Anaerobic bacteria survive and grow in environments with little or no oxygen and include strains that cause botulism and tetanus. This article is an overview of the types of anaerobic bacteria, followed by a few examples.
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Types of Anaerobic Bacteria
There are three different types of anaerobic bacteria: -
Facultative anaerobes - these are bacteria that are capable of growing in the absence of oxygen. Their energy comes from fermentation. But if oxygen is present they can derive their energy by aerobic respiration.
Obligate anaerobes - need environments where there is no oxygen as they cannot grow in its presence. Some obligate anaerobes are even harmed by oxygen.
Aerotolerant bacteria - do not need oxygen to grow, but can survive in its presence.
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Examples of Anaerobic Bacteria.
Escherichia coli - a facultative anaerobe - named after its discoverer Theodor Escherich. E. coli is a common type of bacterium and most strains are harmless - indeed many are beneficial. They can be found in the intestinal tract of birds, humans and other mammals. Of those strains that can make you sick some cause diarrhea, while others can cause respiratory problems and urinary tract infections. Probably the most notorious types of E.coli are those that produce Shiga toxin, in particular the strain known as E. coli 0157: H7. The shiga toxin it produces is one of the most potent poisons we know about. In the 1980s an outbreak of E. coli 0157: H7 was traced to contaminated hamburgers. Since then, many cases of found poisoning by E.coli are believed to have come from undercooked beef.
Staphylococcusgenus- a facultative anaerobe- many strains are harmless and reside on human skin or mucous membranes. Under the microscope they look round (cocci) in shape. There are a number of strains that can cause infections, either by invading cells or releasing a toxin. One type that has been causing concern is Staphylococcus aureus, especially methicillin resistant Staphylococcus aureus (MRSA) which is resistant to a wide array of antibiotics and can cause a number of infections.
Clostridium genus - obligate anaerobes - under the microscope they appear rod-shaped. Examples include - 1) C. botulinum which produces the world's deadliest toxin- botulinum. The bacterium is commonly found in improperly handled meats. Botulinum in small quantities is used in medication to treat muscle spasms, and in cosmetics to lessen the appearance of wrinkles 2) C. tetani which causes tetanus and 3) C. perfringens which is found in decaying vegetation and in the human intestinal tract. Infections with the bacterium can cause tissue necrosis and gas gangrene.
Bacteroides - some species are beneficial to humans as they crowd out potential pathogens. They form a considerable part of the normal human flora. As such many strains are opportunistic human pathogens, and can cause infections in several parts of the body including the peritoneal cavity and the female urogenital tract.