Bordetella pertussis

Morphology

• Gram negative
• Coccobacillus
• Capsulated
• Non-motile
• Bipolar metachromatic granules are present.
• It is a strict human pathogen

Culture

• Strict aerobe
• Bordet-Gengou glycerine potato-blood agar medium is commonly used.
  • Contains a high percentage of blood (20%–30%) to inactivate inhibitors in the agar.
• Incorporation of diamidine fluoride and penicillin (Lacey’s DFP medium) makes it more selective.
• Transport media   ?    Modified stuart’s medium
• Mischulow’s charcoal agar
• Produces bisected pearls or mercury drops colonies.
• Confluent growth present and “aluminium paint” appearance.
• Culture films has Thumbprint appearance

Virulent Factors
1. Pertusis toxin

• Exotoxin 
• A and B subunits.
• B subunit
  •  binds to the target cells 
• A subunit
  •  acts on the target.
• Toxin itself gets activated by glutathione and ATP.
• Activated toxin ,activates cell membrane bound G proteins.
• Catalyzes the ADP ribosylation of the G proteins and activates them.
• The activated G protein in turn activates adenylate cyclase
• This results in an outpouring of cAMP which activates protein kinase and other intracellular messengers.

2. Filamentous hemagglutinin (FHA) secreted protein:

• Piracy of Adhesins
  • PT + FHA
  • Promotes secondary infection
  • By coating H. influenza and pneumococci so that they bind.

3.Tracheal cytotoxin

• Responsible for destruction of :
  • Ciliated cells respiratory epithelial cells.

4. Other virulence factors:

• Surface adhesins 
• Adenylate cyclase
• hemolysin
• LPS endotoxin
• pertactin agglutinogens 

Pathogenesis

• Infection is initiated by attachment of the organism to the ciliated epithelial cells of the nasopharynx
• Attachment is mediated by surface adhesions.
• Infection limited to respiratory mucosa only
• Local cellular invasion with intracellular persistence (systemic dissemination not occur).
• Systemic manifestation is due to toxin.
• Both cellular and humoral immunity are important.
• First defence is by antibody which prevents attachments of bacteria.
• Neurologrcal manifestation are due to hypoxia.

Test for checking pathogenicity

• Produced experimentally in several species of animals, the white mouse is most often employed.
• Intranasal inoculation produces a patchy interstitial pneumonia.
• Intraperitoneal inoculation of large doses is fatal due to toxaemia.
• Intracerebral inoculation causes a fatal infection. Immunized mice are protected. This forms the basis for 
• intracerebral mouse potency assay for pertussis vaccines.

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