Bordetella

Genus Bordetella

Genus Bordetella
Includes the following species: B. pertussis B. parapertussis B. bronchiseptica

General characteristics

Small gram negative coccobacilli . Some species are motile .

General characteristics

All are catalase +B. pertussis and B. bronchiseptica are oxidase +ve , while B. parapertussis is oxidase –ve.Require nutritional elements including nicotinamide, organic sulfur (cysteine) and organic nitrogen ( aminoacids).

Cont,

B. pertussis is the most fastidious among this genus and does not grow on simple medium.B. pertussis grows slowly , it is susceptible to cold and desiccation .Without its host’s respiratory mucus tissue, the pathogen cannot be sustained in the environment.

Epidemiology

Humans are the only host for B. pertussis and B. parapertussis . Pertussis is transmitted from person to person by resp . droplets. Most of the patients with pertussis are less than a year old although older children may also get the disease.

Epidemiology

B. pertussis is isolated in recent years from patients with HIV infection B. bronchiseptica is found in a variety of animal spp. (rabbits , dogs , cats ,swine , foxes ) and occasionally in man


Pathogenesis
Bordetella produce a number of toxins and virulence factors : PT (pertussin toxin) : it is protein consist of six subunits ( A/B subunits).

Pathogenesis

This toxin has the following effects :1. Histamine- like effect. 2. production of T- lymphocytosis due to decrease entry of lymphocytes into lymph nodes. 3.It inhibits an intracellular protein that regulates the change of ATP to cAMP, the end result is the accumulation of large amount cAMP which interfere with the function of cells including phagocytes. 4. It inhibits many leukocyte functions, including chemotaxis, phagocytosis and respiratory burst and impairs NK cell killing.

Cont,

Adenylate cyclase toxin ( ACT ) , this exotoxin penetrates the host cells, like PT, it also inhibits phagocyte and NK cell functions. Tracheal cytotoxin ( TC ) , it causes ciliostasis , inhibition of DNA synthesis causing cell death. The toxin is a fragment of cell wall peptidoglycan

Pathogenesis

Dermonecrotic toxin, is a very strong vaso-constrictor and causes ischemia and extravasation of leukocytes and, in association with tracheal cytotoxin, causes necrosis of the tracheal tissue.

Cont,

LPS endotoxin, like LPS of other gram negative bacteria, these endotoxins cause a number of patho-physiolocigal effect. They activate a variety of inflammatory mediators ( TNF, IL-1, IL-6, prostaglandins) and also activate complement system.

Cont,

Filamentous hemagglutination ( FHA) , (agglutinogens), these are not exotoxins but are filament-associated lipo-oligo-saccharides which are implicated in the binding of the organism to ciliated epithelial cells. Antibodies against these molecules are protective, probably by preventing bacterial attachment.

Clinical picture

Is disease of children and can be divided into 3 stages :1st stage : Catarrhal stage , mild cough with flu like illness with runny nose , last for 1-2 wks. 2nd stage ,Paroxysmal stage :episodes of severe and violent cough increase in number as many as 15 – 25 cough episodes occur per day and is associated with vomiting and whooping as air is rapidly inspired into the lungs past the swollen glottis.There is no time for breathing between coughs and the paroxysm may be sufficient to induce anoxia.


Cont,
Hypoxia during prolonged attacks may lead to seizure, hypoxic encephalopathy or coma. No fever , no sign of systemic illness , this stage lasts from 1- 4 weeks 3rd stage :Convalescent stage, symptoms slowly decrease, can last as long as 6 months after infection .

Clinical picture

B. parapertussis
Produces similar disease to whooping cough, usually subclinical or in the form of non-specific bronchitis.

B. bronchiseptica

Causes kennel cough in dogs & atrophic rhinitis in swine. It is rarely found in humans in whom it causes pertussis- like symptoms in immunocompromised patients

Lab diagnosis

Clinical specimens are nasopharyngeal aspirate or nasopharyngeal swab. A fluid transport medium may be used for swabs but must be held for less than 24hr.

Lab diagnosis

Lab diagnosis


Cultivation
Selective medium for isolation of B. pertussis & B. parapertussis is Bordet-Gengo , it is potato infusion agar with glycerol & sheep blood. Plates are incubated at 35ᴼC in a humidified atmosphere without elevated CO2 for up to 12 days, most isolates are detected within 3-5 days. Young colonies of B.pertussis are small , rounded & shiny resembling mercury drops.Not require X or V factors .

Culture

Antimicrobial therapy
Erythromycin is the drug of choice Cotrimoxazole is an alternative drug.

Prevention