General characteristics and morphology
The causative agents of whooping cough (Bordetella pertussis) and parapertussis (Bordetella parapertussis) are bacteria that cause human respiratory tract infections. Historically, the whooping cough bacillus was discovered in 1906 by J. Bordet and O. Gengou. The bacteria belong to the family Alcaligenaceae.
Morphologically, they are very small Gram-negative rods (coccobacilli). They are non-motile and possess a microcapsule. When stained with toluidine blue, bipolar granules can be observed, which are lipoid accumulations that stain metachromatically.
Cultural properties
Bordetellae are obligate aerobes. The causative agent of whooping cough (B. pertussis) is extremely fastidious regarding nutrient media. Its growth requires complex media supplemented with adsorbents (blood, charcoal) because the bacterium releases toxic metabolites that inhibit its own growth. Classic media include:
- Bordet-Gengou medium (containing blood, potato, and glycerol).
- CUA (casein-charcoal agar).
On Bordet-Gengou medium, colonies of B. pertussis appear as small, shiny "drops of mercury" or "pearls". Species of B. parapertussis and others are less fastidious, grow faster, and can be cultured on simple media (e.g., nutrient agar).
Pathogenicity factors
The pathogenicity of bordetellae is due to adhesion factors and toxin production:
- Adhesins: The main role is played by filamentous hemagglutinin, which binds to glycolipid receptors on epithelial cilia. Pili, pertactin, and capsular agglutinogens are also involved.
- Pertussis toxin: Specific to B. pertussis. It ribosylates the G protein, causing uncontrolled cAMP synthesis, which leads to systemic effects (lymphocytosis, histamine sensitization).
- Tracheal cytotoxin: Causes ciliostasis (cessation of ciliary beating) and epithelial necrosis.
- Adenylate cyclase hemolysin: Protects bacteria from phagocytosis.
Epidemiology and prevention
Whooping cough is a strict anthroponosis. The transmission mechanism is airborne droplet. The infection is extremely contagious (index 0.75–0.9), especially in the catarrhal period. The disease poses the greatest danger to infants under one year of age.
For prevention, DTP vaccine is used — an adsorbed diphtheria, tetanus, and pertussis vaccine containing killed B. pertussis cells. Acellular vaccines containing purified antigens are also used; they are less reactogenic but provide less durable immunity.
Briefly: answers to topical questions
What stages are distinguished in the clinical course of whooping cough?
The clinical course of whooping cough has three consecutive stages. The first is the incubation period, which lasts about two weeks. The second is the catarrhal period, accompanied by a mild cough, sneezing, and low-grade fever, during which the patient is maximally contagious. The third is the paroxysmal or spasmodic period, characterized by paroxysmal coughing with a whooping sound, accompanied by severe hypoxia, vomiting, and convulsive syndrome.
Which specific antigens are part of the acellular pertussis vaccine?
The acellular pertussis vaccine contains five specific components isolated from Bordetella pertussis. These include pertussis toxoid, filamentous hemagglutinin, pertactin, and type 2 and type 3 fimbriae.
What laboratory diagnostic methods are used for whooping cough?
Laboratory verification of whooping cough involves bacteriological methods consisting of inoculating material obtained via swab or cough plate method. Rapid diagnostics include detecting B. pertussis antigens or DNA in nasopharyngeal mucus using immunofluorescence assay or polymerase chain reaction. Retrospective diagnostics in later stages are based on serological reactions such as CFT, indirect hemagglutination assay (IHA), and ELISA.
Class and exam questions
How do the growth requirements of the whooping cough and parapertussis pathogens differ?
The causative agent of whooping cough (B. pertussis) grows only on complex media with adsorbents (Bordet-Gengou medium, CYE agar). The parapertussis bacillus (B. parapertussis) is less fastidious and capable of growing on simple media such as nutrient agar.
What is the essence of R-S transformation in bordetellae?
When cultured outside the body, bordetellae transition from the virulent S-form (phase I), which produces toxins, to the avirulent R-form (phase IV) due to the loss of surface antigens.
How does pertussis toxin work?
The toxin penetrates the cell and ribosylates the regulatory G protein, leading to unabated cAMP synthesis and disruption of cellular functions in the respiratory tract.
What else to study on this topic
- Biochemical activity and differential diagnostics of species
- Mechanisms of genotypic and phenotypic variability
- Pathogenesis of whooping cough and stages of the disease
- Mechanisms of specific immunity
- Methods of microbiological diagnostics of whooping cough
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