with out granules but in Chinese character arrangement
grey-black with paler periphery
Classic morphology with numerous granules and typical arrangement
Medium-sized,circular convex,glistening and black
Biochemical reaction: Acid production from a range of carbohydrate fermentation Typing: Serotyping by agglutination tests, phage typing and
bacteriocin typing have been used C.diphteriae foe epidemiologic studies
Toxin production: responsible for virulence; can be demonstrated by guinea pig inoculation or by gel precipitation test 1. Guinea pig inoculation: Inject suspension of the isolated strain of
C.diphteriae into diphteriaantitoxin. Death in 2-3 days of the unprotected animal two guinea pig,
2. Gel-precipitation (Elek) test: a filter paper strip previously immersed in diphteria antitoxin is incorporated into serum agar; the strain of C.diphteriae under investigation is then streaked onto the agar at right angles to the filter paper strip. Incubate at 37 0c for 1-2 days, and observe for lines of precipitation in the agar indicating toxin-antitoxin interaction.
Schick test: a skin test to demonstrate immunitydue to immunization or natural infection Method: Intradermal injection of toxin into the anterior aspect of one forearm and heat-inactivated toxin into the other.