Illustration showing aztreonam (orange), an antibiotic, being broken down by the bacterial enzyme beta lactamase (blue). Aztreonam usually functions by inhibiting bacterial cell wall synthesis, which leads to the death of the bacteria. Some bacteria are resistant to aztreonam, however, as they contain beta lactamase. This enzyme hydrolyses (breaks down) a compound in aztreonam called beta lactam, inactivating the drug. The molecular structure of aztreonam (top left) is shown with atoms represented as spheres and colour-coded: carbon (grey), hydrogen (white), oxygen (red), hydrogen (blue) and sulphur (yellow).