Antibacterialsbrought to you by Elizabeth Warren


While this may come across as stating the obvious, a bacterial infection is one formed by a parasitic growth of single-celled microorganisms – bacteria - in the body. Unlike a virus, which must attach to a living cell in order to survive and reproduce, bacteria are independent, living cells. As the bacteria do not intertwine with a human cell to reproduce, drugs known as antibacterials are able to target the disease cells without harming other cells in the body. Antibacterials, also called antibiotics, are used to treat a wide range of bacterial diseases including but not limited to:
  • Tetanus
    Picture 1
  • Cholera
  • Typhoid Fever
  • Chlamydia
  • Streptococcus (Strep throat)
  • E-coli
  • Staphylococcus (Staph infections)
  • Bacterial Meningitis
  • Tuberculosis
  • Syphilis

Antibiotics work with the body's white blood cells, weakening the bacteria and not allowing it to reproduce. This gives the white blood cells a chance to kill the infection without being overwhelmed by its numbers.

Early Antibacterials

The earliest antibacterial drugs are a group called the sulfonamides, which had a high success rate at treating septicemia. Septicemia, often referred to as a septic infection, is an extremely dangerous infection which begins in any given part of the body and spreads rapidly, becoming deadly. Sulfonamide drugs were efficacious in lowering the death rate of patients with septic infections. However, despite the wonderful effects that the drugs were producing, biologists and doctors didn't know why they were happening. In the early days, antibiotics were a happy mystery.


Penicillin comes from the mold Penicillium notatum, and is the most common and widely used antibiotic in current medicine. It is a narrow-spectrum antibiotic, meaning it targets only specific types of bacteria, and is commonly used to treat many types of bacterial problems, from ear-infections to infected wounds.


Penicillin G, the form found in the Penicillium notatum mold is structured as shown below. The most integral piece of the penicillin structure is the beta-lactam ring. This ring contains three carbons atoms and a nitrogen atom, and is the piece of the molecule that gives it its antibacterial properties.

Picture 2 - The basic structure of penicillin. Note the beta-lactam ring, circled in red.
Picture 3


Penicillin functions by preventing the bacterial enzyme from forming links within its cell walls. In doing so, it weakens the cell walls, causing them to break down, and the bacteria cells die while trying to reproduce. This allows the body’s natural defense system – white blood cells – to fight the bacteria without the number of bacteria cells increasing. The body can quickly kill off the harmful cells once they are not reproducing.

Follow this link to see a time-elapsed video of bacteria bursting due to penicillin:


Penicillin G can be broken down by the digestive system, and is therefore only administered through intravenous injection. However, alternative structures of penicillin exist with different side chains (see below). These changes allow the antibiotic to be taken as a pill and still be effective. 

Picture 4 - A structure of penicillin that is not broken down by stomach acid. This is possible because of the different side chain, circled above.


The side effects of penicillin are rare and usually mild, and include nausea, exaggerated reflexes, and/or pain and swelling at the injection site. Some patients have severe allergic reactions to penicillin. These allergic reactions can be immediate, or can be caused by long and repeated exposure to the antibiotic. 

Narrow-Spectrum vs. Broad Spectrum

The antibiotics discussed so far, sulfonamides and penicillin, are narrow-spectrum antibiotics, meaning that they are effective against only certain types of bacteria. Broad-spectrum antibiotics, on the other hand, are effective against a much wider range of bacteria. Both have their uses, and both have advantages and disadvantages.

Comparison Table

Broad-Spectrum Antibiotics
Narrow-Spectrum Antibiotics
  • Used to treat bacterial infections when the pathogen is unknown or cannot be identified due to time constraints.
  • Used when multiple types of bacteria infect the body at the same time. (e.g. meningitis)
  • Used to treat a specific, known bacteria.
  • Treats many different types of bacterial infections.
  • Effective against more than one pathogen at the same time.
  • Less need to identify the specific pathogen. (This makes it possible to treat immediately with antibiotics in an emergency situation.)
  • Does not affect beneficial bacteria such as that in the digestive tract.
  • Leaves human cells untouched.
  • Use increases the likelihood of producing a drug-resistant bacteria.
  • Kills off beneficial bacteria as well as parasitic bacteria (e.g. bacteria in the digestive system)
  • The specific bacteria must be identified to be treated with narrow-spectrum antibiotics
  • Must be used to completion to ensure that there are no surviving bacteria.
  • Amoxcillin
  • Levofloxacin
  • Sulfonamides
  • Penicillin


In recent years, a problem with over-prescription has developed regarding penicillin and other antibiotics. Mutations in bacterial strains have lead to bacteria which produce an enzyme known as penicillinase, which targets and breaks the beta-lactam ring in penicillin (see above), and inhibits its activity. These mutations are caused by over-use of antibiotics to treat infection. After prolonged exposure to an antibiotic, any bacteria that may have survived are able to reproduce, giving the next generation of bacteria resistance to the antibacterial.
Picture 5 - Penicillinase - the enzyme that attacks the beta-lactam ring, rendering penicillin useless.
Picture 6

There are a few methods in place to control the over-prescription of antibiotics:

  • Legislation to make antibiotics prescription-only drugs, which limits their availability when they are not necessary.
  • Education of patients to take all the doses of antibiotics prescribed to them to ensure that the medication kills all harmful bacteria, leaving none to reproduce and form a resistant strain.
  • The research and production of other forms of penicillin that can resist the harmful action of penicillinase.

Picture 7 - Coxacillin Sodium - an antibiotic that resists the enzyme penicillinase.

Bet you didn't know: In addition to being over-used by humans directly, antibiotics are introduced into the human system through livestock. Antibiotics are frequently added to the animals’ regular feed to prevent typical diseases. When such animals are ingested, the antibiotic is distributed in the human bloodstream, causing even more exposure to common antibiotics, exacerbating the problem of over-use.

A Little Bit of History

In 1928 Alexander Fleming was performing an experiment with bacterial cultures, and noticed that a common mold called Penicillium notatum was growing in his Petri dishes. All around the mold were clear places with no bacteria. Possibly one of the most famed accidental discoveries in medical history, this event led to research by Howard Florey and Ernst Chain in 1940. They managed to extract the antibacterial within the mold – penicillin. They then began to test its capabilities as a treatment for bacterial infections. It was first tested on humans in 1941 – right in the middle of World War II. It was an amazing success, and it led to the drug’s extraordinarily fast development and distribution. For the first time, doctors in the field were able to treat the bacterial infections caused by war injuries. The drug proved to be invaluable – saving thousands of soldiers’ lives in the main years of the war. The discovery of penicillin earned Fleming, Chain, and Florey a joint Nobel Prize in Medicine.

Picture 8



  • SRS Pharmaceuticals
  • Chemistry, 3rd Edition, by John Green and Sadru Damji (p. 422 - 424)
  • (Pearson Baccalaureate) Higher Level Chemistry, by Catrin Brown and Mike Ford (p. 644 - 646)

Pictures (see numbers in captions)