This document discusses Gram positive bacilli including Corynebacterium and Listeria. It focuses on Corynebacterium diphtheriae, providing details on its morphology, culture characteristics, virulence factors causing diphtheria, clinical manifestations of disease, diagnosis and prevention through vaccination. It also briefly discusses Listeria monocytogenes and its ability to cause neonatal meningitis through contaminated food consumption by the mother.

1. Gram positive bacilli
Non-spore forming
- Corynebacterium
- Listeria
Spore- forming
- Bacillus
- Clostridium

2. Non-spore forming
Corynebacterium

3. Corynebacterium
 Some species are part of normal flora of
skin and mm.
 Medically important species is
Corynebacterium diphtheriae

4. Morphology
 Gram-positive bacilli
 Club-shaped
 Arranged at acute angles or
parallel to each other
(Chinese letters).
 Meta-chromatic granules.
 Non-spore forming

6. Methylene blue stain:
Beaded appearance

7. Culture Characters
 Aerobic.
 Growth on:
1. Blood agar
2. Loeffler’s serum:
Best morphology
3. Blood tellurite agar:
Selective & differential
Grey to black colonies

8. Virulence factors
Diphtheria ExotoxinDiphtheria Exotoxin
Exotoxin is dependent on:
1. Lysogenic prophage.
2. Low extracellular iron
concentration.

9. Disease: Diphtheria
 Upper respiratory tract infection.
 Transmitted by droplets.
 Characterized by:
1- Local pseudomembrane.
2- Toxemia.
 Complications:
 Airway obstruction
 Toxic myocarditis and heart failure
 Nerve paralysis

10. Clinical Manifestations
- Cervical lymphadenitis
(Bull neck)
- Toxaemia with low grade fever
D.D. of sore throat:
1- S. pyogenes
2- Vincent’s angina
3- C. diphtheriae

11. Diagnosis
Mainly clinical
Laboratory confirmation:
A- Specimen:
Throat swab from the
pseudomembrane.

12. B- Direct Detection:
Microscopic examination (Gram stain):
• Gram-positive bacilli
• Chinese letters appearance

13. B- Direct Detection:
Microscopic examination (Methylene Blue stain):
Meta-chromatic granules

14. 1- Loeffler’s serum:
Best morphology
2- Blood tellurite agar:
grey/black colonies
3- Blood agar to
exclude S. pyogenes
C- Cultivation:

15. D- Identification:
Microscopic examination:
1- Gram stained smear:
Gram-positive club-shaped
bacilli (Chinese letters).
2- MB stained smear: showing
meta-chromatic granules.

16. The isolated organism is
Corynebacterium diphtheriae
Is it Toxigenic or Not?

17. E- Toxigenicity Tests:
a) Elek’s test: most common assay.
b) PCR: detection of toxin gene.
c) ELISA: detection of toxin from culture.

18. Elek’s test:
An antigen-antibody reaction in which the
Ag is soluble “Precipitation”.

19. Elek’s Test

20. Diagnosis of carriers
Throat or nasal swabs are subjected to
the same procedures:
Isolation
+
Toxigenicity tests

21. What treatment is prescribed?
 Treatment should be IMMEDIATELY started
if diphtheria is clinically suspected.
 Diphtheria antitoxin and antibiotics.
 Treatment of symptoms & complications
e.g. respiratory support.

22. How can we prevent this disease?
By Vaccination
Diphtheria toxoid + pertussis vaccine +
tetanus toxoid in a trivalent vaccine:
DPT
For close contacts of a case:
(booster of diphtheria toxoid + antibiotic
chemoprophylaxis)

23. Diphtheroids
Corynebacteria that resemble C.diphtheriae in
morphology.
They are mainly commensals.

24. Case
 A 4-year-old male child
presented with fever of 38°C.
 Physical examination
revealed clear chest,
exudative pharyngitis and
bilaterally enlarged cervical
lymph nodes.
 A throat culture was taken
and a course of penicillin was
started.

25. Case (cont.)
 The child’s course worsened, he
became increasingly lethargic,
developed respiratory distress and
was hospitalized.
 On admission, he had a fever of
38°C and an exudate in the
posterior pharynx described as a
yellowish, thick membrane which
bled when scraped and removed.
 The patient’s medical history
revealed that he had received no
immunizations.

26. Listeria

27. Listeria monocytogenes
Gram-positive
rods
(coccobacilli)
Microscopic examination:

28. Listeria resembles Corynebacteria in
morphology but is MOTILE.

29. Diseases
 Abortion, premature delivery or sepsis
during the peripartum period.
 Neonatal meningitis
 Septicaemia and meningitis (in
immunocompromised adults).
 Food poisoning (dairy products or
undercooked meat)

30. Neonatal meningitis
 Meningitis caused by Listeria is almost
always seen in neonates.
 Causes of Neonatal Meningitis:
1. Group B Streptococci
2. E. coli K1
3. Listeria monocytogenes

31. Case
A one month old girl was admitted to hospital
with acute meningitis.
The Gram stain of CSF revealed Gram-positive
short rods.
What is the cause of neonatal meningitis?
a. N. meningitidis, group A
b. N. meningitidis, group C
c. Listeria monocytogenes
d. S. pneumoniae

32. How did the mother contract it?
 Listeriosis is a food-borne infection.
 Listeria resists drying, heating and freezing
without forming spores.
 Commonly contaminated food items:
1. Dairy products (esp. unpasteurized milk and
soft cheeses).
2. Undercooked meat (chicken, hot-dogs).
3. Refrigerated food.

33. Review Questions

34. 1- C.diphtheriae is cultured on:
a- Nutrient agar.
b- Chocolate agar.
c- Loffler’s serum.
d- Lowenstein-Jensen medium.
e- MacConkey’s agar.

35. 2- Blood tellurite agar is a(n):
a- Enriched medium
b- Enrichment medium
c- Simple medium
d- Selective and differential medium
e- Indicator medium only

36. 3- Which of the following is a toxigenicity test
for C.diphtheriae ?
a- Elek’s test
b- Coagulase
c- Catalase test
d- Culture on blood tellurite
e- ELISA test for antibody detection

37. 4- C. diphtheriae has the following morphology:
a- Gram negative cocci arranged in pairs
b- Gram positive cocci arranged in chains
c- Gram positive club-shaped bacilli
d- Gram positive cocci in clusters
e- Gram positive capsulated diplococci

38. 5- The toxin of C. diphtheriae is only produced
by those strains that are:
a- Encapsulated.
b- Glucose fermenters.
c- Sucrose fermenters.
d- Lysogenic
e- Endotoxin producers.

39. 6- A 1-week old newborn develops meningitis.
Short gram-positive rods are isolated. The
mother had eaten unpasteurized cheese during
pregnancy. What is the most likely etiological
diagnosis?
a- C. diphtheriae.
b- S. pyogenes.
c- L. monocytogenes.
d- S. pneumoniae.
e- S. agalactiae

40. THANK YOU