Bordetella pertussis- An Overview
Bordetella pertussis is a pathogenic Gram-negative aerobic bacterium that is the causative agent of the disease pertussis or whooping cough . B. pertussis is the type species of Bordetella that consists of minute mesophilic coccobacillus that facilitates the colonization of animal tissues. B. pertussis is one of the eight species belonging to the genus Bordetella and one of the seven pathogenic species, most of which are associated with respiratory infections in humans and other animals . These are obligate pathogens of humans colonizing the ciliary epithelial cells of the respiratory tract. These are rarely present in the environment except in the form of aerosols and droplets, which is also the mode of transmission of the disease . It is an important pathogenic species of the genus Bordetella characterized by different virulence factors that enable infections. B. pertussis is a fastidious, slow-growing organism causing infections only in humans. The disease in humans is the result of excellent colonization and mesophilic growth. The infection in humans by B. pertussis is similar to infections caused by B. parapertussis in sheep as well as humans. Most Bordetella species are isolated from warm-blooded animals like humans which are mostly present in the respiratory tract of the host. However, recently these microorganisms can be isolated from other parts like human blood and human wound cultures. The bacterium was first isolated by Bergey, Harrison, Breed, Hammer, and Huntoon in 1923 and it was named Haemophilus pertussis. It was later renamed Bordetella pertussis in 1952 by Moreno-Lopez. The species name ‘pertussis’ is taken from two Latin words; ‘per’ meaning very and ‘tussis’ meaning cough, representing the severe cough caused by the bacterium. Pertussis is a severe respiratory infection that affects both the upper and lower respiratory tract of humans and is particularly severe in infants of developing countries . There have been major improvements in the reduction of pertussis by the development and improvement of vaccines over the years. However, the disease continues to be an issue in various countries with more health systems . B. pertussis is a Biosafety Level 2 pathogen that should be handled by following specific guidelines and regulations.
Bordetella pertussis is a Gram-negative, aerobic, pathogenic, encapsulated coccobacillus of the genus Bordetella, and the causative agent of pertussis or whooping cough. Pertussis is a human disease and no animal or insect source, or vector is known to exist.
B. pertussis belongs to the family Alcaligenaceae of the Betaproteobacteria, which contains several species of closely related bacteria with similar morphology. The family Alcaligenaceae is characterized by their DNA-DNA hybridization and 16S rRNA gene sequence analyses. Besides, these are differentiated by ubiquinone-8 as the major isoprenoid quinine.
The genus Bordetella consists of eight different species based on the analysis of phenotypic characteristics, DNA base composition, and nucleic acid hybridization. B. pertussis is the type species of Bordetella along with two other species B. parapertussis and B. bronchiseptica that are respiratory pathogens of mammals with an economic impact on both human health as well as agriculture. These species were even considered the subspecies of the same species which was later differentiated as different species based on the genotypic evaluation. These bacteria are grouped as B. bronchoseptica clusters as they have similar genome size and pathogenic niche.
Other members of the genus are B. avium and B. hinzii, which both cause respiratory disease in poultry and are very rarely found in humans. B. avium is also associated with respiratory infections in pigs and rabbits. B. holmesii is a human pathogen that causes septicemia, endocarditis, and respiratory infections. B. trematum is an opportunistic pathogen that causes wound infections in humans. B. petrii is an environmental isolate that has been found in soil, water, and activated sludge.
The following table summarizes the taxonomic classification of B. pertussis:
| Domain | Bacteria | | Kingdom | Proteobacteria | | Phylum | Betaproteobacteria | | Class | Burkholderiales | | Family | Alcaligenaceae | | Genus | Bordetella | | Species | Bordetella pertussis |
The following table compares some phenotypic and genotypic characteristics of B. pertussis with other Bordetella species:
|Characteristic||B. pertussis||B. parapertussis||B. bronchiseptica||B. avium||B. hinzii|
|Nitrate reduction test||Positive||Positive||Positive||Positive/Negative*||Positive/Negative*|
|Citrate utilization test||Negative||Negative||Positive||Positive/Negative*||Positive/Negative*|
|Growth on MacConkey agar||No growth||No growth||Growth||Growth/Negative*||Growth/Negative*|
|Growth on Bordet-Gengou agar||Growth with hemolysis||Growth with hemolysis||Growth without hemolysis||No growth/Growth without hemolysis*|
| Growth on Regan-Lowe agar | Growth with hemolysis | Growth with hemolysis | Growth without hemolysis | No growth/Growth without hemolysis*
| Genome size (Mb) | 4.1 | 4.8 | 5.3 | 3.7/4.1 | 3.7/4.1 | | G+C content (%) | 67.3 | 67.6 | 67.9 | 66.5/67.2 | 66.5/67.2 | | Host range | Humans | Humans, sheep | Humans, animals | Poultry, pigs, rabbits | Poultry, humans |
* Different strains may show different results.
** The medium contains cephalexin to inhibit the growth of normal flora.
The primary habitat of B. pertussis is the ciliary epithelium present in the respiratory tract of human beings . The occurrence, however, has been found in the respiratory tract of animals. It is a strict aerobic pathogen that doesn’t occur as an inhabitant of the animal body but is transmitted from other infected individuals. B. pertussis has no known reservoir other than humans, and the bacteria are assumed to transmit directly from one infected individual to another. The bacteria does, however, survive in the air forming aerosols or droplets through which it transmits from one host to the other. The ability of the bacteria to survive in the human by evading the immune system of the host and with excellent colonization characteristics. All of these attributed to the diverse and highly efficient virulence factors of the bacteria. Like most pathogenic bacteria, B. pertussis also expresses sets of gene products in response to changes in the varied environment. The long-term survival within the host and in the environment depends on the synthesis of necessary factors at different concentrations and times as a response to the directed stimuli. B. pertussis has adapted as the strict pathogen of the human body regulated by different products that act both as antimicrobial agents against other pathogens and as the virulence factors.
The morphology of Bordetella species is quite distinct from other pathogenic species which allows easier differentiation based on their morphological characteristics. The cells of B. pertussis are Gram-negative minute coccobacilli ranging in size between 0.2-0.5 µm × 0.5-2.0 µm . The cells are occasionally filamentous that can elongate several µm in length, usually observed in clinical samples.
B. pertussis is non-motile with no flagella which are used to differentiate the bacteria from other species like B. bronchiseptica and B. avium . The cells are either encapsulated or surrounded by a sheath of slime. The capsule is usually observed in freshly isolated species whereas the slime formation occurs in vitro in the form of biofilm. Both the capsule and slime sheath are composed of polysaccharides encoded by genes, but the conditions of their expression are not known.
The surface of the cell consists of fine filamentous appendages that can be observed in the form of filaments and membranous vesicles in the culture supernate . The fimbriae are 3-5 mm in width and 110-250 nm in length. These are involved in the attachment and colonization of the host cells and also act as hemagglutinogens.
As Bordetella species are Gram-negative, thus they contain an outer membrane and an inner membrane, in between which is the cell wall. The outer membrane is composed of lipopolysaccharides linked by long sugar units and anchored by lipid units. The lipopolysaccharide of B. pertussis is different from that of other Gram-negative bacteria with different phosphate composition than the lipid A in other bacteria. The lipopolysaccharide of B. pertussis acts as endotoxins that are toxic to the host and thus, acts as a virulence factor.
The cell wall is composed of a single layer of peptidoglycan consisting of glucose derivatives; N-acetyl glucosamine and N-acetylmuramic acid with pentapeptide linkages. The cell wall also contains a tracheal cytotoxin which is a disaccharide-tetrapeptide that damages the ciliated respiratory epithelial cells.
The cell membrane is a typical bacteria cell membrane with the lipid bilayer and protein particles embedded in the lipid pool. The chromosome of B. pertussis is circular with 4124236 bp and 3456 protein-coding gene sequences. The average G+C content of B. pertussis is 67.3%.
Bordetella pertussis is a fastidious and slow-growing bacterium that requires complex media and specific conditions for its isolation and cultivation. The following are some of the cultural characteristics of B. pertussis on different media and environments:
- Bordet-Gengou medium: This is a selective medium that contains potato extract, glycerol, and 20-30% blood (usually sheep or horse blood). The medium also contains antibiotics like cephalexin or polymyxin B to inhibit the growth of other respiratory flora. B. pertussis grows on this medium as small, round, convex, and shiny colonies with a mercury-like appearance. The colonies are surrounded by a narrow zone of hemolysis due to the production of dermonecrotic toxin. The colonies usually appear after 3-6 days of incubation at 35-36°C in a humid atmosphere with 5-10% CO2 .
- Charcoal blood agar (Regan-Lowe agar): This is another selective medium that contains charcoal, horse blood, and cephalexin. The charcoal absorbs fatty acids and other inhibitory substances that might interfere with the growth of B. pertussis. The colonies on this medium are similar to those on Bordet-Gengou medium, but they are more greyish and less shiny . This medium has a longer shelf-life and supports better growth of B. pertussis than Bordet-Gengou medium.
- Stainer-Scholte broth: This is a liquid medium that contains casein hydrolysate, glutamate, proline, cysteine, ascorbic acid, magnesium sulfate, iron sulfate, and nicotinamide adenine dinucleotide. This medium is used for the bulk cultivation of B. pertussis for vaccine production. The broth is inoculated with a loopful of bacteria from a solid medium and incubated at 35-36°C with shaking for 48-72 hours .
- Cyclodextrin solid medium: This is a newer medium that contains cyclodextrin, a cyclic oligosaccharide that enhances the growth of B. pertussis by binding to fatty acids and other inhibitory substances. The medium also contains yeast extract, peptone, sodium chloride, agar, and cephalexin. The colonies on this medium are similar to those on Bordet-Gengou medium but larger in size.
Bordetella pertussis is an obligate aerobe that does not grow anaerobically or microaerophilically. It does not ferment carbohydrates or produce gas from glucose. It is oxidase-positive, catalase-negative, urease-negative, nitrate-reducing, and citrate-non-utilizing . It does not require X or V factors for its growth. It shows antigenic variation and phase variation under certain culture conditions, resulting in different colony types and expression of virulence factors.
Bordetella pertussis is a gram-negative, aerobic, non-motile, encapsulated coccobacillus that belongs to the family Alcaligenaceae. It is the causative agent of pertussis or whooping cough, a respiratory infection characterized by severe coughing episodes and lymphocytosis.
Bordetella pertussis can be distinguished from other Bordetella species by its biochemical characteristics, which include the following :
- It does not ferment carbohydrates like glucose, lactose, maltose, sucrose, xylose, mannitol, gluconate, adipate, and caprate.
- It does not utilize citrate as a sole carbon source and does not produce acid from citrate.
- It does not reduce nitrate to nitrite and does not produce gas from nitrate.
- It does not hydrolyze gelatin, esculin, or urea.
- It does not produce indole or lysine decarboxylase.
- It is positive for oxidase and catalase tests.
- It is positive for chymotrypsin activity and naphthol-AS-B1 phosphohydrolase activity.
- It is positive for ester C8 lipase activity but negative for lipase C14 activity.
- It is positive for hemolysis on blood agar and produces a narrow zone of β-hemolysis around the colonies.
The biochemical characteristics of Bordetella pertussis can be summarized in the following table:
|Basic Characteristics||Properties (Bordetella pertussis)|
|Gelatin Hydrolysis||Negative (-ve)|
|Gram Staining||Gram-negative (-ve)|
|Growth in nutrient broth||Negative (-ve)|
|Nitrate Reduction||Negative (-ve)|
|Fermentation of||Properties (Bordetella pertussis)|
|Chymotrypsin activity||Positive (+ve)|
|Enzymatic Reactions||Properties (Bordetella pertussis)|
|Alkaline Phosphatase||Negative (-ve)|
|Esculin Hydrolysis||Negative (-ve)|
|Ester C8 lipase activity||Positive (+ve)|
|Lipase C14 activity||Negative (-ve)|
|Lysine decarboxylase||Negative (-ve)|
|Naphthol-AS-B1 phosphohydrolase activity||Positive (+ve)|
Bordetella pertussis is a Gram-negative bacterium that causes pertussis or whooping cough, a highly contagious respiratory disease. The bacterium produces several virulence factors that enable it to colonize the respiratory tract, evade the host immune system, and damage the host tissues. Some of the major virulence factors of B. pertussis are:
Pertussis toxin (PT): PT is a multi-subunit protein toxin that inhibits host G protein-coupled receptor signaling, causing a wide array of effects on the host. PT interferes with the chemokine receptor function of lymphocytes, impairing their migration and activation. PT also enhances the production of pro-inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), which contribute to the systemic symptoms of pertussis. PT is also involved in the induction of lymphocytosis, a hallmark of pertussis infection, by preventing the apoptosis of lymphocytes. PT is a potent adjuvant that stimulates antibody production and cellular immunity against B. pertussis antigens. PT is considered a major protective antigen and is included in acellular pertussis vaccines.
Adenylate cyclase toxin (ACT): ACT is a single polypeptide that contains an adenylate cyclase enzymatic domain coupled to a hemolysin domain. ACT targets phagocytic cells, such as macrophages and neutrophils, and inhibits their antibacterial activities. ACT binds to the alpha-M beta-2 integrin on the surface of phagocytes and translocates its adenylate cyclase domain into the cytosol. There, it catalyzes the conversion of ATP to cyclic AMP (cAMP), which disrupts the intracellular signaling pathways and impairs the phagocytosis, oxidative burst, chemotaxis, and cytokine production of phagocytes. ACT also induces apoptosis in target cells by activating caspases and mitochondrial pathways. ACT is also a hemolysin that forms pores on the membrane of erythrocytes and other cells, causing lysis and release of inflammatory mediators. ACT is an immunomodulatory toxin that elicits both protective and detrimental immune responses against B. pertussis.
Tracheal cytotoxin (TCT): TCT is a fragment of peptidoglycan released by B. pertussis during its growth. TCT damages the ciliated respiratory epithelial cells by inhibiting their regeneration and inducing their extrusion. TCT also stimulates the production of nitric oxide (NO) by epithelial cells, which contributes to the ciliostasis and tissue damage. TCT elicits an inflammatory response in host cells by activating nuclear factor-kappa B (NF-kB) and inducing the secretion of cytokines, such as IL-1, IL-6, IL-8, and TNF-alpha. TCT also activates the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, which leads to the release of IL-1 beta and IL-18, two pro-inflammatory cytokines involved in fever and inflammation.
Filamentous hemagglutinin (FHA): FHA is a cell-surface-associated protein that is secreted extracellularly into the surrounding environment. FHA plays a significant role in the initial attachment of B. pertussis to the ciliary epithelium of the respiratory tract in humans. FHA has three different binding sites and two main immune dominant regions that are highly immunogenic. FHA binds to various receptors on host cells, such as glycolipids, heparin sulfate, integrins, complement regulator factor H, and toll-like receptor 4 (TLR4). FHA mediates adherence, colonization, biofilm formation, immune evasion, and modulation by B. pertussis. FHA is also a protective antigen that induces antibody and cellular responses against B. pertussis.
Fimbriae: Fimbriae are filamentous structures that extend from the bacterial cell surface and facilitate the colonization of the respiratory tract. B. pertussis produces serologically distinct fimbriae that are composed of two major subunits, Fim2 and Fim3. The major subunits form the long filamentous structure of the fimbriae, while the minor subunit is present on the tip of the structure. The major subunits bind to glycosaminoglycans, such as chondroitin sulfate and heparin sulfate, that are present in the respiratory tract. The minor subunit enables the binding of the bacteria to cells via their cell-surface integrin VLA-5, which then significantly enhances the FHA-mediated attachment. Fimbriae are involved in the initial attachment of the bacteria to the laryngeal mucosa and are also essential for the formation of biofilm during infections.
Pertactin: Pertactin is an outer membrane protein that is also involved in bacterial adherence to the host cell surface. The mechanism employed by B. pertussis during adherence is not yet known, and no receptor involved in the process has been discovered yet. However, it is known that the amino acid sequence of the protein reveals an RGD motif, which is a known integrin-binding moiety in other bacterial adhesins, such as FHA. There have been studies that have indicated that the protein also helps in providing resistance to clearance of bacteria from the lungs. Even though the exact role of pertactin in pathogenicity is not known, it is considered an important protective immunogen that has been used in the preparation of vaccines.
Dermonecrotic toxin: Dermonecrotic toxin is a heat-labile toxin that causes necrotic skin lesions when injected subcutaneously. The toxin catalyzes the polyamination or deamidation of small Rho family GTPases, which are essential for the reorganization of the actin cytoskeleton and cell motility. The toxin has a potent vasoconstrictive activity, which can cause death or weight loss due to ischemic lesions or necrosis of the skin. The necrotizing effect of the toxin is due to the specific constrictive effect on the vascular smooth muscle. The effect on the muscle of the respiratory tract can induce a local inflammatory reaction, which accounts for some of the pathology of the disease.
Lipopolysaccharide (LPS): LPS is a component of the outer membrane of Gram-negative bacteria that acts as an endotoxin. The LPS of B. pertussis is smaller than that of other Gram-negative bacteria and is often termed lipooligosaccharide. In B. pertussis, LPS is involved in whooping cough syndrome by inducing NO production in infected tracheal cells, which results in damage to the respiratory ciliated cells. LPS also induces endotoxic activity, which may act synergistically with TCT. The NO produced destroys iron-dependent enzymes and inhibits mitochondrial function and DNA synthesis in host cells.
These virulence factors work together to enable B. pertussis to infect and cause disease in humans. Understanding their roles and mechanisms can help in developing better strategies for prevention and treatment of pertussis.
The pathogenesis of Bordetella pertussis is complex and multifactorial, involving the interaction of various virulence factors with the host immune system and respiratory epithelium. The following steps summarize the main events in the pathogenesis of B. pertussis infection :
- Entry and colonization: B. pertussis is transmitted from person to person via respiratory droplets or aerosols. The bacteria attach to the ciliated epithelial cells of the upper and lower respiratory tract, mainly by using filamentous hemagglutinin (FHA), fimbriae, and pertactin as adhesins. These factors also mediate the formation of biofilms, which protect the bacteria from clearance and enhance their persistence. The bacteria also evade the host immune system by interfering with phagocytosis, complement activation, and antibody-mediated opsonization.
- Toxin production: B. pertussis produces several toxins that damage the respiratory epithelium and modulate the host immune response. The most important toxins are pertussis toxin (PT), adenylate cyclase toxin (ACT), tracheal cytotoxin (TCT), and dermonecrotic toxin (DNT). PT is an AB5-type toxin that ADP-ribosylates G proteins, disrupting intracellular signaling pathways and causing lymphocytosis, leukocytosis, histamine sensitization, and insulin resistance. ACT is a bifunctional toxin that acts as a hemolysin and an adenylate cyclase, increasing intracellular cAMP levels and impairing phagocyte function, chemotaxis, and cytokine production. TCT is a fragment of peptidoglycan that causes ciliostasis, necrosis, and inflammation of the respiratory epithelium. DNT is a vasoconstrictor that causes local ischemia and necrosis of the skin and mucosa.
- Immune response: B. pertussis triggers both innate and adaptive immune responses in the host, but these are often ineffective or detrimental to the host. The innate immune response involves the recruitment and activation of macrophages, neutrophils, natural killer cells, and dendritic cells, which secrete pro-inflammatory cytokines such as IL-1, IL-6, TNF-alpha, IFN-gamma, and IL-17. However, these cells are also targets of B. pertussis toxins and adhesins, which impair their function and survival. The adaptive immune response involves the production of antibodies against B. pertussis antigens, mainly PT, FHA, fimbriae, and pertactin. However, these antibodies may not confer long-lasting immunity or protection against reinfection. Moreover, some studies suggest that B. pertussis may induce immunological tolerance or suppression by modulating T cell subsets and cytokine profiles.
The pathogenesis of B. pertussis results in a spectrum of clinical manifestations that vary according to age, immune status, vaccination history, and stage of infection. The disease is typically divided into three phases: catarrhal, paroxysmal, and convalescent . The catarrhal phase lasts 1 to 2 weeks and is characterized by mild respiratory symptoms such as rhinorrhea, sneezing, coughing, and low-grade fever. The paroxysmal phase lasts 2 to 6 weeks and is characterized by severe bouts of coughing followed by an inspiratory whoop sound and post-tussive vomiting. The convalescent phase lasts 1 to 12 weeks and is characterized by gradual resolution of coughing episodes and recovery of the respiratory epithelium.
Bordetella pertussis is a bacterium that causes pertussis, also known as whooping cough, a highly contagious respiratory infection that affects mainly children and infants. Pertussis can cause severe complications, such as pneumonia, seizures, brain damage, and death, especially in young and unvaccinated individuals .
The clinical manifestation of pertussis can be divided into three stages: catarrhal, paroxysmal, and convalescent .
The catarrhal stage is the initial stage of the infection, which lasts for about 1 to 2 weeks. It is characterized by mild and non-specific symptoms that resemble a common cold, such as :
- Runny or stuffed-up nose
- Low-grade fever (less than 100.4°F)
- Mild, occasional cough
- Apnea (life-threatening pauses in breathing) and cyanosis (turning blue or purple) in babies and young children
During this stage, the bacteria multiply and colonize the ciliated epithelium of the respiratory tract, producing toxins and damaging the cilia. The bacteria also evade the host immune system by inhibiting phagocytosis and complement activation. The patients are highly infectious and can spread the bacteria through respiratory droplets .
The paroxysmal stage is the most characteristic and severe stage of the infection, which lasts for about 1 to 6 weeks or longer. It is marked by episodes of violent and uncontrollable coughing that occur more frequently at night. The coughing fits are followed by a high-pitched inspiratory whoop sound, which indicates the difficulty of breathing. The patients may also experience vomiting, exhaustion, cyanosis, and weight loss due to the intensity of the coughing .
The paroxysmal stage is caused by the accumulation of mucus and debris in the airways, which trigger the cough reflex. The toxins produced by the bacteria also interfere with the normal functioning of the respiratory cells and immune cells, causing inflammation, tissue damage, and immunosuppression. The patients are still infectious during this stage, but less so than in the catarrhal stage .
The convalescent stage is the recovery stage of the infection, which lasts for about 2 to 6 weeks or longer. It is characterized by a gradual decrease in the frequency and severity of the coughing episodes, whooping, and vomiting. However, the patients may still have a non-paroxysmal cough that persists for several weeks or months. The cough may also recur with subsequent respiratory infections or irritants .
During this stage, the bacteria are gradually cleared from the respiratory tract by the host immune response and antibiotic treatment. The patients are no longer infectious at this stage. However, some patients may develop complications or sequelae due to the prolonged infection or damage to the respiratory system .
Variations in clinical presentation
The clinical presentation of pertussis may vary depending on several factors, such as age, vaccination status, previous exposure, co-infections, and host immunity .
- Infants are more likely to have severe and life-threatening symptoms, such as apnea, cyanosis, seizures, pneumonia, and death. They may not have a typical whoop or cough at all .
- Adolescents and adults are more likely to have milder and atypical symptoms, such as prolonged cough without whoop or paroxysms. They may also be asymptomatic or have a common cold-like illness .
- Vaccinated individuals are more likely to have less severe and shorter illness than unvaccinated individuals. They may also have fewer or no complications .
- Co-infected individuals may have more severe symptoms or complications due to other pathogens that affect the respiratory system.
The diagnosis of pertussis is difficult as the symptoms of the disease are similar to other mild infections like common cold or cough. The most important and useful markers that can be used as indicators of the disease are a mild increase in the leukocyte count and marked lymphocytosis. The clinical definition of the disease requires one or more typical symptoms that include inspiratory whoop and paroxysmal cough for about a week. Diagnosis of pertussis can be obtained either through the traditional method of culture and serological testing or by the use of genomic analysis to identify the organism accurately.
The samples commonly used for the diagnosis of pertussis are nasopharyngeal aspirate or nasopharyngeal swabs. The sensitivity of diagnosis depends on the technique of swab collection and secretions. The swab should be introduced deeply into the nose to reach the nasopharynx. The swabs used should be made of dacron or calcium alginate, which should then be cultured on half-strength charcoal blood agar. In the case of secretion, these should be collected with a suction device with a mucus trap. The secretions are then plated on the Charcoal agar or Bordet-Gengou medium.
Microscopic, Cultural and Biochemical characteristics
Culture is the gold standard for the diagnosis of pertussis; thus, the samples obtained from the patients are cultured on appropriate media to observe the cultural characteristics of the organism. Two distinct media can be used as the media of choice for the culture of B. pertussis, which are Bordet-Gengou and Regan-Lowe agars. To this agar, cephalexin is added to inhibit the growth of contaminating bacteria like Pseudomonas and Streptococcus. The identification of the species is made on the basis of cultural characteristics like colony morphology and culture conditions for growth. Biochemically, the bacteria can be distinguished on the basis of tests like oxidase, urease, citrate utilization, and nitrate reduction.
Direct fluorescent-antibody assay
The direct fluorescent antibody assay is usually performed directly on the samples for the microscopic visualization of fluorescent antibodies directed towards B. pertussis cells. The assay is performed on nasopharyngeal samples, but the sensitivity and specificity of the method are relatively low. The assay should be supported by other methods like culture, PCR, and serological testing.
Serological diagnosis of B. pertussis is based on the identification and variation of IgG or IgA against different virulence factors of B. pertussis during the acute and convalescent phases of the disease. The antigens often targeted during the serological testing of B. pertussis are pertussis toxin, filamentous haemagglutinin, and pertactin. The ability to produce antibodies may be affected by the disease history of immunization and disease.
Diagnosis of pertussis by PCR assays is an established method for the detection and identification of the causative agent of pertussis. PCR methods have the advantage of being more specific and sensitive than the conventional method of culture and biochemical testing. There are various primers from different chromosomal regions of the bacteria that have been developed for the diagnosis of B. pertussis. Some common issues associated with the identification of B. pertussis by PCR methods are the possibility of false-positive results and the difficulty of the process.
The treatment of pertussis can be obtained either through the use of antibiotic therapy or by vaccine immunization. The early treatment of the disease with recommended antimicrobials is useful in the prevention of harmful complications and the reduction of the duration of the disease.
The first choice for the treatment of pertussis has been the administration of oral erythromycin. The administration reduces the symptoms if used during the early course of illness. The dose of the antibiotics for children is 40-50 mg/kg given every 6 hours for 14 days.
Azithromycin is a newer antibiotic for treatment which is used 10 mg/kg on day 1 and 5 mg/kg on day 2 to 5 as a single dose. Other recommended method of treatment of B. pertussis includes antibiotics like clarithromycin and trimethoprim-sulfamethoxazole.
Even though erythromycin resistance, macrolide resistance, and fluoroquinolone resistance have been rarely found, the resistance is still rare.
The most important and efficient method of prevention pertussis is by the administration of vaccines that are either whole-cell vaccines or acellular vaccines. The first whole-cell vaccines were discovered in the 1920s, and effective vaccination started in the late 1940s.
The whole-cell pertussis vaccines are produced from the smooth forms of the bacteria, which might result in some local and systemic side effects. Due to the adverse side effects associated with whole-cell pertussis component vaccines, a new acellular vaccine has been developed.
The acellular vaccine contains purified antigens like pertussis toxin, filamentous haemagglutinin, and pertactin that are less likely to cause adverse reactions. The acellular vaccine is given as a combination with diphtheria and tetanus toxoids (DTaP) for children younger than 7 years old, and as a booster dose with reduced antigen content (Tdap) for adolescents and adults.
The recommended schedule for DTaP vaccination is at 2, 4, 6, and 15-18 months of age, and at 4-6 years of age. The Tdap booster dose is recommended at 11-12 years of age, and for pregnant women during each pregnancy.
Vaccination is the best way to prevent pertussis and its complications, especially for infants who are at high risk of severe disease and death. However, no vaccine is 100% effective, and some vaccinated people may still get infected or transmit the bacteria to others. Therefore, it is important to maintain high vaccination coverage rates among preschool children, adolescents, and adults and minimize exposures of infants and persons at high risk for pertussis.
The most effective way to prevent Bordetella pertussis infections is to get vaccinated. Vaccination can protect both individuals and communities from the disease and its complications. There are two types of vaccines available for pertussis:
- DTaP vaccine: This vaccine protects against diphtheria, tetanus, and pertussis. It is given to children in five doses, at 2, 4, 6, and 15-18 months of age, and at 4-6 years of age.
- Tdap vaccine: This vaccine is a booster dose that protects against the same diseases as DTaP, but with lower amounts of diphtheria and pertussis antigens. It is recommended for adolescents aged 11-12 years, and for adults who have not received a Tdap dose before or who are in close contact with infants or pregnant women.
Vaccination can prevent up to 95% of pertussis cases in children and 70% of cases in adults. However, the protection from vaccination can wear off over time, so it is important to get booster doses as recommended by health authorities.
Besides vaccination, other preventive measures include:
- Avoiding close contact with people who have pertussis or who are coughing or sneezing.
- Washing hands frequently with soap and water or using alcohol-based hand sanitizer.
- Covering mouth and nose with a tissue or elbow when coughing or sneezing, and disposing of used tissues properly.
- Seeking medical attention if symptoms of pertussis develop, especially in infants, pregnant women, or people with weakened immune systems.
- Taking preventive antibiotics if exposed to a person with pertussis, especially if at high risk of severe disease or complications. Preventive antibiotics can reduce the chances of getting sick or spreading the infection to others.
By following these preventive measures, pertussis infections can be reduced and controlled. Pertussis is a serious and potentially life-threatening disease that can be prevented by vaccination and good hygiene practices.
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