Antibiotic action on bacterium. Illustration of an antibiotic drug acting on a bacterium, causing it to burst (lysis) and lose its DNA. The rod- shaped bacterial cell is coloured blue; the cell wall has lost its shape due to damage by the drug. Inside the cell is the nuclear envelope (purple structure). This has also ruptured due to drug action, causing the chromosome material (purple strands) containing DNA to burst from the cell. The uncoiling of the DNA prevents the bacterium from dividing before it dies. Antibiotic drugs are used to treat bacterial infections. Penicillin and cephalosporin antibiotics destroy bacterial cells in this way.