Bordetella pertussis

Bordetella pertussis is a specific type of bacterium that causes pertussis. This disease is commonly known as whooping cough. It is a Gram-negative, aerobic, and encapsulated coccobacillus. Being aerobic means it requires oxygen to grow and sustain itself. It is also an obligate human pathogen. This means humans are the only known reservoir for the bacteria. Despite widespread vaccination, it still causes illness and death globally. This happens because of declining immunity or pathogen adaptation.

The infection process begins when the bacteria enter the respiratory tract. They travel through airborne droplets when a person coughs or sneezes. The incubation period averages 7 to 10 days. However, the range can be anywhere from 6 to 20 days. To stay in the body, the bacteria must attach to the host. They use specialized surface proteins to bind to ciliated epithelial cells. These proteins include filamentous haemagglutinin, pertactin, and fimbriae. Once anchored, the bacteria release several virulence factors. These factors include pertussis toxin, adenylate cyclase toxin, and tracheal cytotoxin.

These toxins disrupt the normal functions of human cells. Tracheal cytotoxin stops the cilia from beating. Cilia are the tiny hairs that clear debris from the lungs. When they stop working, the body responds with intense coughing fits. The pertussis toxin also interferes with the immune system. It inhibits G protein coupling in certain cells. This causes phagocytes to convert too much ATP into cyclic adenosine monophosphate. This disruption prevents phagocytes from responding correctly to the infection. It also limits how neutrophils migrate to the lungs. This can lead to lymphocytosis, where lymphocyte counts become very high.

Bordetella pertussis belongs to a genus containing nine different species. These species include B. parapertussis, B. bronchiseptica, B. avium, and B. hinzii. Other species are B. holmesii, B. trematum, B. ansorpii, and B. petrii. B. pertussis, B. parapertussis, and B. bronchiseptica form a closely related group. B. parapertussis causes a disease similar to whooping cough. B. bronchiseptica infects many different mammal hosts. It can cause a wide spectrum of respiratory disorders. While B. pertussis is normally nonmotile, it can sometimes express a flagellum-like structure. This is a similarity it shares with B. bronchiseptica.

Humans have studied this disease for many centuries. A French physician named Guillaume de Baillou described it after 1578. Some believe it was described even earlier in Korean textbooks. In 1906, Jules Bordet and Octave Gengou identified the bacterium. Scientists believe the genus may have evolved from ancestors in the soil. As humans developed agriculture, they had more contact with the soil. This allowed the ancestors of Bordetella to spread to humans. In 2003, scientists published the complete genome of B. pertussis. It consists of 4,086,186 base pairs. This is smaller than the 5.2 million base pairs in B. bronchiseptica.

Modern science shows that the bacterium is constantly changing. It was once thought to be a monomorphic pathogen. This means most strains had the same two types of alleles, ptxA1 or ptxA2. However, genome sequencing has discovered the ptxP region. Mutations in this gene have led to the ptxP3 allele. This specific strain shows increased expression of toxins. This makes the disease more acute and contagious. Since the 1990s, ptxP3 has become the dominant strain in developed countries. In 2012, epidemic outbreaks occurred in Canada, Australia, France, the UK, Japan, and the USA.

The bacteria have very specific growth requirements to thrive. They prefer an aerobic environment with a pH between 7.0 and 7.5. The optimal temperature for growth is 35 °C to 37 °C. This matches the internal temperature of the human body. They also require a nicotinamide supplement for nutrition. Their growth is hindered by fatty acids, metal ions, and sulfides. B. pertussis cannot use sugars as a carbon source. Instead, they use amino acids like glutamate for energy. They can also adapt to survive inside human macrophages and epithelial cells. They can survive in these cells for up to three days.

Understanding these biological mechanisms is vital for public health. The bacterium's ability to adapt makes it a persistent threat. It can use iron from host proteins to survive. When iron is low, it uses the Bhu system to promote heme use. This metabolic flexibility helps the bacteria endure different environments. Even in zoos, primates like chimpanzees and gorillas can catch it from humans. This shows how closely the pathogen is linked to human activity. Studying its metabolism and genome helps us develop better ways to fight it.