Download Gram positive rods bacteria

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Systematic Bacteriology
Lec.(5)
Gram positive rods bacteria
Coryneform bacteria:In the medical laboratory coryneform bacteria defined as pleomorphic
gram positive rod which stain irregularly are arranged in V form, non-motile
catalase positive and non- acid fast forming acid but not gas from CHO
Genus: Corynebactrium:
Is the causative organism of diphtheria, a localized inflammation of the
throat with grayish white adherent exudates (pseudo membrane) and a
generalized toxemia due to the secretion and dissemination of a highly
potent toxin?
This genus consists of species that are gram positive straight or curved rod
contains volutin granules (intracytoplasmic polyphosphate bodies) when
stained with Neisser or Albert stain it stained dark purple color.
They are non-motile, non-sporing and non- capsulated and may stained
irregularly (can be easily decolorized) and so beaded or barred resembling
Chinese lettering
Habitat:
These organisms are normally found in soil, plant and animal. Non
pathogenic strain form part of flora of the skin, upper respiratory tract,
urinary tract and conjunctiva.
DR. YAGOUB HAMADT Allah
1
albah university
Page 2 of 5
Systematic Bacteriology
Lec.(5)
Medical important species:
*
C diphtheriae (contain three biovar) C.gravis, C.intermedius, and
C.mitis (some time this classification according to severity)
*
C. ulcerance
C.haemolyticum
C.pyogenes
C ovis (pseudo tuberculosis)
* Commensals are C, hofmanii and C.xerosis
Pathogenecity:
C diphtheriae cause nasal, nasopharyngeal and tonsilar diphtheria mostly
among young children.
Transmission by inhalation of infected droplets or by contact with
contaminated object (Nasal carriers are particularly dangerous because they
shed large numbers of bacilli.
 virulence strain produce specific exotoxin which are absorbed into
mucus membrane destroying epithelium and resulting in the fibrinous
exudates
containing
bacteria,
leucocytes,
erythrocytes,
and
disintegrating epithelial cells. All these combine to form a grey
pseudo membrane that is characteristic of diphtheria infection.
 Diphtheria is a toxaemic infection the organism is usually remains at
the site infection.
 Diphtheria toxin is heat-stable polypeptide which is composed of two
fragments (A&B). Fragment B is required for transport of fragment A
into the cell, where it inhibits polypeptide chain elongation at the
DR. YAGOUB HAMADT Allah
2
albah university
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Systematic Bacteriology
Lec.(5)
ribosome. Inhibition of protein synthesis is probably responsible for
both the necrotic and neurotoxic effects of the toxin.
 The pseudo membrane can mechanically obstruct the passage of air in
the larynx and cause death
 Acute circulatory failures which may be peripheral or cardiac, septic
condition such as pneumonia and otitis media may results as a
complication of infection.
 Cutaneous (skin) diphtheria is as a result of infection of open wounds,
this infection is generally milder than respiratory infection
Diagnosis:
Important:
because of powerful and rapidly fatal exotoxin
produce by C diphtheriae a patient suspected of having diphtheria is
treated immediately with antitoxin.
Specimens:
Include throat and or nasopharyngeal swab and skin swab if cutaneous
diphtheria is suspected
Staining and morphology:
C diphtheriae is gram positive but usually stains weakly. Its markedly
pleomorphic long, thin and curved forms can be seen. They often appear in
clusters, joined at angles like Chinese letters.
DR. YAGOUB HAMADT Allah
3
albah university
Page 4 of 5
Systematic Bacteriology
Lec.(5)
Volutin granules:
In Albert stained smear C diphtheriae often appears beaded due to presence
of dark – staining granules in the rods. Volutin granules are energy storing
inorganic phosphate units.
C diphtheriae is non- motile, non- capsulated and non- sporing.
Culture:
C diphtheriae is aerobic and facultative anaerobic grow better at 37 C
Loffler serum medium and Dorset egg medium grow rapidly on these media
producing significant growth in 4-6 hours.
Tellurite blood agar selective media for isolation of C diphtheriae from
throat and nasopharyngeal swab it produce grey – black colonies (its non hemolytic)
Biochemical Test:
 Catalase test positive
 Oxidase test negative
 Urease test negative
 Ferments glucose and maltose with acid production but without ga
Toxigencity:
 Elek gel precipitation test (in vitro test)
 Animal inoculation ( in vivo test)
 Schick test
DR. YAGOUB HAMADT Allah
4
albah university
Page 5 of 5
Systematic Bacteriology
Lec.(5)
Antimicrobial sensitivity

Antitoxin is used to neutralized C diphtheriae toxin

Antibiotic with activity against C diphtheriae include penicillin,
erythromycin, clindamycin and vancomycin.
Differentiation test for Corynebacterium species:
Species
glucose maltose srarch sucrose urease nitrate hemolytic
C.gravis
+
+
+
+
+
C.intermedius
+
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C.mitis
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+
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+
C.ulcerance
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+
+
+
+
C.ovis
+
+
+
D
+
C.xerosis
+
+
+
C.hofmanii
+
+
JK group
+
D
C.hemolyticum
+
+
+
+
+
DR. YAGOUB HAMADT Allah
5
albah university