CORYNEBACTERIA

CORYNEBACTERIA (IRREGULAR)

The coryneform (irregular) group of Gram-positive bacteria includes several genera of non-spore-forming rods which are ubiquitous in nature. We will consider only two of these genera in our discussion of clinically significant microorganisms: Actinomyces and Corynebacterium. The first genus, Actinomyces, will be presented later when we focus on anaerobic Gram-positive bacteria.

(under the microscope)
The second genus, Corynebacterium, is comprised of facultatively anaerobic bacteria which are normaly saprophitic and harmless to humans. An exception is the bacterium C. diphtheriae which produces the toxin that causes diphtheria, a disease of the upper respiratory system in humans. Under the microscope (best viewed using Loeffler's methylene blue dye), C. diphtheria can be seen forming colonies which clump up or stick together. This is a characteristic associated with many higher forms of bacteria. Although other species of Corynebacterium can inhabit the mucous membrane, C.diphtheriae is unique in its exotoxin formation. Treatment for the disease usually consists of administration of an antitoxin with penicillin.

Catalase +
Nitrate +
Glucose fermentation
Non-motile