Antibiotics 101: What are they and why do we need them?

Antibiotics are arguably one of the most important and impactful medical discoveries—they’ve revolutionized how we treat illness and saved countless lives from bacterial infection.

When were antibiotics invented?

In 1928, scientist Alexander Fleming accidentally discovered penicillin when he left a bacterial culture uncovered while away on vacation, according to Microbiology Society. A mold grew in his petri dishes, and killed the bacteria he was studying.

Fleming’s forgetfulness led to the first mass-produced antibiotic, or bacteria-killer, for which he won a Nobel Prize in Physiology or Medicine, along with two other scientists, in 1945.

What are antibiotics used to treat?

Antibiotics are life-saving medications prescribed to fight infections by killing bacteria or keeping it from reproducing, explains The National Library of Medicine’s MedlinePlus. While antibiotics are used to treat many serious bacterial infections, they are not required for—or effective on—viral infections, like the common cold or flu.

“Antibiotics are medications that are used to assist a patient’s immune system to combat bacterial infections,” Katie Taylor, Pharm.D., says. She adds that types of bacterial infections may include urinary tract infections, pneumonia, and skin and soft tissue infections, just to name a few.  

How do antibiotics work?

Antibiotics kill the bacterial cells causing your infection, but they leave human cells alone, explains The Genetic Science Learning Center at The University of Utah. 

According to Merck Manual, there are a wide variety of antibiotics available, and each type of antibiotic works on certain kinds of bacteria. This is why your doctor prescribes specific antibiotics to treat particular bacterial infections. There are many types, or classes, of antibiotics: penicillins, tetracyclines, and nitrofurantoin, just to name a few.

Within these classes, there are a variety of brands available.

Different kinds of “antibiotics work in a variety of different ways depending on the class of antibiotic they are,” says Amesh Adalja, MD, a board-certified physician in infectious diseases and senior scholar at John Hopkins. “For example, penicillin and related antibiotics disrupt bacterial cell wall structure, while antibiotics like ciprofloxacin act on bacterial DNA processes.”

There are also a variety of different forms of antibiotics. They can be taken orally, applied topically, or received as an injection. “One important factor to note is that not only does a particular antibiotic need to be able to kill a particular bacteria, but also get to the site of infection,” explains Dr. Taylor. “For example, not every antibiotic can get into the brain or into the bone, and if that is where the infection is, it will be difficult to treat that infection with that drug.” Your physician prescribes the form that can best target where the infection is in your body. 

How long does it take antibiotics to work?

Antibiotics kick in fairly quickly, at least at the microbiological level, explains Dr. Adalja. “However, depending on the extent and severity of the infection, it may take hours or days for a person’s symptoms to noticeably change,” he adds. 

When your symptoms start to improve, you shouldn’t stop taking your prescription. “It is important to stress that a patient should take the entire course of antibiotics prescribed by your healthcare provider to ensure adequate treatment of the infection so that it does not recur nor cause antibiotic resistance,” Dr. Taylor emphasizes.

RELATED: What happens if you don’t finish antibiotics?

How do bacteria become resistant to antibiotics?

Antibiotic resistance occurs when bacteria learn how to overcome the antibiotic that is supposed to kill them. It occurs when people overuse and underuse antibiotics. They take them for a condition that doesn’t require antibiotics, or they stop taking an antibiotic before the prescription ends. Both scenarios give bacteria the opportunity to mutate.

Antibiotic resistance is so common that the Centers for Disease Control and Prevention (CDC) consider it one of the most urgent public health crises. Every year more than 2 million people get an antibiotic-resistant infection, and at least 23,000 people die from it, according to the CDC. “Infections caused by antibiotic-resistant germs are difficult, and sometimes impossible, to treat. In most cases, antibiotic-resistant infections require extended hospital stays, additional follow-up doctor visits, and costly and toxic alternatives,” says the CDC site. 

Dr. Adalja says that while overuse of antibiotics can lead to antibiotic resistance, the bacteria’s ability to evolve and resist the medication designed to kill it is also a fact of life and evolution. “Antibiotic resistance is caused by a variety of factors, but generally is due to bacteria being exposed to an antibiotic for some time, and the bacteria mutating (or figuring out) how to get around the drug’s mechanism of action,” agrees Dr. Taylor.

When to take antibiotics

The best way to prevent antibiotic resistance is to avoid taking antibiotics when you don’t need to—for example, don’t take antibiotics to treat viruses. Use preventative measures like vaccines and healthy hygiene habits to avoid getting sick. Then, if you do need them, make sure that you take your antibiotics exactly as prescribed.