Bordetella: Introduction, Morphology, Pathogenecity, Lab Diagnosis,Treatment and Prevention

Bordetella was described by Bordet and Gengou (1900) in a sputum sample of children with whooping cough. In 1906 -B. pertussis ( Whooping cough) 1911 - B. bronchoseptica from dog 1937 - B. parapertussis ( mild whooping cough)

Introduction of Bordetella

Bordetella was described by Bordet and Gengou (1900) in a sputum sample of children with whooping cough. B. pertussis is the causative agent of pertussis or whooping cough.

In 1906 –B. pertussis ( Whooping cough)

1911 – B. bronchoseptica from dog

1937 – B. parapertussis ( mild whooping cough)

Morphology of Bordetella

Bordetella pertussis:

Gram- ve  coccobacilli, 1-1.5 × 0.5 μm, may occur singly or in the chain and may show bipolar staining, non – motile, non – sporing, and capsulated.

B. parapertussis :Non- motile , Gram -negative bacilli.

B.bronchoseptica: similar with B. pertussis except it is motile.

B. pertussis: Same as parapertussis

Pathogenicity of Bordetella

Whooping cough due to irritation caused by endotoxin

The incubation period is most commonly 7 to 10 days.

Complication :

  • Lung damage with emphysema ( Pathological accumulation of air in tissue and  organs.)
  • Bronchopneumonia and bronchiectasis
  • Subconjunctival hemorrhage
  • Deafness

Virulence factors:

1 –   Heat labile toxin: causes vasoconstriction in the respiratory tract.

2- Tracheal cytotoxin ( CTC): derived from peptidoglycan of cell wall which inhibits DNA synthesis in ciliated cells.

3- Endotoxin LPS:

4- Pertussis toxin (PT):  controlled by PT gene. Mol. wt. 117000, stimulates cyclic  AMP pathway,  leading to over secretion.

5- Adenylate cyclase ( AC):

  • Present on the surface of the B. pertussis cell wall.
  • Inhibits the phagocytic activity of the host cell.

Mechanism:

Enzyme enters into the cell and gets activated by a mammalian protein called- Calmodulin. Activated A adenylate cyclase induces a high level of intracellular  CAMP which impairs the bactericidal activity of polymorphonuclear neutrophil ( PMN) and Macrophages.

6- Haaemolysin: cause hemolysis

7- Filamentous haemagglutination: Agglutination to RBC is inhibited by cholesterol shake culture does not cause filamentous haemagglutination.

Laboratory diagnosis of Bordetella

Specimen: B.pertussis colonizes the ciliated epithelial cells in the upper and lower respiratory tract. A culture specimen should therefore be obtained from the surface of the respiratory epithelial cells of the upper respiratory tract. Specimens obtained from the throat, sputum, or anterior nose that are not lined with ciliated epithelium are not adequate.

Nasopharyngeal secretion

Nasopharyngeal swab or aspiration

Asking patients directly to cough into the selective medium.

Direct  microscopic examination :

Gram’s stain:  Gram-negative bacilli as described above.

Transportation Medium: Transferred to Casamio acid solution at pH 7.2 in modified  Stuarts medium Glycerin potato blood agar Bordet Gengou. The addition of penicillin is more selective.

Culture

Selective media:

Cephalexin Charcoal Blood Agar

Bordet- Gengou’s medium

2-6 days incubation at 37°C

Colony

Small, raised, shiny

Mercury or dewdrop appearance

Biochemical test:

species                   Motility, Blood agar,   Urea, Oxidase, Catalase

B.pertussis         –          –                       –               +                +

B.parap                  –        +                 +/24h      –                 +

B.bronchoseptica        +        +            +4h          +                 +

Serology

Based on common surface antigen, there are 3 serotypes of B. pertussis.

Suitability of IgM, IgA, and IgG antibodies for diagnosis

Molecular Test

Detection of B. pertussis by PCR

Antimicrobial Sensitivity  Testing (AST)

Following antibiotics are useful for AST-

  • Erythromycin
  • Chloramphenicol
  • Tetracycline
  • Cotrimoxazole

Epidemiology

Pertussis is a very contagious disease that causes uncontrollable coughing with little or no fever. The coughing may be so severe that it leads to vomiting and aspiration. Whooping cough is predominantly a pediatric disease. It is common in the first year of life and maternal antibodies are not protective. It is worldwide in distribution. Epidemics occur periodically. In the early stage of infection droplets and fomites contaminated by oropharyngeal secretion are infective.  Nonimmune easily catches the infection and household contacts at risk.  B. pertussis is only responsible for 95 % of cases, B. parapertussis , 5%, and  B. brochoseptica occasionally occur. Sometimes adenovirus, Mycoplasma pneumoniae may mimic whooping cough.

Prevention of Bordetella

In view of the high incidence and severity of the new-born disease, it is advisable to start immunization as soon as possible. Three injections at intervals of 4-6 weeks should be given before the age of six months, followed by a booster at the end of the first year of life. Children under four years of age who are patient contacts should receive a booster even if they have been previously immunized.

Vaccine: Diphtheria Pertussis and Tetanus (DPT)

 

Further Reading

  1. https://www.ncbi.nlm.nih.gov/books/NBK7813/
  2. https://cmr.asm.org/content/18/2/326
  3. https://cmr.asm.org/content/28/4/1005
  4. http://www.antimicrobe.org/b83.asp
  5. https://academic.oup.com/cid/article/47/3/328/314351
  6. https://www.cdc.gov/pertussis/about/diagnosis-treatment.html
  7. https://www.elsevier.com/books/molecular-medical-microbiology/tang/978-0-12-397169-2
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