Pectinatus is a genus of strictly anaerobic, Gram-negative, spherical bacteria of which some species are common contaminants of non-pasteurized, packaged beers. During the 1970s the processing and packaging of beers became more controlled and oxygen concentrations could be kept to an absolute minimum. This improved beer quality but unexpectedly opened the beer to a new bacterial threat: strictly anaerobic organisms that are killed by oxygen. First reported by S. Y. Lee and coworkers at Coors Brewery in 1978, these isolates from packaged beer were assigned to the genus pectinatus as Pectinatus cerevisiiphilus. They have since been encountered widely in Germany, Japan, and Scandinavia. Other species, Pectinatus frisingensis and Pectinatus haikarae, have since been described. Spoilage of packaged beer is evident from turbidity and off-flavors reminiscent of rotten eggs from the production of hydrogen sulfide. See hydrogen sulfide. Similar anaerobic bacteria isolated from finished beer in Germany in 1979 were classified in the genus megasphaera as Megasphaera cerevisiae. These bacteria are sensitive to ethanol and are therefore more common in low-alcohol products. A strain of a second species isolated from spoiled finished beer, Megasphaera sueciensis, was described in 2006. However, it seems that megasphaera strains are less common than pectinatus as beer contaminants. It should be emphasized that laboratory culture of these organisms requires attention to strict anaerobic techniques; they cannot grow in the presence of oxygen.

See also bacteria.