Types Of Antibiotics: 6 Unique Important Types



Antibiotics are medicines that possess killing bacteria properties or can stop them from growing.

They treat infections caused by bacteria, such as certain types of pneumonia, urinary tract infections, and strep throat. 

These drugs will not kill viruses, so they are of no use against viral illnesses like colds or the flu.Types Of Antibiotics



Scottish doctor physician Alexander Fleming (1881–1955) discovered the first antibiotic, penicillin, in 1928.

Since then, several types of antibiotics have been introduced. These drugs treat different kinds of bacteria.

Bacteria can be gram-positive or gram-negative, depending on the makeup of their cell walls.

Gram-negative bacteria have a thin outer membrane that is hard to penetrate. Examples include Escherichia coli(E. coli), which causes foodborne illnesses, and Klebsiella pneumoniae, which causes pneumonia, urinary tract infections, and bloodstream infections.

Gram-positive bacteria have a thicker membrane. Examples include Staphylococcus aureus, which causes staph infections, and Streptococcus causes strep throat, meningitis, and other infections.

Doctors use a Gram stain test to distinguish Gram-positive from Gram-negative bacteria. On this test, Gram-positive bacteria turn purple.

Gram-negative bacteria turn red. Testing a sample of bacteria can help determine which antibiotics will work best against the type of infection you have.

The main classes of types of antibiotics are:

  • Beta-lactams such as penicillin, amoxicillin, and cephalosporins are broad-spectrum, meaning they work against Gram-positive and Gram-negative bacteria. Doctors prescribe them to treat skin infections, urinary tract infections, sinus infections, and lung infections.
  • Tetracyclines such as doxycycline (Vibramycin) and tetracycline (Sumycin) are also a broad spectrum. They treat a wide number of infections, as well as acne.
  • Macrolides are among the most commonly used antibiotics. They include erythromycin (Ery-tab, Erygel), azithromycin (Zithromax), and clarithromycin (Biaxin) and are used to treat respiratory infections such as pneumonia. They are also useful in people who are allergic to penicillin.
  • Fluoroquinolones such as ciprofloxacin (Cipro) and ofloxacin (Floxin) are broad-spectrum and are used to treat various bacterial infections.
  • Aminoglycosides such as gentamicin (Garamycin) and tobramycin (Tobrex) are mainly used to treat serious infections caused by Gram-negative bacteria. They can sometimes cause serious side effects, such as kidney damage and hearing loss.
  • Sulfonamides such as co-trimoxazole (Bactrim) and sulfasalazine (Azulfidine) are less used today because many bacteria have become resistant to them.

To treat bacterial infections like pneumonia or strep throat, you will likely take antibiotics by mouth as tablets, capsules, or a liquid.

Antibiotic creams or sprays treat skin infections. If you face a very severe infection, you may need to get stronger antibiotics at a hospital through a vein in your arm (IV).


Doctors prescribe antibiotics for infections that are caused by bacteria, such as:

  • strep throat
  • urinary tract infections
  • whooping cough
  • some cases of bronchitis
  • some sinus infections

Antibiotics will not work against these illnesses, which are caused by viruses:

  • colds
  • flu
  • some ear infections
  • most coughs and sore throats
  • most sinus infections
  • most cases of bronchitis
  • stomach viruses

To find out if you have a bacterial infection, your doctor will first ask about your symptoms. Taking a culture can help the doctor determine whether bacteria caused the infection and which kind of bacteria.

The doctor will take a swab of body fluid and send it to a lab for testing. For example, a throat culture removes a fluid sample from the back of your throat to test for strep throat.

In a laboratory, the sample is placed in a substance that encourages bacteria to grow. If bacteria do grow, then you have an infection that may be treatable with antibiotics.

Doing a culture can also let your doctor know which types of antibiotics might be most effective based on the type of bacteria causing your infection.

Doctors may be more likely to prescribe antibiotics if an infection does not clear up on its own within a week or if it could cause severe complications.

People who are at high risk for catching an infection may take antibiotics to prevent it. This is called prophylaxis.


Follow the dosing instructions carefully when taking antibiotics. Do not skip any doses. Finish the entire course of medicine your doctor prescribed, even if you start feeling better.

If you do not complete all the medicine, some bacteria could remain alive in your body and make you sick again.

It is important not to share, overuse, or misuse antibiotics because it can lead to bacterial resistance. About 30 percent of antibiotics in the United States are prescribed unnecessarily for viruses and other infections they cannot treat.

Misusing these drugs can contribute to the problem of drug-resistant bacteria. Sometimes after being exposed to antibiotics, certain germs develop traits that help them resist these drugs.

The stronger germs then multiply and pass their protective traits on to the next generation of bacteria. Eventually, many bacteria can become immune to the effects of the antibiotic.

When those bacteria are exposed to the same antibiotics in the future, they cannot kill them.

Drug-resistant bacteria are tough to treat, and they can cause life-threatening infections. Bacteria such as Staphylococcus aureus (MRSA) and Clostridium difficile are resistant to many different antibiotics.

These bacteria can go from person to person and cause serious infections. According to the Centers for Disease Control and Prevention (CDC), each year in the United States, about two million people get infected with antibiotic-resistant bacteria, and 23,000 people die, according to the Centers for Disease Control and Prevention (CDC).

To avoid antibiotic overuse, do not ask your doctor for these medications unless you are sure you have a bacterial infection.

Practice good handwashing, get adequate rest and nutrition, and get recommended immunizations to reduce your chances of acquiring a bacterial infection that requires antibiotics.


Antibiotics, like many other types of medicines, can cause side effects. If you take them when you do not need them, you could have side effects without getting any benefit.

Potential antibiotic side effects include:

  • dizziness
  • nausea
  • diarrhea
  • allergic reactions
  • yeast infections

Antibiotics may also reduce the effectiveness of other drugs you take, such as birth control pills.

Because antibiotics kill all bacteria, including the healthy bacteria that live in your digestive and reproductive tracts, they can cause side effects such as upset stomach and vaginal infections.


“Antibiotics.” NHS. September 27, 2018. https://www.nhsinform.scot/tests-and-treatments/medicines-and-medical-aids/types-of-medicine/antibiotics (accessed October 21, 2018).

“Antibiotics: When They Can and Can’t Help.” American Academy of Family Physicians. July 10, 2017. https://familydoctor.org/antibiotic-resistance/?adfree=true (accessed October 21, 2018).

“What Everyone Should Know.” Centers for Disease Control and Prevention. May 29, 2018. https://www.cdc.gov/antibiotic-use/community/about/should-know.html (accessed October 21, 2018).