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2nd term lectures,_cd,_listeria,diphoids[1]

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  • 1. 2010-20112nd Term 2nd Semester
  • 2. Gram positive non-sporing bacilli: Corynebacterium diphtheriae, dipherioids, and Listeria monocytogenes 1. Corynebacterium diphtheriae (Klebs-Löffler bacillus) Points to consider: Dephtheria is a very old historical disease was called the strangling angel of children‘ in the 4th century BC. The then father of medicine, Hippocrates, was the first to describe it. Respiratory diphtheria (pseudomembrane on pharynx) and cutaneous diphtheria Prototype A-B exotoxin acts systemically Toxoid in DPT and TD vaccines Diphtheria toxin encoded by tox gene introduced by lysogenic bacteriophage (prophage) Selective media: cysteine-tellurite; serum tellurite; Loeffler’s Three speceis are known:  C. diphtheriae mitis, C. diphtheriae intermedius, C. diphtheriae gravis, and  Gravis, intermedius, and mitis colonial morphology
  • 3. Seminar Topics1. Staphylococcal food poisoning 16. Epidemics of meningitis in the2. Staphylococcus aureus toxic shock syndrome Meningitis Belt in Africa (TSS) 17. Local and systemic effects of diphtheria3. Staphylococcus Scaled Skin Syndrome (SSSS) 18. Clinical Diagnosis of Tetanus (effects of4. Community acquired methicillin resistant tetanospasmin) S.aureus (CA-MRSA) 19. Physical diagnosis of botulism5. Basic principles in Strain Typing (DNA foodpoisoning Fingerprinting) 20. Reasons for Clostridium difficile-6. Polymerase Chain Reaction (PCR) principles Associated Diarrhea (CDAD)7. DNA sequencing principles 21. How vaccines work?8. Streptococcal necrotizing fasciitis (flesh 22. Listeriosis: causes, reasons, risk groups eating disease) 23. Laboratory Safety Protocols9. Three types of anthracis 24. Types of human viruses and10. Case-definitions in anthracis Bactriophages11. Antibiotic sensitivity testing 25. H1N112. Supporative streptococcal diseases 26. Outline Classification of fungi (Four13. Nonsupporative streptococcal diseases classes)14. Gonorrhea differences in men and women 27. Differences between Prokaryotic and Eukaryotic cells15. Waterhouse-Friderichsen Syndrome 28. Antimicrobial resistance 29. Nsoscomial Multidrug resistance 30. DNA
  • 4. Two types of diphtheria syndromes: 1. Local toxigenic effects: elicit inflammatory response and necrosis of the faucial mucosa cells-- formation of "pseudo- membrane“ (composed of bacteria, lymphocytes, plasma cells, fibrin, and dead cells), causing respiratory obstruction. 2. Systemic toxigenic effects: necrosis in heart muscle, liver, kidneys and adrenals. Also produces neural damage. http://www.vaccineinformation.org/photos/i ndex.asp
  • 5. CORYNEBACTERIA  Prevalent in baby’s after 3-6 months (that’s why DPT is given at 2, 4, 6 months, boosters at 18 months and at school entry), very high in young children  Shick test – identiies non immune people: diluted stabilized toxin I/Derm, localized erythema (1-3cm) in 2-4 days, means no or little antibodiesDiphtheria Skin lesion on leg
  • 6. Morphology Aerobic Gram +ve bacilli, nonmotile, uncapsulated, club-shaped rod In stained smears bacilli are palisade Chinese letter arrangement Metachromatic granules at poles) give the rod a beaded appearance. Corynebacterium diphtheriae  Normal flora of nasopharynx  Diphtheria caused when infected by lysogenic Bacteriophage (heat labile toxin A and B) Diptheroids  Normal flora of skin  Can cause disease in ‘compromised’ host C. diphtheriae has Three biotypes  Gravis (severe)  Inter-medius (intermediate)  Mitis (mild) Portal of entry: respiratory tract or skin abrasions.
  • 7. Some Lab Diagnostic properties Direct smear -Gram stain- Gram positive bacilli:  Straight/curved , enlarged(club-shaped) at ends  Arranged Chinese letters or V shape Direct smear- Alberts stain, special strain for metachromatic granules  Loeffler’s egg-serum agar slope for metachromatic granules, (also called polyphosphates, volutine granules, or Babes-Ernst granules) Catalase positive Selective media  Cystine-potassium-tellulrite medium, black colonies, inhibits diphtherioids and other Gram positivesCheck the toxigenicity Animal inoculation Guinea pigs/rabbits  Death within 96 hrs
  • 8. Toxin production test by Eleks plate test (at 37C for 24 hrs} Precipitin linesStreak Test Strain on plate Filter paper with antitoxin antibodyTo test production of exotoxin from toxigenic strains ofCorynebacterium diphtheriae to differentiate from normalflora…..diphtheriods
  • 9. Brief Outline on Diphtheria Management 1. Patients–isolate patients/bed rest/antibiotic treatment/antitoxins (horse serum) Penicillin/erythromycin/teracycline/rifampicin/clindamycin 2. Contacts – immunize if not (toxoid) – adults should be schick tested or given low dose as immunization of immune adults can result in severe reaction.  prophylactic antibiotic – erythromycin  swab nose and throats of contacts 3.Community – immunization Prevention: Active immunization with toxoid (DTPa-hib) Other corynebacteria are normal flora of the skin and URT  Called diphtherioids, cause disease only in compromised patients
  • 10. Basic principles of immunizaiton When small amount of diluted diphtheria toxin (0.1 ml) is injected in the skin, a skin reaction occurs ( a ring of 5–10 mm diameter) if a person is not immunized…If a person is immunized antibodies will neutralize the toxin and no rxn
  • 11. Listeria monocytogenes The only strain the infects humans Fridge-Friendly Pathogen Gram positive, motile tumpling, beta hemolytic, uncapsulated nonsporing, coccobacilli http://www.youtube.com/watch?v=fjD_ruKmSfA Tumbling Resistant to cold, heat, salt, pH extremes and bile Grow in refrigeration (Food poisoning risk) Most common foodborne outbreaks Usually food-borne transmission, asymptomatic intestinal carrier High risk:  Neonates  Elderly and  pregnant women Listeriosis - most cases associated with dairy products, poultry, and meat Virulence attributed to ability to replicate in the cytoplasm of cells after inducing phagocytosis; avoids humoral immune system Invasive and Intracellular
  • 12. Clinical signs of Listeriosis Bacteremia and sepsis CNS listeriosis (meningitis, meningoencephalitis, cerebritis, brainstem encephalitis, and brain or spinal abscess) Endocarditis Focal infections Recurrent spontaneous abortion granulomatosis infantisepticum Diagnostic Aids:  CAMP test positive (strep)  Culture requires lengthy cold enrichment process.  Rapid diagnostic tests using ELISA available
  • 13. Treatment and Control For severe infections:  Ampicillin (200 mg/kg/d i.v. divided in six doses) or Penicillin (300,000 mg/kg/d i.v. divided in six doses)  Combined with gentamicin (1–2 mg/kg every 8 hours, adjusted with renal function and followed by levels) Penicillin-allergic patients:  Trimethoprim-sulfamethoxazole (20 mg/kg per day of the Trimethoprim component IV in four divided doses) Combination of ampicillin and trimethoprim- sulfamethoxazole might be more effective