1. 2010-2011
2nd 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 Topics
1. Staphylococcal food poisoning 16. Epidemics of meningitis in the
2. Staphylococcus aureus toxic shock syndrome Meningitis Belt in Africa
(TSS) 17. Local and systemic effects of diphtheria
3. Staphylococcus Scaled Skin Syndrome (SSSS) 18. Clinical Diagnosis of Tetanus (effects of
4. Community acquired methicillin resistant tetanospasmin)
S.aureus (CA-MRSA) 19. Physical diagnosis of botulism
5. 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 Protocols
9. Three types of anthracis 24. Types of human viruses and
10. Case-definitions in anthracis Bactriophages
11. Antibiotic sensitivity testing 25. H1N1
12. Supporative streptococcal diseases 26. Outline Classification of fungi (Four
13. Nonsupporative streptococcal diseases classes)
14. Gonorrhea differences in men and women 27. Differences between Prokaryotic and
Eukaryotic cells
15. 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 antibodies
Diphtheria 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- Albert's 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 positives
Check the toxigenicity
 Animal inoculation Guinea pigs/rabbits
 Death within 96 hrs

8. Toxin production test by Elek's plate test (at 37C for 24 hrs}
Precipitin lines
Streak Test Strain on plate
Filter paper with antitoxin antibody
To test production of exotoxin from toxigenic strains of
Corynebacterium diphtheriae to differentiate from normal
flora…..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