Bordetella

Bordetella are gram-negative cocobacilli, in human they colonize mainly the ciliated epithelium of the upper respiratory tract. Human pathogens include B. pertussis and B. parapertussis – they cause pertussis or parapertussis. The other B. bronchoseptica, B. avium, B. hinzii, B. holmesii and B. trematum.

B. Pertussis on soil (agar supplemented with Cephalexin)

Bordetella pertussis

Bordetella pertussis is a short, immobile rod with an ovoid shape. It has a unique ability to colonize epithelial cilia in the airways. B. pertussis is a human pathogen. It is the cause of whooping cough, which was considered one of the most serious diseases of infants and children until vaccination was introduced.

Morphology

• ovoid stationary rod
• gram-negative

Physiology

• strictly aerobic, immobile, non-sporulating
• requires enriched soils

Cultivation

• the suitable culture medium is Bordet-Gengou medium, agar with defibrinated rams blood, potato infusion, and glycerol
• colonies grow after 36-72 hours, are small, translucent with a pearlescent luster and a narrow hemolysis zone around them

Laboratory diagnosis

• nasopharyngeal swab, first the swabs are rinsed with a drop of penicillin to prevent the growth of gram-positive microorganisms, and then spirally inoculated on Bordet-Gengou soil
• identification by agglutination with a specific antiserum, agglutination, precipitation antibodies can be detected within three weeks

Antigens and toxicity

B. pertussis produces immunologically and pathophysiologically unique responses in the macroorganism. Most of these effects are caused by pertussis toxin (PT).

• Pertussis toxin is composed of two types of subunits A (active enzyme) and B (binding subunit). The A-subunit is an ADP-ribosyl transferase that transfers the ADP-ribosyl portion of NAD to the membrane-bound regulatory protein. This protein physiologically inhibits adenyl cyclase, resulting in stimulation by toxin inactivation.
• Pertussis toxin causes hypoglycemia by stimulating insulin production. PT also increases histamine sensitivity and enhances capillary permeability.
• B. pertussis produces a lethal toxin (dermonecrotic toxin) causing local necrosis after intradermal injection.
• Another product is a tracheal cytotoxin, which is toxic to the ciliated airway epithelium.

Pathogenesis

B. pertussis adheres to the mucosal surface of the trachea and bronchi, where it rapidly multiplies and blocks cilia function. Residues of microorganisms contain a toxin that is released and irritates the mucous membranes, induces lymphocytosis, and causes catarrhal inflammation to necrosis of the mucosal epithelium. However, the bordetella do not get into the bloodstream. Due to the blockage of mucociliary transport, peribronchitis and an irritating cough develop.

Disease

• Pertussis (whooping cough)

Treatment

Hyperimmune immunoglobulin can be used for children under the age of two at an early stage of the disease. Antibiotic therapy reduces acute toxicity and prevents pulmonary complications, chloramphenicol is given. Erythromycin or ampicillin are suitable.

Prevention

Vaccination is in the Czech Republic since 1958. Since 2007 as a part of hexavaccine.

Bordetella parapertussis

B. parapertussis is a strictly aerobic bacterium, the special soil for cultivation is Bordet-Gengou soil (it contains potato extract with glycerin and 25% ram's blood), it also grows on blood and chocolate agar and on MacConkey soil. It is less demanding in terms of culture than B. pertussis , colonies are characterized by pronounced beta-hemolysis and a dark brown pigment. 

The bacterium is oxidase-negative and urease-positive. Unlike B. pertussis, it does not form a pertussis toxin and also differs from it in its antigenic equipment. 

B. parapertussis is the causative agent of parapertussis (whooping cough syndrome). The disease is very similar to pertussis , the difference is mainly in the duration of cough, which is 31 ± 18 days for parapertussis, while it is 23 ± 11 days for pertussis. The route of transmission is droplets of infected aerosol, the incubation period is 7–10 days, the disease then takes place in three stages (catarrhal, paroxysmal and convalescent). Bordetella adhere to the ciliated epithelium of the airways, where they multiply, impair the function of the cilia and damage the mucosa. 

Macrolides (clarithromycin, azithromycin) are the drug of choice in therapy , and tetracyclines, co-trimoxazole or chloramphenicol are also effective. The treatment should last for 14 days. 

Vaccination against B. pertussis does not protect against B. parapertussis infection.

References 

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