The genus Corynebacterium consists of procaryotic bacteria that are true bacteria and heterotrophic. Human and animal pathogens, plant pathogens, and non-pathogens are the three different types of corynebacteria. Each type has its own characterisitics. Human and animal pathogens are generally non-motile and mostly anaerobic. They are Gram positive and have slightly curved rods with irregular segments. Snapping division causes a picket fence arrangement of the rods that is a notable characteristic of this type. The most notable pathogen is Corynebacterium diphtheria. Isolated on blood tellurite agar (e.g. Tinsdale Medium), Corynebacterium grows well on blood agar with the addition of potassium tellurite, which inhibits the growth of normal flora in the throat. Corynebacterium colonies turn a distinctive grey-black: tellurite diffuses into the bacterial cells and is reduced to tellurium metal which precipitates within the cell.
The picture to the left illustrates snapping division. The picture to the right is a wet mount (1,000X) showing club-shaped cells.
Plant pathogens have similiar characteristics to the human and animal pathogen type. Less snapping division occurs and some of the species in this group are motile. Organic growth facters are needed for growth of these types of corynebacteria. These bacteria are also strictly anaerobic.
The non-pathogenic class of corynebacteria are poorly described taxonomically. These bacteria are hard to differentiate between
species due to insufficient data. Non-pathogens can be easily confused with at least ten other genera of bacteria.
The genus Corynebacterium has so many species that over forty media have been developed for isolation and characterization. Species of this genus can be isolated from soil, air, water, blood, and even human skin. Corynebacteria that infect plants or animals or humans usually pathogenic strains. Several species of corynebacteria that grow on plants cause a variety of plant diseases. One Corynebacterium species causes a disease known as bacterial wilt which infects the seeds of soybeans. The plants become stunted,
bean pods are empty, and marginal necrosis of the lower leaves become evident. Tan spot of soybeans is another disease caused by the same species of Corynebacterium.
Another plant disease caused by Corynebacterium tritici is spike blight of wheat. This species also infects the seed of the wheat plant. Several diseases in humans are caused by species of Corynebacterium. A familiar disease, diptheria, is caused by Corynebacterium diphtheriae. This disease is usually contracted by exposure to aerosol droplets or through contaiminated water. Humans, especially children, can die from diptheria if the disease is not treated promptly.
The American Phytopathological Society. Compendium of Wheat Diseases. 2nd Ed. St. Paul, Minnesota. 1977.
Fuhrmann, J., Hartel, P., Sylvia, D., and Zubere, D. (1988). Principles and Applications of Soil Microbiology. New Jersey: Prentice Hall Inc.
Holt, John G. (1984). The Shorter Bergey's Manual of Determinative Bacteriology. 8th Ed. Maryland: The Williams and Wilkins Company.
Corynebacterium and Microbial Diversity.
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