MRSA and other 'superbugs'

We sometimes hear about health scares involving so-called superbugs such as MRSA, Clostridium and E.coli, but what are they and how do they develop?

Superbugs are bacteria resistant to almost all antibiotics. Since the first antibiotic, Penicillin, was discovered in 1928, several different types of the medicine have been developed which work in two main ways:

• By making bacterial cell walls leaky, so bacteria absorb excess water and burst (penicillins and cephalosporins)
• By interfering with protein production so bacteria fail to grow or reproduce (tetracyclines, macrolides, aminoglycosides)

Bacteria are among the most primitive life forms on the planet, and reproduce when their cells divide to form two identical clones. The way their genes are copied is unsophisticated, and errors regularly occur. Some of these mutations make the bacterium resistant to certain antibiotics.

This may occur by secreting an enzyme that destroys the antibiotic, or by changing its metabolism to bypass the antibiotic's action. This resistance is most likely to develop when bacteria are exposed to low, sub-lethal doses of antibiotic, when antibiotics are used inappropriately (to treat a viral cold, for example) or when a course of antibiotics is stopped too soon.

Antibiotic resistance is most likely to develop in the most primitive parts of bacterial genetic material, known as plasmids. These are separate from the main bacterial genes and bacteria readily swap these plasmids among themselves.