Bordetella Pertussis Research Paper
It is often thought that whooping cough is an outdated disease, due to the many ways we now have to combat the pathogen, but every year almost 400,000 people die due to infection with Bordetella pertussis (1, 41). Bordetella pertussis is a gram-negative coccobacillus bacterium, which causes whooping cough in humans (1, 41). The bacterium is spread by air borne particles or mucus droplets and is highly contagious. Although there is no known reservoir for the pathogen humans can often be asymptomatic, due to vaccination or immunity, and can easily spread the disease from person to person through coughing or sneezing (1, 41). Once inhaled the pathogen enters the respiratory tract and attaches to the ciliated respiratory epithelium. There
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it secretes toxins, which damage host cells and lead to serious side effects (1, 41). The disease is most common in young children or infants and although there are preventative measures that can be taken, such as the DTaP vaccine, it is still the eighth leading cause of death worldwide by an infectious agent (1, 41).
Infection with Bordetella pertussis can sometimes be hard to diagnosis and it is predicted that only 5 – 10 % on infections are recorded (1, 41). After infection with the disease there is a 5- to 10-day incubation period before the patient will exhibit any signs of the infection (1, 41). The resulting symptoms of whooping cough can vary in severity are classified into three distinct stages. The first stage is the initial catarrhal stage lasting about 1-2 weeks( 2, 1512). During this stage infected patients experience symptoms similar to that of the common cold. The second stage, termed the paroxysmal stage, is characterized by severe bouts of coughing, as many as 20 coughs in 15 second, that have a distinct whooping sound created by the sharp inhalation of air back into the lungs (2, 1512). The coughing spells at this stage can often lead to vomiting or can cause the patient to turn red or blue in the face. The final stage of the infection is termed the convalescence stage and consists of a less severe cough that can last for several months and increased susceptibility to secondary bacterial infections (2, 1512). There are preventative measures to prevent infection with Bordetella pertussis such as the DTaP vaccine, where acellular pertussis is combined with tetanus and diphtheria toxoids (1, 41). However this vaccination is a series and requires multiple vaccinations for full protection as well as booster shots of the vaccine throughout the lifespan. Infants and young children are most likely to be infected with this disease since they aren’t able to receive the vaccination series until they are at least 2 years old. For children that are too young to be vaccinated but are perceived to be at risk for developing the disease, immune serum globin can be given as a preventative measure (1, 41). Cases of whooping cough are also seen among teenagers and adults who fail to receive their booster vaccines and again become susceptible to the pathogen. Antibiotic resistance is very rarely seen with this infection, so most people diagnosed with whooping cough can be treated with Erythromycin, or another macrolide antibiotic that blocks the 70s ribosome (1, 41). However, in some cases complications can arise. Most complications are due to the severe coughing spells and include cracked ribs, abdominal hernias and in severe cases death due to lack of oxygen. Infants and young children are also at high risk of developing more serious side effects from the infection such as ear infections, pneumonia, lung collapse, brain damage, and encepatholpy (2, 1512). Infants often require hospitalization for treatment of the disease as well as supportive care (1, 41).
In order to understand why Bordetella pertussis is such a severe and effective pathogen, it is important to understand the biology surrounding the bacteria. This includes how it enters, attaches, damages, avoids natural defenses, and exits host cells. Bordetella pertussis is able to enter the body through inhalation and can then bind to the ciliated epithelium and quickly replicate on the membrane of the cell (2, 1512).
The pathogens genome encodes several proteins for the formation and secretion of virulence factors that aide in its effective attachment to these host cells such as filamentous hemagglutinin, fimbriae, and pertactin (2, 1512). Filamentous hemagglutinin is an adhesin. It has a monomeric rod like structure and consists of several beta sheet rich motifs (2, 1515). Specific amino acid sequences found in the filamentous hemmaglutinin allow the pathogen to specifically bind sulphated sugars on epithelial cells and CR3 integrins on macrophages and ciliary cells (2, 1515). Fimbriae, another virulence factor, are proteins located on the cell surface of the pathogen made up of two subunits, the major and the minor subunit (2, 1516). The minor subunit binds to monocytes at the Vla-5 subunit, and the major subunit attaches to sulphated sugars commonly found in the respiratory tract such as heparan sulphate ( 2, 1516). Although these two virulence factors have similar roles it has been shown that the filamenteous hemagglutinin plays a role in the pathogens attachment to the entire respiratory tract where as fimbriae play a more important role in attachment to laryngeal cells specifically ( 3, 1056). Pertactin is also an important virulence factor that aids in attachment of B. pertussis. It is a protein located on the outer membrane of the pathogen that has a very distinct beta helical conformation (2, 1518). The protein contains two very distinct arginine-glycine-aspartic acid sequences. These sequences are also found in proteins such as fibronectin, which mammals utilize to bind integrins (2, 1518). Therefore, this sequence allows the pathogen to specifically bind human integrins, and allows for better colonization of the
disease.
Once Bordetella pertussis has attached itself to the respiratory tract it then secretes several toxins using the Type III- secretory apparatus, which allows the pathogen to damage host cells and avoid natural host defenses (2, 1512). These toxins include the pertussis toxin, adenylate cyclase toxin, tracheal cytotoxin, and dermonecrotic toxin and all have individual functions (2, 1512). The pertussis toxin is an exotoxin secreted by the pathogen, which also remains bound to the cell during infection (2, 1516). It is composed of 5 subunits organized in a typical A-B structure. The A-B structure has been determined to have a very similar structure to other bacterial toxins such as cholera and shigella toxins (2, 1516). Each subunit plays a specific role in the virulence of the disease. The A subunit is able to insert itself through cell membrane into the cytoplasm where it exhibits ADP-ribosyltransferase activity (2,1516). This activity prevents the hydrolysis of ATP and results in the constant expression of adenylate cyclase leading to high levels of intracellular cAMP. High levels of cAMP interrupt the normal functions of the cell and leads to decreased phagocytosis and increased insulin and histamine production (2, 1516). This function is beneficial to the pathogen because it allows it to avoid being phagocytized by the cell. Adenylate cyclase toxin also affects intracellular levels of cAMP to help the cell avoid phagocytosis. It works similarly to the pertussis toxin by first utilizing its hemolytic activity to invade the host cell. However this toxin has an enzymatic function which allows it to directly stimulate the production of cAMP in the presence of Calmodulin ( 2, 1517). This causes an increase in cAMP levels close to 1000x the original concentration and has also been shown to be involved in signaling the cell suicide, apoptosis, of macrophages (2, 1518). These two toxins play an important role in infecting host cells and allowing the pathogen to survive in the host cell by evading host defenses. Another toxin produced by Bordetella pertussis is the tracheal cytotoxin. This toxin has two parts a peptide portion and a disaccharide portion (2, 1519). The disaccharide portion appears to have little impact on the toxicity but may be involved in recognition of specific binding sites on epithelial cells( 2, 1519). The C-terminal dipeptide was directly linked to the toxicity of the molecule and those molecules missing this side chain group were observed to be up to a thousand times less toxic than those expressing the unaffected side chain( 2, 1519). This toxin directly affects ciliated epithelial cells by restricting their movement and impacting the killing and removal of infected ciliary cells. It has also been shown that this toxin is linked to the release of IL-1, an interleukin, which stimulates an inflammatory response from the immune system (2, 1519). The last toxin secreted by B. pertussis is a heat stable toxin termed dermonecrotic toxin. This toxin is believed to be involved in the deamidation of RhoA, a GTP binding protein (2,1520). This inhibits GTPase activity of the Rho protein and causes it to constantly be expressed by the cell (2, 1520). Since Rho acts as a regulator to several different signaling pathways within the cell this constant expression causes incorrect signaling inside the cell, which alters the cells functioning. as a result this toxin affects cell growth and division and leads to less collagen being expressed within the cells (2, 1520). Ultimately this triggers inflammation, vasoconstriction, and dermonecrotic lesions in the areas infected with the pathogen (2, 1520)
It is also important to note that Bordetella pertussis has several ways to regulate the expression of its virulence factors. There are two mechanisms that alter the expression of these genes in Pertussis: phase variation and phenotypic modulation (2, 1512). Phase variation is the result of a frame shift mutation and leads to reversibly altered expression of the genes. This phenomenon is usually associated with the sudden loss of the ability to synthesize toxins by the bacteria (2, 1512). The other mechanism, phenotypic modulation, refers to the bacteria’s ability to change the expression of specific genes based on environmental conditions (2, 1512). For example at low temperatures, or in the presence of certain intracellular chemicals, B. pertussis represses the expression of its virulence factors (2, 1512).. Upon examination of the genome of this pathogen one locus, the bvg locus, was linked to the control of both mechanisms. The bvg locus, which contains the genes BvgA and BvgS., is responsible for the transcriptional regulation of the virulence factors. BvgS is a sensor histadine kinase, which helps detect external stimuli, and can initiate phosphorylation of BvgA, which is the response regulator (2, 1513). After phosphorylation BvgA positively regulates the virulence genes by binding to a specific target sequence and subsequently initiating transcription of the virulence factors (2, 1513).
In conclusion whooping cough is a very serious disease that caused by infection with the bacteria Bordetella pertussis. The pathogen is easily spread from person to person via airborne particles or droplets. Once inhaled the pathogen attaches to the respiratory tract where it quickly replicates and secretes toxins. These toxins have harmful impacts on the mammalian cells and lead to the symptoms of Bordetella pertussis the most common of which is the paroxysmal cough. Most cases of the disease are easily treated with macrolide antibiotics but some cases can develop serious complications, which can lead to death. Infants and young children remain the population most at risk for developing this infection since they are too young to have completed the vaccine cycle for complete protection against the pathogen. Despite the fact that we have so many preventative and combative measures against this disease it is still a very effective pathogen and remains the eighth leading cause of death by an infectious agent.
Works Cited
1. Anderson, R. P. (2006). Outbreak: cases in real-world microbiology. Washington, D.C.: ASM Press
2. Babu, M. M., Bhargavi, J., Saund, R., & Singh, S. (2001). Virulence factors of Bordetella pertussis . Current Science, 80(12), 1512-1520
3.Van den Berg, B., Beekhuizen, H., Willems, R., Mooi, F., & Furth, R. V. (1999). Role of Bordetella pertussis Virulence Factors in Adherence to Epithelial Cell Lines Derived from the Human Respiratory Tract. Infection and Immunity, 67(3), 1056-1062.
it secretes toxins, which damage host cells and lead to serious side effects (1, 41). The disease is most common in young children or infants and although there are preventative measures that can be taken, such as the DTaP vaccine, it is still the eighth leading cause of death worldwide by an infectious agent (1, 41).
Infection with Bordetella pertussis can sometimes be hard to diagnosis and it is predicted that only 5 – 10 % on infections are recorded (1, 41). After infection with the disease there is a 5- to 10-day incubation period before the patient will exhibit any signs of the infection (1, 41). The resulting symptoms of whooping cough can vary in severity are classified into three distinct stages. The first stage is the initial catarrhal stage lasting about 1-2 weeks( 2, 1512). During this stage infected patients experience symptoms similar to that of the common cold. The second stage, termed the paroxysmal stage, is characterized by severe bouts of coughing, as many as 20 coughs in 15 second, that have a distinct whooping sound created by the sharp inhalation of air back into the lungs (2, 1512). The coughing spells at this stage can often lead to vomiting or can cause the patient to turn red or blue in the face. The final stage of the infection is termed the convalescence stage and consists of a less severe cough that can last for several months and increased susceptibility to secondary bacterial infections (2, 1512). There are preventative measures to prevent infection with Bordetella pertussis such as the DTaP vaccine, where acellular pertussis is combined with tetanus and diphtheria toxoids (1, 41). However this vaccination is a series and requires multiple vaccinations for full protection as well as booster shots of the vaccine throughout the lifespan. Infants and young children are most likely to be infected with this disease since they aren’t able to receive the vaccination series until they are at least 2 years old. For children that are too young to be vaccinated but are perceived to be at risk for developing the disease, immune serum globin can be given as a preventative measure (1, 41). Cases of whooping cough are also seen among teenagers and adults who fail to receive their booster vaccines and again become susceptible to the pathogen. Antibiotic resistance is very rarely seen with this infection, so most people diagnosed with whooping cough can be treated with Erythromycin, or another macrolide antibiotic that blocks the 70s ribosome (1, 41). However, in some cases complications can arise. Most complications are due to the severe coughing spells and include cracked ribs, abdominal hernias and in severe cases death due to lack of oxygen. Infants and young children are also at high risk of developing more serious side effects from the infection such as ear infections, pneumonia, lung collapse, brain damage, and encepatholpy (2, 1512). Infants often require hospitalization for treatment of the disease as well as supportive care (1, 41).
In order to understand why Bordetella pertussis is such a severe and effective pathogen, it is important to understand the biology surrounding the bacteria. This includes how it enters, attaches, damages, avoids natural defenses, and exits host cells. Bordetella pertussis is able to enter the body through inhalation and can then bind to the ciliated epithelium and quickly replicate on the membrane of the cell (2, 1512).
The pathogens genome encodes several proteins for the formation and secretion of virulence factors that aide in its effective attachment to these host cells such as filamentous hemagglutinin, fimbriae, and pertactin (2, 1512). Filamentous hemagglutinin is an adhesin. It has a monomeric rod like structure and consists of several beta sheet rich motifs (2, 1515). Specific amino acid sequences found in the filamentous hemmaglutinin allow the pathogen to specifically bind sulphated sugars on epithelial cells and CR3 integrins on macrophages and ciliary cells (2, 1515). Fimbriae, another virulence factor, are proteins located on the cell surface of the pathogen made up of two subunits, the major and the minor subunit (2, 1516). The minor subunit binds to monocytes at the Vla-5 subunit, and the major subunit attaches to sulphated sugars commonly found in the respiratory tract such as heparan sulphate ( 2, 1516). Although these two virulence factors have similar roles it has been shown that the filamenteous hemagglutinin plays a role in the pathogens attachment to the entire respiratory tract where as fimbriae play a more important role in attachment to laryngeal cells specifically ( 3, 1056). Pertactin is also an important virulence factor that aids in attachment of B. pertussis. It is a protein located on the outer membrane of the pathogen that has a very distinct beta helical conformation (2, 1518). The protein contains two very distinct arginine-glycine-aspartic acid sequences. These sequences are also found in proteins such as fibronectin, which mammals utilize to bind integrins (2, 1518). Therefore, this sequence allows the pathogen to specifically bind human integrins, and allows for better colonization of the
disease.
Once Bordetella pertussis has attached itself to the respiratory tract it then secretes several toxins using the Type III- secretory apparatus, which allows the pathogen to damage host cells and avoid natural host defenses (2, 1512). These toxins include the pertussis toxin, adenylate cyclase toxin, tracheal cytotoxin, and dermonecrotic toxin and all have individual functions (2, 1512). The pertussis toxin is an exotoxin secreted by the pathogen, which also remains bound to the cell during infection (2, 1516). It is composed of 5 subunits organized in a typical A-B structure. The A-B structure has been determined to have a very similar structure to other bacterial toxins such as cholera and shigella toxins (2, 1516). Each subunit plays a specific role in the virulence of the disease. The A subunit is able to insert itself through cell membrane into the cytoplasm where it exhibits ADP-ribosyltransferase activity (2,1516). This activity prevents the hydrolysis of ATP and results in the constant expression of adenylate cyclase leading to high levels of intracellular cAMP. High levels of cAMP interrupt the normal functions of the cell and leads to decreased phagocytosis and increased insulin and histamine production (2, 1516). This function is beneficial to the pathogen because it allows it to avoid being phagocytized by the cell. Adenylate cyclase toxin also affects intracellular levels of cAMP to help the cell avoid phagocytosis. It works similarly to the pertussis toxin by first utilizing its hemolytic activity to invade the host cell. However this toxin has an enzymatic function which allows it to directly stimulate the production of cAMP in the presence of Calmodulin ( 2, 1517). This causes an increase in cAMP levels close to 1000x the original concentration and has also been shown to be involved in signaling the cell suicide, apoptosis, of macrophages (2, 1518). These two toxins play an important role in infecting host cells and allowing the pathogen to survive in the host cell by evading host defenses. Another toxin produced by Bordetella pertussis is the tracheal cytotoxin. This toxin has two parts a peptide portion and a disaccharide portion (2, 1519). The disaccharide portion appears to have little impact on the toxicity but may be involved in recognition of specific binding sites on epithelial cells( 2, 1519). The C-terminal dipeptide was directly linked to the toxicity of the molecule and those molecules missing this side chain group were observed to be up to a thousand times less toxic than those expressing the unaffected side chain( 2, 1519). This toxin directly affects ciliated epithelial cells by restricting their movement and impacting the killing and removal of infected ciliary cells. It has also been shown that this toxin is linked to the release of IL-1, an interleukin, which stimulates an inflammatory response from the immune system (2, 1519). The last toxin secreted by B. pertussis is a heat stable toxin termed dermonecrotic toxin. This toxin is believed to be involved in the deamidation of RhoA, a GTP binding protein (2,1520). This inhibits GTPase activity of the Rho protein and causes it to constantly be expressed by the cell (2, 1520). Since Rho acts as a regulator to several different signaling pathways within the cell this constant expression causes incorrect signaling inside the cell, which alters the cells functioning. as a result this toxin affects cell growth and division and leads to less collagen being expressed within the cells (2, 1520). Ultimately this triggers inflammation, vasoconstriction, and dermonecrotic lesions in the areas infected with the pathogen (2, 1520)
It is also important to note that Bordetella pertussis has several ways to regulate the expression of its virulence factors. There are two mechanisms that alter the expression of these genes in Pertussis: phase variation and phenotypic modulation (2, 1512). Phase variation is the result of a frame shift mutation and leads to reversibly altered expression of the genes. This phenomenon is usually associated with the sudden loss of the ability to synthesize toxins by the bacteria (2, 1512). The other mechanism, phenotypic modulation, refers to the bacteria’s ability to change the expression of specific genes based on environmental conditions (2, 1512). For example at low temperatures, or in the presence of certain intracellular chemicals, B. pertussis represses the expression of its virulence factors (2, 1512).. Upon examination of the genome of this pathogen one locus, the bvg locus, was linked to the control of both mechanisms. The bvg locus, which contains the genes BvgA and BvgS., is responsible for the transcriptional regulation of the virulence factors. BvgS is a sensor histadine kinase, which helps detect external stimuli, and can initiate phosphorylation of BvgA, which is the response regulator (2, 1513). After phosphorylation BvgA positively regulates the virulence genes by binding to a specific target sequence and subsequently initiating transcription of the virulence factors (2, 1513).
In conclusion whooping cough is a very serious disease that caused by infection with the bacteria Bordetella pertussis. The pathogen is easily spread from person to person via airborne particles or droplets. Once inhaled the pathogen attaches to the respiratory tract where it quickly replicates and secretes toxins. These toxins have harmful impacts on the mammalian cells and lead to the symptoms of Bordetella pertussis the most common of which is the paroxysmal cough. Most cases of the disease are easily treated with macrolide antibiotics but some cases can develop serious complications, which can lead to death. Infants and young children remain the population most at risk for developing this infection since they are too young to have completed the vaccine cycle for complete protection against the pathogen. Despite the fact that we have so many preventative and combative measures against this disease it is still a very effective pathogen and remains the eighth leading cause of death by an infectious agent.
Works Cited
1. Anderson, R. P. (2006). Outbreak: cases in real-world microbiology. Washington, D.C.: ASM Press
2. Babu, M. M., Bhargavi, J., Saund, R., & Singh, S. (2001). Virulence factors of Bordetella pertussis . Current Science, 80(12), 1512-1520
3.Van den Berg, B., Beekhuizen, H., Willems, R., Mooi, F., & Furth, R. V. (1999). Role of Bordetella pertussis Virulence Factors in Adherence to Epithelial Cell Lines Derived from the Human Respiratory Tract. Infection and Immunity, 67(3), 1056-1062.