Which is the causative organism of diphtheria. Describe it’s morphology,
pathogenesis and lab. diagnosis.
Corynebacterium diphtheria
Definition
Corynebacterium diphtheriae is the bacteria which causes diphtheria
An aerobic Gram positive bacillus (rod shaped)
Morphology
Slender rods
Club shaped swelling at one or both ends.
Non-capsulate
Gram positive
Irregularly stained with granules
Non acid fast
Non-spore forming
Non motile
Has granules composed of polymetaphosphate
Stains with Loffler's methylene blue
Shows bluish purple metachromatic granules with polar bodies
Gravis is most virulent
Virus infected Corynebacterium diphtheriae produces Exotoxin
Corynebacterium diphtheriae gets killed at 58°C in 10 mt and at 100°C in 1mt
Survives in blankets, floordust, toys and other inanimate objects
Biotypes
- Corynebacterium diphtheriae - gravis - produces most serious hemorrhagic paralytic complications - epidemic
- Intermedius - hemorrhagic
- Mitis - obstructive complications
Pathogenesis
Disease Caused : Diphtheria - acute toxin mediated disease
An infection of local tissue of the upper respiratory tract
Enters the throat tissues - multiplies - produces exotoxin -
Incubation period 3to 4days/one day.
May affect the epithelia of pharynx, nasal.laryngeal, otic.otic.conjunctiva. genital.vulva -
May cause Malignant severe toxemia, Lymphadenitis of the neck causing Bull neck and circulatory failure due to carditis, epistaxis, purpura, general bleeding tendency, asphysia, pneumonia,septicshock, otitismedia,toxemia, endocarditis, meningitis,cerebralabscess
The toxin produced by the bacteria affects heart and peripheral tissues - life threatening
Exotoxin causes necrosis of the epithelial cells, kills neutrophils and liberates serous serous and fibrinous material forming a grayish white pseudo membrane
The membrane bleeds on being dislodged
Surrounding tissue is inflamed (red) and edematous.
produces pharyngitis and cutaneous lesions if the infection occurs in the skin
Diphtheria toxin binds to the host cells and interrupts the protein of the cell and it results in cell death
Staining methods
Gram's method
Albert's stain
Neissers stain
Ponders stain
Culture Media
Needs enrichment media which contains blood, serum or egg
Commonly used mediums are Loeffler serum slope, tellurite blood agar, Hoyles medium
On culturing : colonies develop which are dark -
Loffler serum slope - grows rapidly in 6-8 hours - smal opaque disks which turns yellow
Tellurite blood agar - contains tellurite which inhibits other bacteria - grey/black colonies
Diagnosis
Collection of specimen
Throat swabs
Smear examinations
Gram's staining
Immunofluorescent methods
Cultures onLoeffers serum slope, Tellurite blood agar, Blood agar
Virulence tests : in vivo can be done on animals or in vitro
Toxigenicity tests : in vitro Elek test in vivo animal inoculation - inoculation : rabbit skin test (Necrosis), guinea pig challenge test - lethal
Epidemiology
Eradicated in developed nations -
Affects children between 2- 5 yrs - asymptomatic carriers +
Spreads by person to person contact
Prophylaxis
Immunization
Active - toxoid - attenuated bacteria which acts as antigen to produce antibodies in the body - DPT - Triple vaccine (Diphtheria, pertussis, tetanus)
- three doses of DPT Primary immunization - three doses at least 4 weeks apart - booster doses given between
3 and 5 yrs of age
Passive - antitoxin
Both active and passive given for acute cases
herd immunity - develops in the community later
Antibiotic Sensitivity
Sensitive to penicillin erythromycin
In acute infection in addition to antibiotics an antitoxin is also needed
vaccine - toxoid - prepared by treating the bacteria with formalin Toxoid
Antitoxin is made from diphtheria toxin, The toxin is inoculated to an animal and the antibodies to the toxin (serum) from the animal can be used as a vaccine
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