Diphtheria is a highly infectious disease caused by the bacterium Corynebacterium diphtheriae, characterized by throat infections and toxin production leading to severe complications. The bacterium exhibits unique morphological features such as club-shaped bacilli and metachromatic granules, and its diagnosis involves specific laboratory tests. Vaccination with diphtheria toxoid is crucial for prevention, and treatment includes antitoxin administration and antibiotics but must be initiated promptly upon suspicion of the disease.

1. BACTERIAL
PHARYNGITIS

2. DIPHTHERIA
2

3. INTRODUCTION
 Diphtheria - highly infectious childhood disease caused by -
Corynebacterium diphtheria.
 Primarily infects - throat and produces toxin (diphtheria toxin) -
causes an exudative pharyngitis and membranous tonsillitis.
3

4. INTRODUCTION (CONT..)
 Genus Corynebacterium - gram-
positive, noncapsulated, non-
sporing, non-motile bacillus.
 Irregularly stained - shows club-
shaped swellings.
4
A B
Club-shaped bacilli in methylene
blue-stained smear

5. INTRODUCTION (CONT..)
 1. Chinese letter or cuneiform
arrangement: Appear as V- or L-shaped
in smear - bacterial cells divide and
daughter cells tend to lie at acute
angles to each other - snapping type of
division .
 2. Metachromatic granules: Present at
ends or poles of the bacilli.
5
A B C
Gram-stained smear shows
V- or L-shaped bacilli with
cuneiform arrangement

6. METACHROMATIC GRANULES
 Also called polar bodies or Babes–Ernst bodies or volutin
granules).
 Storage granules of the organism, composed of
polymetaphosphates
 Granules - stained strongly gram-positive compared to
remaining part of the bacilli.
 Granules take up bluish purple metachromatic color - stained
with Loeffler’s methylene blue 6

7. METACHROMATIC GRANULES (CONT..)
 Better stained with special stains - Albert’s,
Neisser’s and Ponder’s stain.
 Granules - well developed on enriched
media - blood agar or Loeffler’s serum
slope
 Volutin granules - also possessed by -
Corynebacterium xerosis and Gardnerella
vaginalis.
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A B C

8. HISTORY
 Ancient disease, known since the time of Hippocrates.
 First recognized by Pierre Bretonneau (1826) - (Greek word
diphtheros— meaning leather like) - leathery
pseudomembrane formation over the tonsil
 First observed by Klebs (1883)
 First cultivated by Loeffler (1884) - Klebs-Loeffler bacillus.
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9. VIRULENCE FACTORS (DIPHTHERIA
TOXIN)
 Toxin -polypeptide chain, comprises of two fragments—A
(active) and B (binding)
 Fragment B binds to the host cell receptors - helps in entry of
fragment A
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10. MECHANISM OF DIPHTHERIA TOXIN (DT )
 Fragment A -active fragment - causes ADP ribosylation of
elongation factor 2 (EF-2) → leads to inhibition of EF-2 → leads
to inhibition of translation step of protein synthesis.
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11. FACTORS REGULATING TOXIN
PRODUCTION
 Phage coded: β-corynephage - carrying tox gene.
 Iron concentration: 0.1 mg per liter
 Other species: Also produced by C. ulcerans and C.
pseudotuberculosis.
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12. TOXOID IS USED FOR VACCINATION
 Antigenic and antitoxins are protective in nature. However, as
 It is virulent - cannot be given directly for vaccination.
 Toxin - converted to toxoid - used for vaccination.
 Toxoid - form of toxin – virulence is lost, retaining its antigenicity
12

13. TOXOID IS USED FOR VACCINATION
(CONT..)
 Toxoid formation - promoted by formalin, acidic pH and
prolonged storage
 Park William 8 strain - preparation of vaccine
 LF unit - Limit of flocculation (Lf) unit.
13

14. PATHOGENICITY AND CLINICAL
MANIFESTATIONS
 Diphtheria is toxemia but never a bacteremia
 Bacilli are noninvasive - secrete the toxin - spreads via
bloodstream to various organs
 Toxin responsible for all types of manifestations - local
(respiratory) and systemic complications
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15. RESPIRATORY DIPHTHERIA
 Most common form of diphtheria.
 Tonsil and pharynx (faucial diphtheria) - most common sites
followed by nose and larynx.
 Incubation period - 3–4 days.
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16. RESPIRATORY DIPHTHERIA (CONT..)
 Faucial diphtheria: Diphtheria
toxin elicits an inflammatory
response - leads to necrosis of the
epithelium and exudate formation
and mucosal ulcers - lined by
tough leathery greyish white
pseudomembrane coat.
16
A B
Pseudomembrane covering the tonsils
classically seen in diphtheria

17. RESPIRATORY DIPHTHERIA (CONT..)
 Extension of pseudomembrane -
into the larynx and bronchial
airways - asphyxia.
 Bull-neck appearance - Tonsillar
swelling and neck edema - foul
breath, thick speech, and stridor
(noisy breathing)
17
A B
Bull neck appearance

18. CUTANEOUS DIPHTHERIA
 Punched-out ulcerative lesions with necrosis, due to the
organism itself and is not toxin-mediated.
 Also - caused by nontoxigenic strains.
 Increasing incidence, especially in vaccinated children.
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19. SYSTEMIC COMPLICATIONS
 Neurologic manifestations -Toxin mediated non-inflammatory
demyelinating disorder presented with:
 Cranial nerve involvement & Peripheral neuropathy
 Ciliary paralysis
 Myocarditis
 Typically associated with arrhythmias and dilated
cardiomyopathy.
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20. LABORATORY DIAGNOSIS OF DIPHTHERIA
 Specimen: Throat swab and a portion of pseudomembrane
 Direct smear
 Gram stain: Club shaped gram-positive bacilli with Chinese
letter arrangement
 Albert’s stain: Green bacilli with bluish black
metachromatic granules
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21. LABORATORY DIAGNOSIS OF DIPHTHERIA
(CONT..)
 Culture media
 Enriched medium: Blood
agar, chocolate agar and
Loeffler’s serum slope
 Selective medium: Potassium
tellurite agar and Tinsdale
medium, produces black
colonies
21
A B
A. Loeffler’s serum slope;
B. Potassium tellurite agar shows black
colonies.

22. LABORATORY DIAGNOSIS OF DIPHTHERIA
(CONT..)
 Identification
 Biochemical tests such as sugar fermentation tests using
Hiss’s serum sugar media
 Automated identification systems such as MALDI-TOF or
VITEK
22

23. LABORATORY DIAGNOSIS OF DIPHTHERIA
(CONT..)
Diphtheria toxin demonstration
 In vivo tests (Guinea pig inoculation): Subcutaneous and
intracutaneous tests
 In vitro tests:
 Elek’s gel precipitation test
 Detection of tox gene-by PCR
 Detection of toxin-by ELISA or ICT
 Cytotoxicity on cell lines.
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24. LABORATORY DIAGNOSIS OF DIPHTHERIA
(CONT..)
Diphtheria toxin demonstration
 In vivo tests (Guinea pig inoculation): Subcutaneous and
intracutaneous tests
 In vitro tests:
 Elek’s gel precipitation test
 Detection of tox gene-by PCR
 Detection of toxin-by ELISA or ICT
 Cytotoxicity on cell lines.
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25. ELEK’S GEL PRECIPITATION TEST
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26. ELEK’S GEL PRECIPITATION TEST
(CONT..)
 Isolates 1 to 4 are toxigenic strains
 Isolates 1 and 2: Precipitation bands crossed over – toxins are
not-identical - strains are unrelated
 Isolate 2 and 3: Partial fusion of precipitation bands - strains
are partially related to each other
 Isolates 3 and 4: Precipitation bands fused with each other -
strains are completely related
 Isolate 5 : non-toxigenic strain (no precipitation band is
formed).
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27. TYPING OF C. DIPHTHERIAE
 Useful for epidemiological studies, to know the relatedness
between the isolates.
 Biotyping - use in the past - four biotypes —gravis, intermedius,
mitis and belfanti.
 Vary in virulence and toxin production -gravis100% toxigenic
and more virulent.
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28. EPIDEMIOLOGY
 Incidence decreasing – widespread vaccination coverage
 Source of infection - Carriers (95%) & cases (5%)
 Carriers (0.1% to 5%)
 Temporary (persist for a month) or chronic (persist for a
year).
 Nasal carriers (more dangerous - frequent shedding) &
throat carriers
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29. EPIDEMIOLOGY (CONT..)
 Transmission - respiratory droplets or rarely by contact with
infected skin
 Reservoir - Humans are the only reservoir
 Age - Common age affected - 1–5 years.
 Shift from preschool to school age with immunization
 Newborns - maternal antibodies protective
 Global situation - Due to wide spread immunization, cases
were drastically declined by >95% over last 3 decades.
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30. EPIDEMIOLOGY (CONT..)
 Resurgence of diphtheria
 In 2019, outbreaks – Tamil Nadu, Kerala and Karnataka and
few other states
 Majority (>70%) of cases - children 5–10 years or more - low
coverage of diphtheria vaccine especially the booster doses -
primary cause of its resurgence
 Waning immunity in adults - minor cause contributes to adult
diphtheria.
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31. TREATMENT OF DIPHTHERIA
 Treatment - started immediately on clinical suspicion of
diphtheria.
 Antidiphtheritic serum or ADS (antitoxin): Passive immunization
- antidiphtheritic horse serum - neutralizes the toxin.
 A test dose should be given to check for hypersensitivity
 It is given either IM or IV and the dose depends on stage of
illness:
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32. TREATMENT OF DIPHTHERIA (CONT..)
 Early stage (< 48 hours): 20,000–40,000 units
 If pharyngeal membranes present: 40,000–60,000 units
 Late stage (> 3 days, with bull neck): 80,000–120,000
units.
 Human antitoxin therapy is under development.
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33. TREATMENT OF DIPHTHERIA (CONT..)
 Antibiotics: Penicillin or erythromycin is the drug of choice.
 If given early (<6 h of infection), before the toxin release
 Prevent further release of toxin by killing the bacilli
 Treatment of cutaneous diphtheria
 Treatment of carriers: Drug of choice is erythromycin.
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34. PROPHYLAXIS - POST-EXPOSURE
PROPHYLAXIS
 For close contacts (e.g. household), booster dose of
diphtheria vaccine + penicillin G (single dose) or erythromycin
(7–10 days) is recommended.
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35. PROPHYLAXIS - VACCINATION
 Protective titer >0.01 Unit/mL of antitoxin
 Vaccine not effective for - cutaneous diph. & carrier state
 Types of Vaccine:
 Single vaccine: Diphtheria toxoid (alum or formal
precipitated)
 Combined vaccine:
35

36. PROPHYLAXIS – VACCINATION (CONT..)
 Combined vaccine:
 DPT: Contains DT (diphtheria toxoid), Pertussis (whole cell) &
TT
 DaPT: Contains DT, TT and acellular pertussis (aP)
 Td: Contains tetanus toxoid and adult dose (2 Lf ) of
diphtheria toxoid
 Pentavalent vaccine: DPT + hepatitis B and Haemophilus
influenzae
type b.
36

37. PROPHYLAXIS – VACCINATION (CONT..)
 Administration of Diphtheria Vaccine:
 Schedule: Under National Immunization Schedule (NIS) of
India 2020 (Chapter 20, Table 20.4):
 Children: Total seven doses are given.
 Three doses at 6, 10 and 14 weeks of birth
 Booster doses at 16–24 months & 5 years
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38. PROPHYLAXIS – VACCINATION (CONT..)
 Site: deep intramuscularly (IM) at anterolateral aspect of thigh
 Thiomersal (0.01%) - preservative
 Storage: - kept at 2–8oC; if accidentally frozen - discarded
 Dose: The usual dose (given to children) - 25 Lf units, adult
dose - 2 Lf units
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39. PROPHYLAXIS – VACCINATION (CONT..)
 Adult immunization:
 Td vaccine recommended for adults >18 years who have
completed their primary vaccination schedule - booster dose
once in every 10 years till the age of 65
 Adults who have not completed their primary vaccination
schedule: 3 doses of Td given at 0, 1 month, and 1 year.
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40. ADVERSE REACTIONS FOLLOWING DPT
ADMINISTRATION
 Mild - Fever and local reaction (swelling and indurations)
 Severe: Whole cell killed vaccine of B. pertussis is
encephalitogenic. Hence, DPT is not recommended after 7
years of age
 Absolute contraindication to DPT
 Hypersensitivity to previous dose
 Progressive neurological disorder
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41. DIPHTHEROIDS
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42. DIPHTHEROIDS
 Also called – Coryneform bacteria
 Nondiphtherial corynebacteria
 Normal commensals in throat, skin, conjunctiva
 Invasive disease in immunocompromised patients
42

43. DIPHTHEROIDS (CONT..)
 Differentiated from C. diphtheriae by many
features:
 Stains more uniformly than C. diphtheriae
 Palisade arrangement: Arranged in parallel
rows rather than cuneiform pattern
 Absence of metachromatic granules
(except C. xerosis).
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44. DIPHTHEROIDS (CONT..)
Coryneforms that are rarely pathogenic to man are:
 C. ulcerans and C.pseudotuberculosis produce diphtheria
toxin and cause localized ulcerations in throat
 C. ulcerans causes infections in cows. Human infections
may occur through cow's milk
 C. pseudotuberculosis (Preisz–Nocard bacillus) – Animal
pathogen. Human infection very rare.
44

45. DIPHTHEROIDS (CONT..)
Coryneforms that are rarely pathogenic to man are (Cont..):
 C. Minutissimum:
 Localized infection of skin (axilla and groin) ‘erythrasma’
 Wood’s lamp - emit coral red color
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46. DIPHTHEROIDS (CONT..)
Coryneforms that are rarely pathogenic to man are (Cont..):
 C. Jeikeium:
 Lipophilic, colonizes skin of hospitalized patients
 Can cause bacteremia, endocarditis and meningitis,
especially in immunocompromized
 Usually multidrug resistant, responds only to vancomycin
46

47. DIPHTHEROIDS (CONT..)
Coryneforms that are rarely pathogenic to man are (Cont..):
 C. Urealyticum
 Skin commensal, rarely causes urinary tract infection
(pyelonephritis) & alkaline encrusted cystitis (struvite stones
in alkaline urine) in immunocompromized
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