NAJRAN UNIVERSITY College of Applied Medical Sciences

1. NAJRAN UNIVERSITY College of Applied Medical Sciences Clinical Bacteriology 1 By Dr. Ahmed Morad Asaad Associate Professor of Microbiology

2. 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

3. 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

7. 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

10. 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

11. 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

13. 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

14. 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

15. 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

16. 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