Falsecolour transmission electron micrograph (TEM) showing the effect of an antibiotic on the bacterium Staphylococcus aureus. On the left are the remains of a bacterium destroyed by lysis (bursting); the bacterium at right is, as yet, undamaged and is in the process of dividing. Lysis is achieved by the destruction of the outer cell wall and the subsequent release of the intracellular contents into the surrounding medium. S. aureus is a Grampositive species of bacteria that is the commonest cause of pyogenic (pusforming) infections in humans. It has evolved a number of variants resistant to antibiotics. Magnification: x37,000 at 6x7cm size.