| Bordetella pertussis | |
|---|---|
| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Beta Proteobacteria |
| Order: | Burkholderiales |
| Family: | Alcaligenaceae |
| Genus: | Bordetella |
| Species: | B. pertussis |
| Binomial name | |
| Bordetella pertussis (Bergey et al. 1923) Moreno-López 1952 |
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Bordetella pertussis is a Gram-negative, aerobic coccobacillus capsulate of the genus Bordetella, and the causative agent of pertussis or whooping cough. Unlike B. bronchiseptica, B. pertussis is non-motile. Its virulence factors include pertussis toxin, filamentous hæmagglutinin, pertactin, fimbria, and tracheal cytotoxin.
There does not appear to be a zoonotic reservoir for B. pertussis—humans are its only host.
The bacterium is spread by airborne droplets. The incubation period is 7–14 days.
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Pertussis (or whooping cough) is an infection of the respiratory system and characterized by a “whooping” sound when the person breathes in, although only 50% of patients display the classic "whooping" sound as they attempt to draw breath over a partially closed glottis. In the US it killed 5,000 to 10,000 people per year before a vaccine was available. Vaccination has transformed this and between 1985-88 fewer than 100 children died from pertussis. Worldwide in 2000, according to the WHO, around 39 million people were infected annually and about 297,000 died. A graph is available showing the dramatic effect of introducing vaccination in England.[1]
Bordetella pertussis infects its host by colonizing lung epithelial cells. The bacterium contains a surface protein, filamentous hemagglutinin, which binds to sulfatides that are found on cilia of epithelial cells. Once anchored, the bacterium produces tracheal cytotoxin, which stops the cilia from beating. This prevents the cilia from clearing debris from the lungs, so the body responds by sending the host into a coughing fit. These coughs expel some bacteria into the air, which are free to infect other hosts.
Bordetella pertussis has the ability to inhibit the function of the host's immune system. The toxin known as pertussis toxin (or PTx) inhibits G protein coupling that regulates adenylate cyclase (CyaA) mediated conversion of ATP to cyclic AMP. The end result is that phagocytes convert too much ATP to cyclic AMP, which can cause disturbances in cellular signaling mechanisms, and prevent phagocytes from correctly responding to an infection. PTx, formerly known as lymphocytosis-promoting factor, causes a decrease in the entry of lymphocytes into lymph nodes. This can lead to a condition known as lymphocytosis, with a complete lymphocyte count over of 4000/μL in adults or over 8000/μL in children.
The infection occurs most with children under the age of one when they are unimmunized or children with faded immunity, normally around the age 11 through 18. The signs and symptoms are similar to a common cold: runny nose, sneezing, mild cough, and low-grade fever. The patient becomes most contagious during the catarrhal stage of infection, normally 2 weeks after the coughing begins. It may become airborne when the person coughs, sneezes, or laughs. Pertussis vaccine is part of the DTaP (diphtheria, tetanus, acellular pertussis) immunization. The paroxysmal cough precedes a crowing inspiratory sound characteristic of pertussis. After a spell, the patient might make a “whooping” sound when breathing in, or vomit. Adults have milder symptoms, like prolonged coughing without the “whoop.” Infants less than 6 months may not have the typical whoop. A coughing spell may last a minute or more, producing cyanosis, apnoea and seizures. However, when not in a coughing fit, the patient does not experience trouble breathing. This is because Bordetella pertussis inhibits the immune response and therefore very little mucus is generated in the lungs. A prolonged cough may be irritating and sometimes a disabling cough may go undiagnosed in adults for many months.
A nasopharyngeal or an oropharynx swab is sent to the bacteriology laboratory for Gram stain (Gram negative, coccobacilli, diplococci arrangement), growth on Bordet-Gengou agar or BCYE plate with added cephalosporin to select for the organism, which shows mercury-drop-like colonies.
The organism is oxidase positive, but urease, nitrase, and citrate negative. It is also non-motile.
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