Antibiotic effect on bacterium. Coloured transmission electron micrograph of the effect of an antibiotic drug on the bacteria Salmonella typhimurium. The drug polymyxin B caused the outer membrane (blue) to form long surface projections. This is the early stage of lysis, the bursting of the cell wall and release of the cell contents, killing the bacterium. Polymyxin B is a broad spectrum antibiotic against Gram- negative bacteria. Salmonella typhimurium is a major cause of food poisoning in humans. The bacteria are transmitted in contaminated food, causing fever and diarrhoea. Magnification: x30,000 at 6x6cm size.