Oral bacteria. Coloured scanning electron micrograph (SEM) of mixed oral bacteria attached to buccal cells (pink) from the cheek. The mouth contains a large number of bacteria, most of which are harmless or even beneficial. However, some bacteria can cause throat infections or cause the formation of plaque deposits on the teeth, which may lead to decay. A single red blood cell is present center left. Magnification: x4000 at 10cm high.