What are antibiotics?

Antibiotics – the basics

You may have heard both the terms “antimicrobial” and “antibiotic”.

Although often used interchangeably, they actually have distinct meanings:

• Antimicrobial: is any substance that kills or inhibits the growth of micro-organisms (e.g. bacteria, fungi, parasites, and virus).

• There are three types of antimicrobials that work against bacteria:

1. antiseptics (e.g. used to clean a wound to prevent infection)

2. disinfectants (e.g. used to clean a surface of bacteria)

3. antibiotics: any compound that kills or prevent the growth of bacteria and are taken internally as medicine or used topically (e.g. on the skin or in the eye).

Where do antibiotics come from?

For thousands of years humans have used various substances to prevent or treat infections including plants, bread mould and honey.

In the late 19th century, scientists discovered that bacteria cells could be stained by chemical dyes. This led scientists to start looking for compounds that would kill pathogenic bacteria.

The first antibiotic to be discovered was arsphenamine (Salvarsan), which was discovered in 1909 by Paul Ehrlich and Sahachirō Hata. This was the first effective treatment for the sexually transmitted infection syphilis (caused by Treponema pallidum).

This was followed in 1932 by the discovery of Prontosil by a team led by Gerhard Domagk, who were systemically testing chemical dyes for their ability to kill bacteria. Prontosil is a sulfonamide antibiotic, which is effective against a number of different pathogenic bacteria and is still in use today.

Despite these successes, if you ask people to name an antibiotic today, the vast majority will say “penicillin”. The reason for this – penicillin was the first antibiotic to be discovered that will kill many types of bacteria (known as a broad spectrum antibiotic).

While the first two antibiotics to be put into clinical usage were synthetic compounds, penicillin came from another living organism (Penicillium chrysogenum).

In 1928 Alexander Fleming found that a fungus called Penicillium chrysogenum produced a compound that could kill the bacterial pathogen Staphylococcus aureus. Fleming named the compound “penicillin” – and found that even at very low concentrations penicillin could kill a number of bacterial pathogens. Although Fleming made the initial discovery, he was unable to take it any further.

The story of penicillin restarted during the second world war at Oxford University. In 1940, Howard Flory assembled a team of researchers including Ernst Chain, Norman Heatley, Edward Abraham and others to work on penicillin.

They discovered the method required to extract penicillin in high enough concentrations to begin to test the effectiveness of penicillin against real infections. They first showed excellent activity of penicillin against bacterial infections in mice. They then moved on to conduct the first successful clinical trials in human patients.

Later researchers and pharmaceutical companies in the USA developed the methods to enable the industrial scale production of penicillin required for widespread clinical usage.

Following the success of penicillin, researchers began to search for other fungi and bacteria that produced antibiotics. As a result, in the 1950’s, 60’s and 70’s many new types of antibiotics were discovered and went into clinical use.

However, once we reached the 1990’s the pipeline of new antibiotics dried up.

Why do you think this happened?