Corynebacteria
These are gram positive bacilli that are found in soil, skin and mucus membrane.
Corynebacteria are made up of two main species;
1. Corynebacterium diphtheriae
2. Diphtheroids
Most pathogenesis species are facultative anaerobes but commensals (diphtheroids) grow aerobically.
1. Corynebacterium diphtheriae
Cause diphtheria
Gram positive, club shaped bacilli.
Size; 0.3-0.8 micrometre in diameter.
1.5-8.0 micrometre in length
Characteristics
Grow in media enriched with egg, blood or serum.
It is facultative anaerobes.
Grow at optimum temperature 37 degree Celsius and PH 7.5
Produce exotoxin.
It is non motile, noncapsulated, club shaped gram positive bacilli.
Source and Mode of Transmission
Corynebacterium diphtheriae are found in throats and nasopharynx of carriers.
Transmitted through respiratory droplets
By direct contact
Through contaminated fomites
Pathogenesis
1. Upper respiratory tract infection
Infection in throat
Neuritis of cranial nerve; inflammation of PNS.
Paralysis of muscle
Swelling if lymph node in neck
Malignancy
Septic; leads formation of ulceration
Hemorrhage
Types of Diphtheria
Diphtheriae may be following clinical type depending up the site of Infection;
1. Nasal diphtheria
2. Pharyngotonsillar diphtheria
3. Laryngotracheal diphtheria
4. Cutaneous diphtheria; mainly around mouth and nose
5. Conjuctival diphtheria
6. Respiratory diphtheria
7. Faucial diphtheria; infection is limited mostly to the tonsillar region.
8. Otitic diphtheria
Laboratory diagnosis
Collection of specimen and transport
Throat swab
Direct microscopy
Appear gram positive club shaped bacilli are seen.
Arrangement rod shaped bacilli (Chinese letter arrangement)
Culture
Grows on enrich media; serum broth, blood medium, serum
Colony morphology and Staining
Biochemical reaction
Cultures bacilli colonies ferment glucose and maltose with acid production only.
Treatment
Treatment is given with antibiotics, like penicillin, rifampin or erythromycin help in reducing load of bacteria and prevent further production of toxin.
Prevention
Diphtheria is prevented only by immunization with toxoid. It is commonly administered in DPT; triple vaccine, together with tetanus toxoid and pertussis antigens.
Avoid contact with infected person.
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