Celine - Gram Negative Rods - Pasteurella, Bordetella, Brucella Flashcards
Write about Pasteurella
(6)
Colonise mammals both domestic and feral
Normal nasopharyngeal flora for cats and dogs
Most human disease associated with some form of animal contact most commonly dog bites or cat scratches - zoonosis
Six species
P. multocida most commonly infects humans
Isolated from 50% of dog bites and 75% cat scratches
What three syndromes are associated with Pasteurella
Skin and soft tissue infections localised swelling and cellulitis following dog bite/cat scratch
Chronic pulmonary disease in lung dysfunction patients
Systemic infection in immunocompromised host
What virulence factors are associated with Pasteurella
Capsule
Endotoxin
What does diagnosis of pasteurella depend on
Clinical appearance
History of animal contact
Results of culture
What clinical specimen is seen in Pasteurella
Usually pus from skin/tissue infection
Write about the isolation of Pasteurella
(3)
Not fastidious
Grows on blood agar, incubated at 37 degrees in air over night
But fails to grow on MacConkey - good clue
Write about the colonial morphology of Pasteurella
(4)
1 mm white/grey wet colonies
Gram-negative coccobacilli old cultures bipolar ‘safety pin’ staining
Oxidase positive
Catalase positive
What confirmatory tests are carried out for P. multocida
Biochemical tests
- Fermentation - peptone water ‘sugars’ - glucose, maltose, sucrose
Indole production
Ornithine decarboxylase test
Write about the fermentation of peptone waters for Pasteurella
Fermentates glucose and sucrose
i.e. yellow colour after addition of Phenol Red indicator
Write about indole production by Pasteurella
(5)
Peptone media is a source of the amino acid trytophan
Hydrolysis of trytophan, leads to accumulation of indole
Add Kovacs reagent
Cherry red colour on surface is positive
Red colour seen in pasteurella
Write about Ornithine decarboxylase test for Pasteurella
Decarboxylase broth contains nutrients, dextrose, pH indicator (purple) plus a single amino acid e.g. ornithine, lysine
Carboxylase breaks down ornithine - alkaline by-products-pH drop-indicator- purple colour change
Control tube - only dextrose ferments dextrose - pH decrease = yellow colour
P.multicoda positive for ornithine decarboxylase
Write about Bordetella
(4)
Gram negative, small rod/ovoid pairs
Boretella pertussis
Bordetella parapertussis
Bordetella bronchiseptica
Write about Bordetella pertussis
Exclusively human pathogen
Infects ciliated bronchial epithelial cells
Induces excess mucous secretion -> whooping cough
Highly contagious disease
Significant morbidity and mortality worlwide where vaccination unavailable
Worldwide deaths > 300,000/ year
In Ireland pertussis vaccine offered to all children as part of the routine immunisation programme since 1952
In absence of active immunisation -> disease dangerous in young child
Write about Pertussis epidemiology
(5)
Over time significant decrease in infection since vaccine introduction in 1952
Marked increase in pertussis since 2011/2012 predominantly affecting infants incidence highest children < 1 year
Similar increase in other countries - waning immunity in mothers contributory factor
Booster introduced in 2012 for health care workers and pregnant women
Cases begining to decrease again
Write about whooping cough
(4)
3 phases: Catarrhal, paroxysmal, convalescence
CNS dysfunction in around 10% cases
Infection not as dangerous in older children and adults
Adolescents/adults reservoir for infection for young children
What is catarrhal whooping cough
Nonspecific symptoms - malaise mild fever, highly contagious
What is paroxysmal whooping cough
Bouts of coughing followed by “whoop”
What is convalescent whooping cough
Complications may include pneumoniae and encephalitis
What are the virulence factors for B. pertussis
Fimbriae
Haemagglutinin
Lipooligosaccharide
Toxins
What toxins are produced by B. pertussis
(4)
Pertussis toxin - lymphocytosis
Dermonecrotic toxin - tissue necrosis
Tracheal cytotoxin - inhibits cilia movement
Adenyl cyclase toxin - decreases phagocytosis
What do fimbriae do for B. pertussis
Bind ciliated epithelium in URT
What does haemagglutinin do in B. pertussis
Attachment to epithelium
What does lipooligosaccharide do in B. pertussis
Immune evasion
What are the toxins in Bordetella pertussis
Pertussis toxin
Dermonecrotic toxin
Filamentous haemagglutinin
Tracheal cytotoxin
Adenyl cyclase toxin
Fimbriae
What is pertusis toxin
Lymphocytosis, sensitisation to histamine, activation of insulin production resulting in hypoglycaemia
What does dermonecrotic toxin do
Causes vasoconstriction and ischemic necrosis
What does filamentous haemagglutinin do
Facilitates attachment of bacteria to ciliated epithelial cells
What does adenyl cyclase toxin do
Decreases chemotaxis and phagocytosis of bacteria
What does tracheal cytotoxin do
Inhibits cillia movement and regeneration of damaged cells
What does fimbriae
Promotes attachment of bacteria to host cells
Write about the B. pertussis specimens
Its very fastidious pathogen so specimen collection and transport is important
Nasopharyngeal swab (both nostrils) or cough plates
Transport - charcoal transport swab
Write about the Day 1 isolation of B. pertussis
Bordet-Gengou (BG) agar
Incubate at 37 degrees for 3-7 days
What is Bordet-Gengou (BG) agar - 30%
(3)
Sheep blood in potato glycerol agar
+/- antibiotics
Made fresh to order
Write about the colonial morphology of B. pertussis
Smooth, raised, glistening ‘mercury drops’
Gram-neg rods/cocci
Oxidase positive
Catalase positve
What day 2 confirmatory tests are used for B. pertussis
(3)
Citrate utilisation
Antigen detection
Molecular testing
Write about citrate utilisation in B. pertussis
Citrate slope (green) - sole carbon source
Utilise citrate -> pH increased - blue colour
B. pertussis = citrate positive
Write about antigen detection for B. pertussis
Direct fluorescent antibody test-nasopharyngeal smear
Write about molecular testing for B. pertussis
PCR increasingly used for direct detection in specimen due to fastidious un-reactive nature of pathogen
CHI - Crumlin
