Corynebacterium

Corynebacterium

Gram positive rods
Spore forming
Non spore forming
Anaerobic
Aerobic
Clostridium spp
Bacillus spp
Corynebacterium
Gram Positive Bacilli

Species of Corynebacteria

Corynebacterium
Pathogenic C. diphtheriae
Commensal "Diphtheriods" C. hofmannii, C. xerosis, C. acne
C. diphtheriae is the only pathogenic members of this genus
It caused diphtheria
Normal flora of RT, urethra, vagina, Skin

C. diphtheriae: Causative Agent of Diphtheria

C. diphtheriae pseudomembran.


Corynebacterium diphtheriae can cause pharyngitis which leads to formation of thick grey membrane called pseudo-membrane. The pseudo-membrane is composed of fibrin, dead epithelial cells, bacteria and neutrophils. and then blocks the airway which results in suffocation. As a result of the action of diphtheria toxin into blood stream it acts systemically affecting to peripheral motor neurons and myocardium, life-threatening systemic complications (principally loss of motor function and congestive heart failure) may develop.
Pathogenicity

Pseudomembrane

Corynebacterium diphtheriae
Gram positive Bacilli demonstrat pleomorphism( coccobacillary ), with characteristic morphology (club shaped and beaded) the beads are intracellular store of polymerized phosphate .They divided by ‘snapping fission’and hence are arranged angles to each other ,resembling (chinese characters )Cell wall contain mycolic acid

Non motile Non spore forming Non capsulated aerobic Breakdown glucose by oxidative and fermentative. C. diphtheriae is fastidious while diphtheriods are non-fastidious Catalase positive Oxidase negative


* Species :- C. Diphtheriae (diphtheria). Which contain 3 strains :- C. d. gravis C. d. mitis C. d. intermedius

Non pathogen:

C. hofmannii C. xerosis

Laboratory diagnosis

1 Stain1-Gram stain: C. diphteriae are gram positive bacilli arranged in Chinese letters form often club shaped2-Neisser methylene blue stain: C. diphteriae appears beaded due to the presence of intercellular “Metachromatic " granulesBy stain, the granules appear red while the rest of organism appears blue.-3- Albert stain dark purple by Albert staining method.

Gram stain of C. diphtheriae

Neissermethylene blue stain
metachromatic granules
Albert stain


(Specimen: A throat swab) 2 Culture:. 1- On Loeffler's serum medium: Corynebacteria grow much more easily 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
Loefflers serum

2- On blood tellurite agar.It is selective medium for isolation of C. diphtheriae (Potassium tellurite)3 biotypes of C. diphtheriae are characterized on BTAi.e. Gravis, mitis and intermedius biotypesThe most severe disease is associated with the gravis biotype Colony of gravis biotype → 3mm . Radical form, Raised center.Colonies of mitis biotype are 2.4 mm, small, hemolytic and black Colonies of intemedius biotype are 1-2 mm, intermediate in size, non-hemolytic with black center & grey margin.

C. diphtheriae on BTA

3-Biochemical Reaction

Catalase (+) Oxidase (-) Gelatinase (-) Urease (-) Phosphatase (-)

Table indentification of Corynebacterium strains

H2S
Urease
Starch
Sucrose
Glucose
Catalase
M.O
+ - -
- - -
+ - -
- - -
+ + +
+ + +
C. d. gravis C. d. intermedias C. d. mitis



4-TOXIGENICITY

Detection of exotoxin

I- In vivo
II- In vitro
Two guinea pigs are used
One is used as Test
The second is used as Control
Injected with diphtheria antitoxin
Both test and control injected with isolated MO
If both GP live
If control live & test die
Diphthrioids 0r non-toxigenic C. diphtheriae i.e. non pathogenic
C. diphtheriae i.e. produce exotoxin
If both the test and control show illness or die= It is another organism.


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 Procedure: A strip of filter paper impregnated with diphtheria antitoxin is placed on the surface of serum agar The organism is streaked at angels to the filter paper Incubate the plate at 37C for 24-48 hrs.



Resuls: 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 interaction of the strip and the growth of organism
Filter paper saturated with diphtheria antitoxin
Inoculated M.O.
Positive Elek’s Test Lines of precipitations

* abed elkader elottol

Non pathogen Corynebacteriae Spp.* Diphtheriods :- 

Diphtheroids

Diphtheria
G+ , short and thick Absence Grow on ordinary media Fermentation of glucose , sucrose Usually non toxic positive
A- morphology G+ and thin meta chromatic granules B- culture Grow on enrich media C- biochemical test Fermentation of glucose D- Toxogenicity they are toxic E- Urease test negative

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