Bordetella pertussis

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A Microbial Biorealm page on the genus Bordetella pertussis

Classification

Higher order taxa

Kingdom: Bacteria

Phylum: Proteobacteria

Class: Betaproteobacteria

Order: Burkholderiales

Family: Alcaligenaceae

Genus: Bordetella

Species: B. pertussis

Species

Bordetella pertussis

Other Names: “Haemophilus pertussis” (Pribram 1933) “Bacterium tussis-convulsivae” (Lehmann and Neumann 1927) "Hemophilus pertussis" (Bergey et al. 1923), and "Microbe de la coqueluche" Bordet and Gengou 1906. [10]

NCBI: Taxonomy

Description and significance

Bordetella pertussis is a small, Gram-negative, coccoid bacterium about the size of 0.8 µm by 0.4 µm. It is an encapsulated immotile aerobe that does not make spores. Bordetella pertussis produces a number of virulence factors, including pertussis toxin, adenylate cyclase toxin, filamentous hemagglutinin, and hemolysin. It cannot survive in the environment; it must reside in a host either in small groups or singly. It grows at an optimal temperature of 35-37ºC. [1]

Bordetella pertussis is a strict human pathogen that is the causative agent of pertussis (whooping cough). Its natural habitat is in the human respiratory mucosa. Whooping Cough, or pertussis, is a respiratory infection in which a “whooping” sound is produced when the sufferer breathes. Pertussis kills an estimated 300,000 children annually, most of which occur in developing countries. [6]

Genome structure

Bordetella pertussis strain Tohama I has its complete genome sequenced. The genome consists of 1 circular chromosome with 4,086,189 nucleotides (3867 genes). Approximately 67% of the genome is GC rich and its coding density is 82% (1056 bp/gene). [10]

The IncP-1 beta plasmid pBP136 from Bordetella pertussis is also sequenced. It contains 41,268 bp nucleotides and carries 46 ORFs. Two of the ORFs are similar to genes with unknown function from a plant pathogen called “Xylella fastidiosa”. pBP136 plasmid do not contain any accessory genes that code for antibiotics, mercury resistance, or xenobiotic degradation. Its role in the bacteria is unclear and is still under investigation. [9]

Cell structure and metabolism

Bordetella pertussis is an aerobe and thus uses aerobic respiration as its metabolism. Bordetella pertussis is also a Gram-negative bacterium so its cell structure consists of an outer membrane, an inner membrane and a periplasmic space with a thin peptidoglycan layer in between. On its outer membrane, Bordetella pertussis has unusual lipoopolysaccharides (LPS), endotoxins that are unlike those from other Gram-negative bacteria. It is different in that it contains two forms differing in its phosphate composition of the lipid portion of the LPS. This form is designated Lipid X, instead of the usual Lipid A form. The role of the unusual LPS is not fully understood in the pathogenesis of pertussis. [8]

Ecology

Humans are its only host. The B. pertussis bacterium resides in the upper air pathways, mostly the trachea and the bronchi. The pathogen is transmitted from person to person through droplets of respiratory secretions that are either coughed or sneezed into the air by an infected person. Without its host’s respiratory mucus, the pathogen cannot be sustained in the environment. [12]

Pathology

Humans are its only host. Pertussis is a severe, highly contagious respiratory disease characterized by outbursts of coughing followed by “whooping” sound during breathing in. Often vomiting takes place with discharge of sticky mucus. The bacteria are transmitted directly from person to person and are most contagious in its early stage of the disease. The symptoms of pertussis are similar to a common cold: runny nose, sneezing, mild cough, and low-grade fever. [1]

Bordetella pertussis has several virulence factors, one of which is the adenylate cyclase toxin (CyaA). It is the agent that causes whooping cough. CyaA invades eukaryotic cells by a calcium-dependent mechanism in which the CyaA catalytic domain is directly moved across the target cell’s plasma membrane. CyaA contains a series of a Gly-and Asp-rich nonapeptide repeats of the prototype GGXG(N/D)DX(L/I/F)X (where X can be any amino acid). This prototype is a characteristic of the repeat in toxin for the bacterial cytolysins family.[2] Another major virulence factor that is secreted by Bordetella pertussis is the pertussis toxin (PT). Pertussis toxin ADP ribosylates mammalian G(i) proteins and is a key component in the early stages of the respiratory infection. PT targets respiratory tract macrophages in promoting the infection. [5] Furthermore, like any infection, attachment to epithelial cells is a major factor in colonization. The filamentous hemagglutinin (FHA) is the virulence factor mediating adhesion to host cells. [11]

Application to Biotechnology

Bordetella pertussis has been use in medicine to develop a vaccine in order to combat the deadly childhood disease, whooping cough. The current vaccine utilizes a chemically-inactivated whole cell vaccine that has dramatically reduced the occurrence of whooping cough around the world. While side effects of the vaccine were apparent during development, they did not outweigh the risks of an epidemic. As the incidence of pertussis declined around the world and the treatment of the disease slowly diminished, people’s concern of the adverse reactions and the demand for an improved pertussis vaccine increased. Current vaccine research uses recombinant DNA technology to develop a safer approach to fight the disease. [4]

Current Research

Specificities of Antibodies:

The attachment of the microbe to the host cells is a vital step in most bacterial infection. In this research, the Bordetella pertussis’ attachment and ability to colonize in its host cells are investigated using different antibodies. Two anti-B. pertussis immunoglobulins (IgG and igA) effectively reduced attachment to host epithelial cells. This was accomplished with fimbriae-specific antibodies. Other antibodies targeting other areas were ineffective in inhibiting attachment of the bacteria to host cells, with the exception of antifilamentous hemaglutinin antibodies. However, compared to the effectiveness of fimbrae specific antibodies, the degree of antifilamentous hemaglutinin antibodies’ success of inhibiting B. pertussis’ attachment to its host cell is much smaller. [12]

Antigenic divergence of Bordetella pertussis strains:

Antigenic divergence is a major problem for vaccination because what was once an effective way to combat pathogenic microbe organisms will be no longer effective. Recent studies have suggested that such dilemma has been observed in Bordetella pertussis, the causative agent of whooping cough. The antigenic divergence between vaccine strains and circulating strains is the cause of the resurgence of pertussis incidences despite heavy vaccination. For all prevaccination strains and strains isolated in the 1960s and 1970s the ptxA2 and ptxA4 alleles were dominant. In the early 1970s, a shift in the principle allele was observed and the ptxA1 allele became common. It is still the predominant strain in the B. pertussis population. Another B. pertussis strain was also found in all prevaccination strains with the allele prn1. As with ptxA strain, a shift in the prn strain was also seen in which the proportion of prn1 allele is declining and the proportion of prn2 and prn3 alleles are rising. The antigenic divergence of predominant strains over the years had affected the effectiveness of vaccines which were developed to fight earlier pertussis strains, but are ineffective toward the latter strains. This shift in the proportion of different B. pertussis strains may explain the persistence of pertussis (whooping cough). Therefore, more effective vaccines need to be developed to combat this disease. [3]

Drug research for improved vaccine:

The current Bordetella pertussis vaccine is a whole-cell vaccine which means that the vaccine uses whole dead B. pertussis cells. The whole-cell vaccine has been very effective for the majority of the population, but some people develop severe adverse reactions to this vaccine. This acute allergic reaction to the vaccine is caused by the bacteria’s lipopolyaccharide’s endotoxic activity. Like other Gram negative bacteria, Bordetella pertussis possesses lipopolysaccharides (LPS) on its outer membrane. Normally, the lipid component of LPS, which possesses the toxicity, is anchored inside the bacteria’s own membrane. However, sometimes when the bacteria die, some of the LPS get released into the environment and thus exposing the toxic part of the LPS. Some bacteria possess LPS-modifying enzymes that can alter LPS’s endotoxic activity. These researchers investigated two such enzymes, PagP and PagL. The research suggested that the expression of PagP elevated LPS’s endotoxic activity and also endotoxic activity of the whole bacterial cells. PagL, on the other hand, decreased the endotoxic activity of LPS, but surprisingly increased endotoxic activity of the whole bacterial cells as well. This might have been a result of the increase of LPS released into the cell overall. [7]

References

1. Baron, Samuel MD, Rhonda C. Peake, and Deborah A. James et al. Medical Microbiology. Galveston (TX): University of Texas Medical Branch, 1996.

2. Bauche C, Chenal A, Knapp O, Bodenreider C, Benz R, Chaffotte A, and Ladant D. “Structural and functional characterization of an essential RTX subdomain of Bordetella pertussis adenylate cyclase toxin.” J Biol Chem. 2006. 281(25):16914-26.

3. Borisova O, Kombarova SY, Zakharova NS, van Gent M, Aleshkin VA, Mazurova I, and Mooi FR. “Antigenic divergence between Bordetella pertussis clinical isolates from Moscow, Russia, and vaccine strains.” Clin Vaccine Immunol. 2007. 14(3):234-8.

4. Burnette, W., Mar, V., Whiteley D., and T. Bartley. “Progress with a recombinant whopping cough vaccine: a review.” J R Soc Med. 1992. 85(5): 285–287.

5. Carbonetti NH, Artamonova GV, Van Rooijen N, and Ayala VI. “Pertussis toxin targets airway macrophages to promote Bordetella pertussis infection of the respiratory tract.” Infect Immun. 2007. 75(4): 1713-20.

6. Crowcroft NS and Pebody RG. “Recent developments in pertussis.” Lancet. 2006. 367(9526): 1926-36.

7. Geurtsen J, Steeqhs L, Hamstra HJ, Ten Hove J, de Haan A, Kuiperse B, Tommassen J, van der Ley P. “Expression of the lipopolysaccharide-modifying enzymes PagP and PagL modulates the endotoxic activity of Bordetella pertussis.” Infect Immun. 2006. 74(10): 5574-85.

8. Harvill, E., Preston, A, Cotter, P., Allen, A., Maskell, D., and J. Miller. “Multiple roles for Bordetella lipopolysaccharide molecules during respiratory tract infection.” Infect Immun. 2000. 68(12):6720-8.

9. Kamachi K, Sota M, Tamai Y, Naqata N, Konda T, Inoue T, Top EM, Arakawa Y. “Plasmid pBP136 from Bordetella pertussis represents an ancestral form of IncP-1beta plasmids without accessory mobile elements.” Microbiology. 2006. 152: 3477-84.

10. NCBI database entry “Bordetella pertussis” <http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=520&lvl=3&p=mapview&p=has_linkout&p=blast_url&p=genome_blast&lin=f&keep=1&srchmode=1&unlock> (retrieved on Apr 29, 2007).

11. Perez Vidakovics ML, Lamberti Y, van der Pol WL, Yantorno O, and Rodriguez ME. “Adenylate cyclase influences filamentous haemagglutinin-mediated attachment of Bordetella pertussis to epithelial alveolar cells.” FEMS Immunol Med Microbiol. 2006. 48(1):140-7.

12. Pittman, M. “The concept of pertussis as a toxin-mediated disease.” Pediatr Infect Dis. 1984. 3(5):467-86

13. Rodriques ME, Hellwiq SM, Perez Vidakovics ML, Berbers GA, and van de Winkel JG. “Bordetella pertussis attachment to respiratory epithelial cells can be impaired by fimbriae-specific antibodies.” FEMS Immunol Med Microbiol. 2006. 46(1): 39-47.

Edited by Linda Wang a student of Rachel Larsen and Kit Pogliano