How and why does antibiotic resistance emerge?

Each time that antibiotics are used, the subset of bacteria able to endure their onslaught not only survive but can make the most of the elimination of susceptible bacteria around them to thrive.

Antibiotic resistance is a natural phenomenon which has been around for millions of years. Indeed, bacteria and fungi produce antibiotics naturally, to protect themselves or to fight each other. The first antibiotics used in medicine, including penicillin, were extracted from fungi. However, the use of large quantities of such substances in human and animal health care since the mid-1940s has greatly amplified a natural process: each time that an antibiotic is used, resistant bacteria multiply and then prosper because they are the only ones able to do so under those particular circumstances.

When bacteria multiply – most are able to do this several times per hour – they must replicate all their genes (DNA). As these copies are made, the bacteria are also subject to errors (mutations), some of which might help them survive the onslaught of an antibiotic in their surroundings. They can also acquire this ability by receiving small pieces of DNA (plasmids) from other bacteria – which may or not be of the same species.

How do bacteria resist antibiotics?

Bacteria can resist antibiotics in several ways:

By ejecting the antibiotic out of the cell
By making their membrane impermeable for the antibiotic
By modifying the antibiotic chemically, to deactivate it
By modifying the proteins in the cell that are targeted by the antibiotic.

Perhaps the most worrying aspect of the expanding problem of antibiotic resistance – which is advancing world-wide – is the accumulation of several forms of resistance in the same disease-causing bacteria. These multi-resistant bacteria are able to grow normally even when they are treated by several classes of antibiotic at the same time. Some are even able to resist all known antibiotics.