antibiotics work by stopping the process of bacteria linking together molecules to create a cell wall. When the cell wall is destroyed, everything contained inside falls out and cannot live.

Macrolides are protein synthesis inhibitor antibiotics. They target the cell's ribosomes, the protein building center of the cell, and stop the metabolic process causing the cell to eventually breakdown. Both bacteria and human cells have ribosomes, but they differ in their structure. Macrolides work to only stop the process in bacterial cells. Proteins are the main working units behind a cell, so without protein a cell cannot function and dies. Erythromycin is a type of macrolide that is often used to treat skin and respiratory tract infections.

Quinolones are a type of broad-spectrum antibiotic that is effective against bacteria containing hydroxyl radicals. Quinolones work by destroying the lipids and proteins that make up the cell wall of bacteria as well as damaging the cell's DNA which prevents the bacteria from multiplying and spreading. Ciprofloxacin and levofloxacin are quinolones that are used to treat bronchitis and pneumonia.

Antibiotics work by targeting the weaknesses of bacterial cells and destroying them, while at the same time not harming human cells. For example, human cells are not contained inside of a cell wall like many types of bacteria. Human cell membranes, the part responsible for copying DNA and cell reproduction, differ from the structure of bacteria.

When antibiotics enter the bloodstream they do not harm human cells, they only kill bacteria. This is good as they will stop the bacteria causing the infection. Unfortunately, there are lots of types of friendly bacteria in the human body that actually keep the body healthy and help it function. Antibiotics kill all bacteria, both friendly and harmful. The loss of friendly bacteria actually leads to the increased growth of harmful bacteria that the friendly bacteria was once inhibiting. This can lead to opportunistic infections when antibiotics throw off the balance of bacteria contained in a body.
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