Bordetella pertussis in Canada

Introduction

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Description of the microbe

The bacterium Bordetella Pertussis is the causative agent of Whooping Cough. This small bacterium (about .8um in length and .4um by width) cannot survive in the open environment, and therefore must reside in a host, and is considered pathogenic. This host is almost always a human, where its “natural” environment is said to be the mucus in the human respiratory tract. The optimum temperature of growth for B.pertussis is about 35-37C, which is the temperature inside a living human host.

B.pertussis is an aerobic gram negative bacterium that does not produce spores. Due to its lack of flagella, it is also immotile. It resides in the phylum Proteobacteria, class Betaproteobacteria, order Burkholderiales, and family Alcaligenaceae. Because it is an aerobe, it utilizes aerobic respiration. Therefore, the bacterium consists of an electron transport chain on its membrane, and is considered a chemoheterotroph. Like other gram negative bacteria, it possesses an inner and outer membrane, with a thin peptidoglycan cell wall in between. This cell wall is attached to the outer membrane via lipoproteins. Like other gram negatives, the outer membrane of B.pertussis is coated with LPS (lipopolysachharides), which are long sugar linked and lipid-anchored polysaccharides coating the outer membrane. LPS are endotoxins, meaning that they are toxic to host (or potentially other bacteria) cells when detached from the bacteria. However, B.pertussis consists of very unusual LPS compared to other gram negatives. Namely, it contains two forms of LPS that have a different phosphate composition than standard Lipid A form LPS.

Bordetella pertussis does not necessarily cause whooping cough by itself, but rather produces toxins that do so. Among producing pertussis toxin, filamentous hemagglutinin, and hemolysin, B.pertussis produces the adenylate cyclase toxin (CyaA) – a direct causative agent of Whooping Cough. CyaA invades eukaryotic cells by a calcium-dependent mechanism in which the CyaA catalytic domain is directly moved across the target cells plasma membrane. CyaA has a series of G and D rich polypeptide residues, which is a characteristic repeat for similar toxins. B.pertussis attaches to host cells via the virulence factor P.69 pertactin, which is an extracellularly exposed domain of a membrane protein expressed by B.pertussis – and targets the adhesion to mammalian cells. It consists of an RGD tripeptide motif which attaches to various sites on mammalian adhesion proteins (some include fibronectin, vitronectin, and fibrinogen). In addition to this, the filamentous hemagglutinin (FHA) also helps mediate cell adhesion, and contains similar motifs as P.69 pertactin. Once attached, B.pertussis is able to transfer CyaA to the target host cell.

The pertussis toxin (PT), also produced by B.pertussis, is known to also be an important factor in whooping cough respiratory infections. PT catalyzes ADP-ribosylation of the alpha subunit of G(i) proteins, preventing the exchange of GDP-GTP, thus blocking the inhibition of adenylyl cyclase by G(i). This will destroy the ciliated epithelial cells that normally would sweep away mucus, and without this ciliated action, vigorous coughing is needed to clear the tract. This coughing is painful, and also is what spreads the highly contagious B.pertussis to others.

The Tahoma 1 strain of B.pertussis has its entire genome sequenced – it is 1 circular chromosome 4,086,189 nucleotides long (3867 genes), of which about 67% of the entire genome is GC rich.

Link to MicrobeWiki Page: Bordetella pertussis http://microbewiki.kenyon.edu/index.php/Bordetella_pertussis

Description of the disease

Bortadella Pertussis secretes numerous toxins known to affect cellular homeostasis. The primary disease caused by the microbe is known as “Pertussis” (commonly referred to as 'Whooping Cough').

General Disease Information:

Whooping cough is characterized by uncontrollable, heavy coughing fits which persist for many weeks. Initially the symptoms may mimic that of the common cold, later developing into severe coughing and the potential development of further illness i.e. pneumonia, hypoxia (oxygen deprivation to tissues), apnea (suspension of breathing), seizures, etc. The disease progression can be broken up into several stages, each characterized by different symptoms. Initially the patient enters the “Catarrhal Phase” in which they display symptoms like that of the common cold. This usually develops within the first two weeks of disease. The second major stage is referred to as the “Paroxysmal Stage” and is characterized by uncontrollable fits of coughing followed by high pitched ‘whoop’ sounds upon air uptake. This stage is the most severe and is often the time when a patient will exhibit other disease symptoms. If the patient has the immune strength to combat the illness, they enter the final stage called the “Convalescent Stage”. Here the patient begins recovery from disease and uncontrollable coughing slowly diminishes.

Molecular Mechanisms of Disease:

Pertussis can act through numerous virulent mechanisms to affect the host organism. Two of the more notable toxins secreted by Bortadella pertussis are Pertussis Toxin (PT) and Adenylyl Cyclase Toxin (CyaA).

Pertussis Toxin (PT)

Pertussis toxin directs its activity intracellularly by affecting the inhibitory subunit of G-protein coupled receptors. PT catalyzes the ADP-Ribosylation of the Gi subunit and prevents inhibition of the protein Adenylyl Cyclase (AC). Adeneylyl Cyclase is responsible for the production of intracellular cAMP, a common downstream messenger in many cell signaling pathways.

In a normal cell, Gi subunits work concurrently with Gs proteins. Gs proteins are responsible for the activation of AC while Gi is responsible for inhibiting AC. When functioning properly, the two proteins regulate intracellular cAMP levels to maintain cellular homeostasis. In a cell affected by PT, Gi is inhibited and cannot act to “shut off” AC. As a result, the AC is not regulated and will constitutively produce cAMP until the Gs protein is removed. These high levels of cAMP have extreme downstream effects on gene expression and the viability of the cell. This destroys the ciliated epithelial cells that normally would sweep away mucus, and without this ciliated action, vigorous coughing is needed to clear the airway.

Adenylyl Cyclase Toxin (CyaA)

CyaA is the primary toxin that contributes the development of 'Whooping cough' symptoms. It predominantly controls the initial localization of microbe to the lung and airway tissues for colonization. B. pertussis adheres to the host cell via P.69 pertactin virulence factor. This extracellular domain facilitates interaction between the mammalian host cell and the bacterial microbe. CyaA acts on cells in both calcium and temperature-dependent manners where the CyaA catalytic domain is directly moved across the target cells plasma membrane. Specifically, it binds and invades cells by forming transmembrane cation selective channels. These channels can further affect the affected cell by offsetting cellular homeostasis, occasionally resulting in cellular lysis. CyaA may also contribute to the increase in intracellular cAMP levels of the host cell.

Transmission of disease

Bordetella pertussis cannot live in the outside environment. As a result, it has evolved to become a highly contagious microbe which is most commonly spread airborne. B. pertussis has negative effects on the airway tissues resulting in the loss of cilia mucus sweeping functions. The affected individual must now cough rigorously to clear the airway of excess mucus. The strong, uncontrollable coughing provides a mechanism for B. pertussis to leave the internal host environment and infect other individuals.

Why is this disease a problem in Canada

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What is being done to address this problem

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What else could be done to address this problem

Are there solutions that could be successful but haven't been implemented due to political or economic reasons? Are there successful efforts in other countries? Are there reasons why these efforts may or may not be successful in the country you've focused on? etc. etc.

References

Char, Ian; Chatfield, Steven; Douce, Gillian; Everest, Paul; Li, Jingli; “Role of the Bordetella pertussis P.69lpertactin protein and the P.69/pertactin RGD motif in the adherence to and invasion of mammalian cells”; http://mic.sgmjournals.org/cgi/reprint/142/11/326.

Cox, Michael M.; Nelson, David L.; Principles of Biochemistry. W.H. Freeman and Company, New York, NY.

Edited by Bryan Dieffenbach, Gorjan Hrustanovic, Patricia Lee and Andrew Chen, students of Rachel Larsen