Bordetella

Bordetella is a genus of obligate aerobic, Gram-negative coccobacilli. They are highly fastidious and difficult to isolate. The most important pathologic species is Bordetella pertussis (B. pertussis), which is commonly isolated on Bordet-Gengou agar. Bordetella pertussis is highly infectious via respiratory droplets and is only known to infect humans, causing the clinical syndrome of pertussis. Pertussis is characterized by 3 distinct phases: catarral, paroxysmal, and convalescent. Pertussis is rare in developed countries due to widespread use of the diphtheria, tetanus, and acellular pertussis (DTaP) combined vaccine.

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General Characteristics

Basic features of Bordetella

  • Gram-negative coccobacilli
  • Encapsulated
  • Non-motile
  • Non-spore forming
  • Obligate aerobes

Biochemistry and growth

  • Very fastidious
  • Do not ferment carbohydrates
  • Inhibited by fatty acids (need media that absorb the fatty acids to grow)
  • Difficult to culture; isolated on: 
    • Bordet-Gengou agar (blood, potato extract, and glycerol plus antibiotics and nicotinamide)
    • Regan-Lowe medium (charcoal with defibrinated horse blood)

Pathogenic species

  • B. pertussis (most important): causes pertussis (whooping cough)
  • B. parapertussis: can also cause pertussis
  • B. bronchiseptica: rare in humans, but can infect immunocompromised hosts 

Bordetella Pertussis

Epidemiology

  • Incidence worldwide: 24 million cases per year
  • Deaths worldwide: approximately 161,000 per year
  • Incidence in the United States: 15,000 cases in 2018
  • Vaccination reduces the incidence significantly in young children, but does not confer lifelong immunity.
  • Cyclical epidemics occur every 2–5 years.
  • Disease is less severe in adolescents and adults than in young children.

Transmission

  • No known environmental reservoirs
  • Transmitted by respiratory droplets
  • Many household contacts can have asymptomatic or very mild disease, frequently undiagnosed.
  • Incubation period is 1 to 3 weeks (most commonly 7–10 days).

Pathophysiology

Pathogenesis:

  • The 1st step is inhalation.
  • Bacteria adhere to the ciliated epithelium of the nasopharynx and upper respiratory tract by various protein adhesins.
  • Cause tissue damage and loss of protective epithelial cells by toxin production
  • Results in microaspiration and cough
  • Fatal cases are associated with:
    • Necrotizing bronchiolitis
    • Alveolar hemorrhage
    • Fibrinous edema
    • Intracellular bacteria in alveolar macrophages and ciliated epithelium (evade intracellular digestion)

Virulence factors:

  • Filamentous hemagglutinin pili:
    • Allow for attachment to ciliated, respiratory epithelium
  • Pertussis toxin (A/B toxin):
    • Ribosylates (inhibits) guanine nucleotide-binding protein (Gi)
    • Increases cyclic adenosine monophosphate (cAMP)
    • Impairs phagocytosis
    • Causes lymphocytosis
  • Adenylate cyclase toxin:
    • Increases cAMP similar to the Bordetella anthracis EF-2 toxin
    • Induces apoptosis of macrophages
  • Tracheal toxin:
    • Induces nitric oxide gas production
    • Damages respiratory epithelium

Clinical presentation

  • Pertussis is a form of bronchitis.
  • In children, classically has 3 stages:
    • Catarrhal stage: congestion, coryza (runny nose), conjunctivitis, low-grade fevers (1–2 weeks)
    • Paroxysmal stage (2–8 weeks):
      • Severe coughing episodes on expiration
      • “Whoops” on inspiration (whooping, paroxysmal cough
      • Post-tussive vomiting
      • In infants, often presents with apnea instead of coughing paroxysms
    • Convalescent stage: decreased frequency of coughing (4 weeks to months)
  • In adults and adolescents:
    • Often milder than in children
    • Prolonged cough (> 2 weeks) is frequently the only symptom.
    • Also known as the “100-day cough” 

Chest radiograph of an 11-year-old patient with Bordetella pertussis infection
Reinforcement of the perihilar bronchovascular reticulum and heterogeneous infiltrates on the inferior third of both lung fields.

Image: “Bordetella pertussis an agent not to forget: a case report.” by Melo N, Dias AC, Isidoro L, Duarte R. License: CC BY 2.0

Identification

Specimen collection:

  • Nasopharyngeal swab or aspiration
  • Cotton-tipped swabs should not be used because they contain fatty acids toxic to B. pertussis.
  • Polyester or calcium alginate swabs should be used instead.
  • Specimen should be obtained from the posterior nasopharynx.

Tests:

  • Culture (on special media)
  • Polymerase chain reaction (PCR)
  • Serology: primarily research applications

Prevention

  • Acellular vaccine
  • Component of the diphtheria, tetanus, and acellular pertussis (DTaP) combined vaccine

References

  1. Cornea P., & Lipsky B. (2020). Pertussis infection: Epidemiology, microbiology, and pathogenesis. UpToDate. Retrieved January 4, 2021, from https://www.uptodate.com/contents/pertussis-infection-epidemiology-microbiology-and-pathogenesis?search=bordetella&source=search_result&selectedTitle=4~41&usage_type=default&display_rank=4
  2. Cornea P., & Lipsky B. (2020). Pertussis infection in adolescents and adults: Clinical manifestations and diagnosis. UpToDate. Retrieved January 4, 2021, from https://www.uptodate.com/contents/pertussis-infection-in-adolescents-and-adults-clinical-manifestations-and-diagnosis?search=bordetella&source=search_result&selectedTitle=1~41&usage_type=default&display_rank=1
  3. Guiso N. (2015). Bordetella pertussis. In Nicholson LK, & Janoff EN. (Eds.), Mucosal Immunology (4th ed.) https://www.sciencedirect.com/topics/medicine-and-dentistry/bordetella-pertussis

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