How Do Antibiotics Work?
Scottish physician Alexander Fleming discovered the first antibiotic, penicillin, in 1928. Antibiotics were then introduced to the public in the 1940s. Prior to this, there were very few options for treating bacterial infections. Most involved either cutting away the infected part of your body or waiting for the infection to subside on its own. Even the most minor of infections could be fatal.
Today, antibiotics are a mainstay of medicine, helping your immune system battle all sorts of bacterial infections. However, there are still some misconceptions about antibiotics. Read on to learn about antibiotics and how they work in your body.
What are Antibiotics?
Antibiotics refer to a variety of medications designed to neutralize bacteria. Antibiotics usually come in the form of pills or capsules to be ingested orally, but they can also be injected by needle or applied directly to the affected area via topical cream.
The type of bacteria causing your infection determines the type of antibiotics that your doctor prescribes. Most bacteria are divided into two groups: gram-negative and gram-positive. These classifiers are mainly just based on the type of cell wall that a bacterium has.
Gram-negative bacteria, which includes E. coli, have thick, two-layered cell walls that are difficult to penetrate. Streptococcus and other gram-positive bacteria have single-layered cell walls, which are thin and easily permeable. For antibiotics to be effective, they need to find a way to break through these cell walls.
Broad and Narrow Antibiotic Spectrums
The mechanism of action varies from antibiotic to antibiotic, but most work by:
- Killing the bacteria outright by weakening its cell walls until it bursts
- Inhibiting a bacteria’s ability to grow, multiply, and spread
- Blocking vital processes that allow the bacteria to repair any damage to its DNA
Antibiotics are also divided into two groups. Broad spectrum antibiotics affect a variety of different bacteria and include gentamicin, amoxicillin, and levofloxacin. Most antibiotics are broad spectrum and can affect both gram-positive and gram-negative bacteria. Narrow spectrum antibiotics, which include penicillin and azithromycin, are only effective on a few specific bacteria, either gram-positive or gram-negative but never both.
Let’s Get Technical - Breaking Down the Biology of Antibiotics
For example, as a narrow spectrum antibiotic, penicillin destroys a bacteria’s cell wall, which is what keeps the bacteria together. Glycopeptide antibiotics prevent gram-positive bacteria from repairing or building new walls. Specifically, these antibiotics inhibit the production of peptidoglycan, a molecule in the cell wall that gives the bacteria the strength to survive in the human body.
On the other hand, quinolones are a broad spectrum antibiotic that uses hydroxyl radicals to eliminate bacteria. Hydroxyl radicals are molecules that cause damage to the various protein and lipid building blocks comprising the cell’s membrane.
Hydroxyl radicals also do direct damage to a cell’s DNA by targeting DNA gyrase. DNA gyrase is an essential enzyme that is involved in the process of unwinding DNA to replicate bacterial cells. By eliminating DNA gyrase, quinolones like ciprofloxacin prevent bacteria from replicating and spreading.
Antibiotics Eliminate Bacteria Inside Out
While many antibiotics work from outside a bacteria’s cell walls and break in, others work to eliminate bacteria from the inside out. For example, macrolide antibiotics specifically inhibit protein synthesis.
Let’s Get Technical - Breaking Down the Biology of Antibiotics
Erythromycin, a common macrolide, binds to certain molecules in a bacteria’s ribosomes. This prevents the cells from being able to form the proteins and other resources they need for continued growth. Tetracycline, which is an antibiotic commonly prescribed for acne and respiratory tract infections, is also a protein synthesis inhibitor that works in the same way.
Rifamycin, a family of antibiotics often prescribed for tuberculosis, works by inhibiting a bacteria’s ability to synthesize RNA, which is the molecule that translates DNA into proteins. While the method is different, the results are essentially the same.
Other antibiotics work by preventing bacteria from producing folic acid, a vitamin that is necessary to their survival. Still others compromise the structure of bacterial cell membranes, interrupting how substances move into and out of the bacteria.
Bacteria vs. Viruses: What’s the Difference?
One of the most important things to remember about antibiotics is that they are only effective against bacteria. While bacteria and viruses are responsible for a wide range of diseases, they are significantly different organisms.
Bacteria are single-celled organisms and can live in a variety of different settings. Some can even survive extreme temperatures, while others take root in human intestines and help you digest your food. Your body is filled with thousands of bacteria, and most of them are completely harmless.
However, invading bacteria can enter your body and cause illnesses. Common bacterial infections include:
- Strep throat
- Certain sinus infections
- Urinary tract infections
- Kidney infections
- Whooping coughs
Viruses are much smaller than bacteria, and they can only exist with a living host, whether it’s a person, animal, or plant. They otherwise cannot survive. When a virus finds its way into your body, it invades certain cells and rewrites how those cells operate, forcing them to produce more viruses. Some common diseases caused by viral infections include the common cold and flu, stomach flu, chickenpox, and AIDS.
It’s important to use antibiotics only if you are suffering from a bacterial infection, but that can often be difficult. Many illnesses and symptoms can be caused by either bacteria or viruses. These include diarrhea, meningitis, and pneumonia.
Side Effects of Antibiotics
Antibiotics can cause side effects based on how they work. Antibiotics are designed to kill bacteria. That usually means that they attack foreign bacteria that hurt you, but antibiotics can also kill the good bacteria that help your body’s basic processes. This can potentially lead to side effects. The most common side effects of antibiotics include:
- Upset stomach
- Thrush, which is a fungal infection that can affect the mouth or digestive tract
- Vaginal yeast infection (discharge, burning, pain, itchiness)
In rare instances, you may suffer an intestinal infection that can lead to ongoing diarrhea and more serious symptoms. You may also be allergic to certain antibiotics, leading to an allergic reaction that can include:
- Breathing issues
- Swelling in your tongue and face
One of the biggest problems that comes with antibiotics is overusing them. According to the CDC, 68 percent of patients with acute respiratory tract infections are prescribed antibiotics, but only about 20 percent of them actually need antibiotics. While overusing antibiotics or taking them when you do not need them can lead to side effects, the more significant problem is bacteria that is actually resistant to bacteria.
Overusing antibiotics or not finishing your antibiotics as prescribed can actually lead to bacteria picking up habits and traits that allow them to fight against this medication. They can acquire resistance by getting a resistance gene encoded to its chromosomes. This can happen in a few ways:
- Transformation – In this process, bacteria join together and exchange DNA with each other.
- Plasmids – Bacteria can pick up free-floating plasmids, a small, extra-chromosomal piece of DNA. These plasmids encode resistance to different antibiotics.
- Transposon – Known as “jumping genes,” transposons are small pieces of DNA that can jump from one DNA molecule to another.
Once these bacteria gain a resistance gene, they can keep antibiotics from working through various mechanisms:
- Change the target – Antibiotics work by targeting specific bacteria and preventing it from interacting with certain molecules, but some resistant bacteria can change the structure of the target or replace it with a different molecule altogether. This prevents the antibiotic from recognizing or even binding to the bacteria.
- Keeping the antibiotic away from its target – Some resistant bacteria change the permeability of their membranes or otherwise reduce the number of channels that drugs can diffuse into. Some bacteria use ATP to fuel pumps that forcefully remove antibiotics from the cell.
- Eliminating the antibiotic – Some bacteria interfere with antibiotics to the extreme. Instead of setting up walls or pushing the drug away, some bacteria will kill antibiotics directly through various means. For instance, some bacteria learn to secrete enzymes known as beta-lactamases, which can actively eat up penicillin.
How to Take Antibiotics
The best way to take your antibiotics is to follow your doctor’s instructions. Make sure you take the dose as your doctor prescribes and at the proper time. Most antibiotics are taken on an empty stomach, meaning an hour before a meal or two hours after a meal.
Antibiotics are effective, sometimes surprisingly so. They can take effect within the first few hours of administration, and most people will feel significantly better within the first day. Regardless of how you feel, make sure you complete the full course of antibiotics as prescribed by your doctor to completely eliminate the invading bacteria from your body.
If you stop early, you may still have bacteria in your body. These can potentially grow and re-infect your system. Worse yet, they may become resistant to the antibiotic.
On the other hand, some antibiotics take longer to work than others. If you do not feel better within the first few days after taking antibiotics, do not take more of your antibiotic. Instead, consult your doctor. Taking a higher dosage than you were prescribed may just cause greater side effects and contribute to higher chances of creating resistant bacteria.
Make sure you inform your doctor of other prescription medications that you are taking as the antibiotics may affect how well the other medications work. For example, some antibiotics can affect birth control effectiveness.
Some antibiotic boxes contain more pills than you were prescribed. Do not keep unused antibiotics, and definitely do not share antibiotics with others.
How to Get Antibiotics
Antibiotics can (and should) only be prescribed by a doctor. The process will generally start with a physical exam. Your doctor will also ask about your personal medical history along with any symptoms you may have experienced.
Your doctor may have enough information from that to prescribe antibiotics, but if not, they will order lab tests that will allow them to properly identify the bacteria and provide a prescription.