Page 1 of 5 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 organismsare normally found in soil, plant and animal. Non pathogenic strain form part of flora of the skin, upper respiratory tract, urinary tract and conjunctiva.

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 diphtheriaecause 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 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 diphtheriaeis 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.

Volutin granules:

In Albert stained smear C diphtheriaeoften 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 diphtheriaeis 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 diphtheriaefrom 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

Antimicrobial sensitivity

  • Antitoxin is used to neutralized C diphtheriaetoxin
  • Antibiotic with activity against C diphtheriaeincludepenicillin, erythromycin, clindamycin and vancomycin.

Differentiation test for Corynebacterium species:

Species / glucose / maltose / srarch / sucrose / urease / nitrate / hemolytic
C.gravis / + / + / + / - / - / + / +
C.intermedius / + / + / - / - / - / + / -
C.mitis / + / + / - / - / - / + / +
C.ulcerance / + / + / + / - / + / - / +
C.ovis / + / + / - / - / + / D / +
C.xerosis / + / + / - / - / - / + / -
C.hofmanii / - / - / - / - / + / + / -
JK group / + / D / - / - / - / - / -
C.hemolyticum / + / + / + / + / - / - / +

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DR. YAGOUB HAMADT Allah albah university