Medically important Bacteria: Part IV- Cornybacterium diptheriae

Introduction

Cornybacterium diptheriae is a slender gram-positive bacteria. It is usually club-shaped due to presence of volutin granules either on one or both of its poles. In stained conditions (Albert Staining), volutin granules appear bluish-black and are also called as Babes-Ernst Bodies.

Epidemiology

1) Diptheriae bacteria are distributed mainly in the areas which are overcrowded and level of vaccine induced immunity is low.
2) Sources of infection-Human carriers harbouring the bacteria in their oropharynx.
3) Transmission-Droplet infection by the human carriers upon sneezing, coughing etc.
4) Incidence-The bacteria attacks primarily children of age group within 12-15 years.

Determinants of Pathogenecity-

C. diptheriae primarily produce exotoxin, that too when it approaches its death phase in response to overpopulation of its own colony. The exotoxin produced consists of 2 fractions-

1) Fraction B- It serves for attachment of the exotoxin to the host cells. It attaches itself to the receptor named Heparin- binding Epidermal Growth Factor, that is expressed on many eukaryotic cells. It particularly binds to the myocardium and nerve cells, thus explaining the systemic effects of the toxin on Heart, Nervous System and Adrenal Medulla.
2) Fraction A- After the exotoxin has attached itself to the eukaryotic cell, the fraction B comes into play and produces the actual toxic effects of the toxin. It produces its toxic effect by causing ribolysation of Elongation Factor-2 (EF-2), thus inactivating the factor necessary for Protein Translation and hence blocks protein biosynthesis in the Host Cells.

Clinical Syndromes; Pathophysiology-

1) Local Effect- The bacterium initially colonizes over and inside the epithelial cells. The toxin produced causes necrosis of the inhabited and attacked epithelium. Slowly and gradually, a layer develops over the affected area (usually tonsil, larynx, pharynx or respiratory tract) consisting of Fibrinous Exudate, leucocytes, erythrocytes etc. Such membrane is called as Pseudomembrane. If one tries to peel off the pseudomembrane, it exposes the bleeding site underneath.

2) Systemic Effects- The systemic effects are characterized by cytopathic effects of Myocardium, Nervous System and/or Adrenal Glands, as already cited above.

Clinical Symptoms-

1) Initial symptoms are characterized by intense and severe pharyngitis and Laryngitis.
2) Pseudomembrane developed is usually black or Greyish-Black.
3) Pharyngeal Pseudomembrane at times becomes so severe that it even blocks the respiratory tract and causes suffocation in the patient.
4) Later on, the subject may experience difficulty in speech, swallowing, movement of extremities and Vision.

Treatment-

1) Treatment follows same lines as any other bacterial disease therapy. Antibiotics like Penicillin or erythromycin is commonly administered to eliminate the bacteria.
2) It also involves administration of Diptheria anti-toxin to a person. This anti-toxin neutralizes the Diptheriae exotoxin present in the patient. Administration of anti-toxin within the dose range of 20,000-1,00,000 U (depending on the severity of disease) is commonly followed.
3) Vaccination is another wise step as a method of prophylaxis against the bacterial disease.
4) Administration of Diptheriae toxoid is yet another step that may be followed. It comes in few different forms:
a) Formol Toxoid
b) Toxin-Anti-toxin combination
c) Alum precipitated Toxoid

Images' Links-

1) http://140.198.64.190/~johnson/labtools/Dbacyst/cdipth3.jpg
2) http://www.geocities.com/capecanaveral/3504/cdgm.jpg
3) http://traumwerk.stanford.edu/archaeolog/corynebacterium%20diptheriae.jp...