Transcript Corynebacterium Corynebacterium  Classification  Corynebacterium diphtheriae and diphtheroids (look like C. diphtheriae) are Gram- positive, club shaped rods.     Some are saprophytic Some produce disease in animals. C.

Corynebacterium
Corynebacterium
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Classification
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Corynebacterium diphtheriae and diphtheroids
(look like C. diphtheriae) are Gram- positive,
club shaped rods.
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Some are saprophytic
Some produce disease in animals.
C. diphtheriae is the most important pathogen in the
group.
Morphology and cultural characteristics
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Small G+B; arrangement=palisade or Chinese
letters
Growth on B.A – raised, translucent, gray colonies
Diphtheroids Gram stain
Arrangement of C. diphtheria
Corynebacterium
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Loeffler‘s agar slant contains serum and
egg that enhance the formation of
metachromatic granules (polymerized
polyphosphoric acid) in C. diphtheriae.
Also called Babes-Ernst granules.
 They are visualized by staining with
methylene blue.
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Methylene blue stain from
Loefflers slant
Corynebacterium
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A medium containing tellurite should be used to
select for Corynebacterium and other
G+ organisms -it inhibits G organisms. Two kinds
are used:
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Cystine tellurite has a longer shelf life
Tinsdale helps to differentiate amongst the
Corynebacterium.
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Colonies on either appear black or gray due to tellurite
reduction.
S. aureus and Listeria also grow as black colonies.
On Tinsdale C. diphtheriae, ulcerans, and
pseudotuberculosis form brown halos around the colonies
due to formation of ferric sulfide.
Corynebacterium
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3 morphological types of C. diphtheriae are found
on tellurite containing media:
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Mitis – black colonies with a gray periphery
Gravis – large, gray colonies
Intermedius – small, dull gray to black.
All produce an immunologically identical toxin.
Incubation -35-370 C for 24 hours.
They prefer a pH of 7.8-8.0 for good growth.
They require access to oxygen (poor AnO2 growth).
Biochemistry
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Catalase +
Corynebacterium
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Nonmotile
C. ulcerans is urease +, C. diphtheriae is -, and C.
pseudotuberculosis is usually +
Virulence factors C. diphtheriae
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For C. diphtherias to cause diphtheria an exotoxin
must be produced.
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Is a heat-labile polypeptide produced during lysogeny of a
 phage that carries the "tox” gene.
Alkaline pH of 7.8- 8.0, aerobic conditions, and a low
environmental iron level are essential for toxin production
(occurs late in the growth of the organism).
The toxin inhibits protein synthesis by ADP-ribosylating
elongation factor 2.
What other organism produces a similar toxin?
Corynebacterium
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Trypsin cleaves the toxin into 2 fragments, A and B, that
are linked together by a disulfide bridge.
Fragment B is required for toxin binding to tissue cells
and fragment A contains the toxic activity.
One molecule of toxin can inhibit 90% of the protein
synthesis in a cell.
Systemic effects include heart failure, paralysis and
adrenal hypofunction leading to an Addison’s like disease.
C. ulcerans and C. pseudotuberculosis sometimes
make a diphtheria-like toxin.
C. diphtheria toxin
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Toxin enters through
receptor mediated
endocytosis
 Acidification of
endocytic vesicle
allows A to
dissociate from B
 A enters cycoplasm
C. diphtheria toxin
Corynebacterium
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To prove that an isolate can cause
diphtheria, one must
demonstrate toxin production.
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This is most often done on an Elek plate:
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The organism is streaked on a plate containing low
iron.
A filter strip containing anti-toxin antibody is placed
perpendicular to the streak of the organism.
Diffusion of the antibody into the medium and
secretion of the toxin into the medium occur.
At the zone of equivalence, a precipitate will form.
Elek plate
Corynebacterium
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Guinea pig or tissue culture toxicity assays may
also be done.
Capsule – is protein in nature
 Cord factor – is a complex glycolipid
(trehalose 6,6’-dicorynemycolate) that has
been shown to disrupt mouse mitochondria.
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It has not been shown to play a role in the
production of diphtheria.
Corynebacterium
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Clinical Significance (C. diphtheria)
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Is normally found in the throats of healthy carriers.
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The organism infects only man and it has a limited
capacity to invade.
Diphtheria - Disease usually starts as a local
infection of the mucous membranes causing a
membranous pharyngitis
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Local toxin effects result in degeneration of epithelial
cells.
Inflammation, edema, and production of a
pseudomembrane composed of fibrin clots,
leukocytes, and dead epithelial cells and microorganisms
occurs in the throat.
Diphtheria - pseudomembrane
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This may obstruct the airway and result in
suffocation.
Corynebacterium
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The more dangerous effects occur when the toxin
becomes systemic and attacks the heart
(heart failure), peripheral nerves (paralysis), and
the adrenal glands (hypofunction).
Cutaneous diphtheria More common in tropical
and subtropical areas.
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Necrotic lesions with occasional formation of a local
pseudomembrane occur.
Antibiotic susceptibility and treatment
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Antiserum once the toxin has bound, however, the
antiserum against it is ineffective.
Penicillin to eliminate the organism.
Corynebacterium
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Prevention- Active immunization with toxoid (alum
precipitate).
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Shick skin test like the Dick test in that it tests for
circulating antibody to the toxin by injecting a
small amount of toxin intradermally and observing
for a local erythematous and necrotic reaction.
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Is part of the DPT vaccine.
If this occurs it indicates that the person has no antitoxin antibodies and is, therefore, susceptible to
diphtheria.
Other Corynebacterium are part of the normal
flora of the skin and URT.
Corynebacterium
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Are called diphtheroids and may occasionally
cause disease, particularly in immunocompromised
individuals.
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C. ulcerans toxigenic strains may produce a disease
similar to, but less severe than diphtheria.
J-K Group commonly cause infections in those with
underlying disease.
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Diseases include bacteremia, meningitis, peritonitis, wound
infections, etc.
It is becoming more and more of a problem.
C. pseudotuberculosis found in those with exposure to
animals.
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Can cause pneumonia or lymphadenitis.
Produces a different exotoxin than C. diphtheriae.