MRSA (Methicillin-Resistant-Staphylococcus-Aureus)

This hospital superbug is a strain of the common Staphylococcus aureus bacterium. It often lives on the human body without causing harm but when the body’s defences are weakened, it may cause an infection.

Individually, the bacteria appear spherical (-coccus from the Greek kokkos, meaning ‘berry’ or ‘grain’), but they can arrange themselves in groups or colonies shaped like bunches of grapes (staphylo- from the Greek word staphyle, meaning ‘bunch of grapes’) and in laboratory culture appear yellowish (aureus from Latin meaning ‘golden’).

MRSA has developed a defence against penicillin-type antibiotics (it is methicillin-resistant). It produces an enzyme (called β-lactamase), which breaks down the crucial central structure of the drug, preventing it from killing the bacteria.