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NAJRAN UNIVERSITY College of Applied Medical Sciences. Clinical Bacteriology 1. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. The genus Corynebacteria It includes: C. diphtheriae : Exotxin producer – causing diphtheria in man

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Najran university college of applied medical sciences

NAJRAN UNIVERSITY

College of Applied Medical Sciences

Clinical Bacteriology 1

By

Dr. Ahmed Morad Asaad

Associate Professor of Microbiology


Najran university college of applied medical sciences

The genus Corynebacteria

It includes:

C. diphtheriae:Exotxin producer – causing diphtheria in man

Propionobacterium: Anaerobic – members of normal flora of skin & mucous membrane – involved in acne

Commensal species (diphtheroids): flora in mucous membrane of R.T and GIT – may cause diseases in immunocompromisedpersones – C. ulcerans (diphtheria-like illness)

Listeriamonocytogenes: mainly in animals – may cause sever diseases in man

Actinomyces: anaerobic – causing actinomycosis


Najran university college of applied medical sciences

C. Diphtheriae (Diphtheria bacillus)

A powerful exotoxin producer (Viruelence factor)

Causative organism of Diphtheria

Characters:

1- Gram +ve bacilli (often club-shaped) – Chinese letter appearance

2- Contain intracellular metachromatic granules (Volutin granules)

3- Non-capsulated – non-motile

4- Catalase +ve – Oxidase +ve – Facultative anaerobe – Grow better under aerobic conditions


Najran university college of applied medical sciences

Culture Characters:

1- Grow on Loffler’s serum

2- On blood agar: Colonies are small, grey, small areas of complete haemolysis

2- On blood tellurite agar: colonies are grey to black – 3 biotypes can be recognized on the basis of colony morphology and severity of disease


Najran university college of applied medical sciences

Diphtheria

Human is the natural host. Both toxigenic and non-toxigenic organisms are in URT and transmitted by droplet infection. Conjunctival and skin diphtheria ocuur in tropics and spread by contact.

Pathogenesis:

1- Cases or carriers are harboring the organism in URT

2- Infection by droplet infection

3- 1ry lesion is in throat or nasopharynx by formation of pseudomembrane

4- The microbe multiply – produce toxin – into blood stream – distant organs


Najran university college of applied medical sciences

6- Toxin production is a lysogenic property

7- All strains produce an identical toxin (Only one antigenic type of the toxin

5- Paralysis of soft palate – eye muscles – extremities – Its action is irreversible


Najran university college of applied medical sciences

  • Lab Diagnosis:

  • To confirm clinical diagnosis

  • Specific treatment with antitoxin should NEVER wait for lab results

  • Diagnosis of the case

  • Specimen: Swab from the membrane

  • Direct smear stained with:

  • Gram’s stain: to show the organism morphology

  • Methylene blue: To show beaded appearance


Najran university college of applied medical sciences

  • Diagnosis of the carrier

  • To isolate the organism in pure form and test its ability to produce toxin

  • Isolation of the organism

  • Specimen: Swab from the membrane

  • Direct smear stained with:

  • Gram’s stain: to show the organism morphology

  • Methylene blue: To show beaded appearance

  • Culture on selective media


Najran university college of applied medical sciences

  • Virulence tests (Tests for toxigenicity)

  • In vivo tests:

  • The culture suspension is injected into 2 guinea pigs – one of them received 250 units of diphtheria antitoxin 2 hours before the test.

  • If the protected animal survives and the unprotected dies within 2 -3 days = The strain is toxigenic

  • If the 2 animals survive = The strain is non-toxigenic


Najran university college of applied medical sciences

  • In vitro test (Elek’s test):

  • The isolated organism is streaked across a serum agar plate

  • A filter paper strip impregnated with antitoxin is placed on the surface of the medium at right angle to the organism

  • After 48 h, the plate is inspected for lines of precipitation

  • Presence of these lines = The strain is toxigenic

  • Tissue culture test (Agar overlay):

  • The strain is streaked into an agar overlay of a tissue culture

  • If the strain is toxigenic, the toxin will diffuse into the tissue and kill the cells


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