Corynebacterium spp Flashcards
What are the bacteriological features of Corynebacterium spp?
• Gram-positive aerobic bacillus
– arranged in V or L shapes or like “Chinese letters”
– metachromatic granules seen on Albert’s stain
– Aerobic / facultative anaerobic
– Catalase positive
– non-spore forming
– Ubiquitous in plants and animals;
• colonise skin*, upper respiratory tract & genito-urinary tract
What are the important species of Corynebacterium?
• Corynebacterium diphtheriae- From the Greek “diphtheria” (leathery skin)
– Diphtheria
• C. jeikeium
• C. ulcerans
• C. haemolyticum - now known as Arcanobacterium haemolyticum
• C. minutissimum
What is the epidemiology of Corynebacterium diphtheriae?
- The organism has a worldwide distribution, humans are the only known reservoir
- Prior to vaccination, significant cause of nursery deaths (need 85% immunisation rate)
- At risk: children/unvaccinated/overcrowding
- Reservoir: Cases and asymptomatic carriers
- Spread is by droplet
- Nasal carriers may shed for weeks
- Reduced incidence with immunization programs
What are the biotypes of Corynebacterium diphtheriae?
There are 3 biotypes (based on colonial appearance and biochemical profile)
• C. diphtheriae gravis
• C. diphtheriae intermedius*
• C. diphtheriae mitis
- this biotype is rarely associated with disease
What is the diphtheria toxin?
- The disease diphtheria is caused by exotoxin secreted by the bacteria at the site of infection
- Not all strains produce toxin
- The toxin produced is identical in all 3 strains
- Toxigenicity can be demonstrated by the Elek test or by PCR for the tox gene
What are the manifestations of C. diphtheriae infection?
Manifestations of C. diphtheriae infection
• Clinical disease
-Respiratory
-Cutaneous
• Asymptomatic carrier stateWhat are the clinical features of Diphtheria?
Diphtheria: Clinical Features
• Incubation period 2-6 days (range, 1-10 days)
• May involve any mucous membrane, or skin
• Classified based on site of infection
-Anterior nasal
-Tonsillar and pharyngeal
-Laryngeal
-CutaneousWhat are the symptoms of Pharyngeal and Tonsillar Diphtheria?
Pharyngeal and Tonsillar Diphtheria
• Insidious onset of exudative pharyngitis
• The inflammation and exudate spread over 2-3 days and may form a thick adherent pseudomembrane (gray - green - black)
• The pseudomembrane may cause respiratory obstruction
• The pseudomembrane composed of exudate, bacteria, fibrin, dead cells, plasma cells and lymphocytes
Low-grade fever
• The patient appears “toxic”
• Toxin is absorbed and causes damage to distant organs (heart, nervous system & kidneys/adrenals)
Pharyngitis/tonsillitis
the infected person may develop “bull neck” - oedema and tenderness over anterior tissues of neck and local lymphadenopathy
What are the complications of Diphtheria?
• Most attributable to toxin
• Severity of complications= related to extent of local disease
• Most common complications
- Myocardial
-Neuritis
• Death occurs in 5%-10% from respiratory obstruction, cardiac arrhythmia, respiratory paralysis
What is the diagnosis of Diphtheria?
• Clinical
– History: travel, vaccination
– Severe exudative tonsillitis
• Nasal/ Throat/ Pharyngeal swab culture
– selective media, e.g., Loeffler’s Serum slope or Potassium Tellurite agar
– PCRWhat is Diphtheria culture?
Diphtheria culture
Potassium Tellurite or Cysteine-tellurite agar:
inhibitory selective media – tellurite prevents overgrowth with normal flora
growth takes up to 48 hours
Corynebacterium diphtheriae reduces tellurite to produce classical gray/black or brown colonies
What is the management of Diphtheria ?
• Diphtheria antitoxin
• Antibiotics - penicillin / erythromycin
• Airway management/ ECG & enzymes/ Neuro
• Droplet precautions
• Notifiable infection- contacts
• Follow-up:
– Cultures to ensure eradication.
– Diphtheria toxoid immunization during their convalescence since natural infection does not reliably induce immunity
What is Diphtheria Antitoxin?
• It is used only for treatment of diphtheria, not prophylaxis
• Antitoxin neutralizes only unbound toxin
• It is produced in horses
(10% risk of hypersensitivity/serum sickness)
What is Cutaneous Diphtheria?
Cutaneous Diphtheria
• May enter through a break in the skin after contact with an infected person
• May form a “papule” – a chronic non- healing ulcer - which may be covered by a gray membrane
• +/- systemic disease, secondary to effects of toxin
What are the methods of prevention of diphtheria?
• Immunisation: diphtheria toxoid, in the routine immunisation schedule in many countries
