Lactic acid bacteria. Coloured scanning electron micrograph (SEM) of Lactococcus sp. bacteria. Lactococcus are important in the production of fermented dairy products such as cheeses. They are gram-positive, mesophilic bacteria that break down sugar (glucose) into lactic acid (lactic fermentation), which in turn precipitates milk proteins so that thickening occurs. Magnification: x25000 when printed 10 centimetres wide.