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1. Aerobic Non-Spore Forming Gram-Positive Bacilli Corynebacterium
3. Corynebacterium spp Gram positive bacilli, with characteristic morphology (club shaped and beaded)
Non spore forming
Breakdown glucose by oxidative and fermentative i.e. O+/F+
C. diphtheriae is fastidious while diphtheriods are non-fastidious
4. Species of Corynebacteria
8. Specimen: A throat swap
Culture: The swap is inoculated on Loeffler's serum medium and/or on blood tellurite agar aerobically at 37C for 24.
On Loeffler's serum medium:
Corynebacteria grow much more readily than other respiratory pathogens
Used to enhance the characteristic microscopical appearance of corynebacteria
The colonies of C. diphtheriae are small, granular, grey, smooth, and creamy with irregular edges
9. Cultural characteristics On blood tellurite agar (Mcloed’s blood agar)
It is selective medium for isolation of C. diphtheriae (Potassium tellurite)
3 biotypes of C. diphtheriae are characterized on BTA
i.e. Gravis, mitis and intermedius biotypes
The most severe disease is associated with the gravis biotype
Colony of gravis biotype is large, non-hemolytic & grey.
Colonies of mitis biotype are small, hemolytic and black
Colonies of intemedius biotype are intermediate in size, non-hemolytic with black center & grey margin.
Gram +ve, nonspore forming nonmotile bacilli
Club-shaped (Coryne= club) arranged at acute angles or parallel to each other (Chinese letters appearance)
Beaded (metachromatic granules)
C. diphteriae are gram positive bacilli arranged in Chinese letters form often club shaped
Polychrome methylene blue stain:
C. diphteriae appears beaded due to the presence of intercellular “Metachromatic or volutin" granules
By stain, the granules appear red while the rest of organism appears blue.
12. Biochemical Reaction All Corynebacterium species are catalase positive (Also, Staphylococcus and Bacillus species are catalase positive)
17. In Vitro: Elek’s Test Principle:
It is toxin/antitoxin reaction
Toxin production by C.diphtheriae can be demonstrated by a precipitation between exotoxin and diphtheria antitoxin
A strip of filter paper impregnated with diphtheria antitoxin is placed on the surface of serum agar
The organism is streaked at right angels to the filter paper
Incubate the plate at 37C for 24 hrs
After 48 hrs incubation, the antitoxin diffusing from filter paper strip and the toxigenic strains produce exotoxin, which diffuses and resulted in lines four precipitation lines radiating from intersection of the strip and the growth of organism