Pseudomonadaceae

Pseudomonas, Aeromonas and Burkholderia species

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Pseudomonas and Burkholderia

• Gram negative rods• Obligate aerobes• Oxidise carbohydrates (not fermentative)• Oxidase, catalase positive• Motile by one or more flagellae (B. mallei non-motile)• Grow well on Maconkey agar• P. aeruginosa produces diffusible pigments

(pyocyanin, pyoverdin)• P. aeruginosa is an opportunist pathogen• B. mallei causes glanders, B. pseudomallei causes

melioidosis

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Habitat

• Pseudomonads are environmental organisms occurring worldwide in water, soil and vegetation

• P. aeruginosa may be also found on skin, mucous membranes and in faeces

• B. pseudomallei lives in soil where it may infect man and animals. Widely distributed in tropical and subtropical regions of southeast Asia and Australia

• B. mallei may survive in the environment for up to 6 weeks but its reservoir is infected Equidae.

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P. aeruginosa infections

• Causes a wide range of opportunistic infections• Predisposing factors associated with many of these

infections – defective or altered normal host defences• Bovine mastitis linked to contaminated water for

udder washing or insertion of intra-mammary antibiotics

• Fleece rot of sheep (associated with prolonged rainfall). Maceration of skin followed by water penetration of the fleece allows colonisation resulting in suppurative dermatitis. Pyocyanin pigment produced by P. aeruginosa discolours the wool

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Diagnosis• Specimens for lab diagnosis include pus (green pus

sometimes), respiratory aspirates, mastitic milk, etc• Blood agar and MacConkey inoculated and incubated

at 37 degrees for 24-48 hours.• Colonies are large, greyish-blue• Identified by colonial morphology and characteristic

fruity odour (grape-like).• Pyocyanin production. Enhanced when grow on P.

agar (also called DIFCO).• Non lactose fermenter on Maconkey agar• Oxidase positive• Shows multiple resistance to antibiotics• API 20E

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MacConkey

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Virulence factors of P. aeruginosa – survival in diverse environments and large number of virulence factors

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Treatment

• Predisposing causes and sources of infection identified and eliminated

• P. aeruginosa very resistant to many antibiotics so lab susceptibility testing needs to be performed on isolates (aminoglycoside + anti-pseudomonal beta lactam usually effective)

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Glanders

• Caused by Burkholderia mallei, Gram negative rod - • Rare - once worldwide but now in Middle East, India,

Pakistan, China, Mongolia• Contagious disease of Equidae characterised by

formation of nodules and ulcers in the respiratory tract and skin

• Humans and carnivores also susceptible to infection – potential bioterrorism agent

• Transmission by ingestion of food or water contaminated by nasal discharges of infected horses, also by inhalation or skin abrasions

• Over 200 000 horses were destroyed because of glanders during the First World War

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Clinical features• Acute septicaemia with fever,

mucopurulent nasal discharge and respiratory signs

• Chronic disease more common presenting as nasal, pulmonary and cutaneous forms

• Ulcerative nodules develop on the mucosa of the nasal turbinates and nasal septum

• Purulent nasal discharge and regional lymphadenopathy present

• Cutaneous form (Farcy) is a lymphangitis in which nodules occur along the lymphatic vessels of the limbs. Ulcers develop and discharge pus.

• Animals may die after months or recover and shed organisms from RT or skin

• Pathogenesis not well defined – organism dangerous to work with!

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exposed nasal septum of a horse showing the range of lesions observed in glanders

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Diagnosis

• Clinical signs• Lab diagnosis by sending pus, lesion discharge,

blood for serology • (warn the lab-category 3 organism)• B. mallei will grow on simple media but not

MacConkey.• Colonies are smooth, white, 1-2 mm.• Serology; e.g. complement fixation, agglutination• Mallein test

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Mallein test

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Treatment and control

• Test and cull

• Antibiotics are inappropriate as treated animals may carry the organism and transmit it

• Cleaning and disinfection of contaminated areas (formalin or iodophor)

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Melioidosis

• Caused by Burkholderia pseudomallei• Endemic in soil and water in south east Asia (‘Vietnam

time-bomb’), tropical Australia (Darwin)• Infection results from ingestion, inhalation or skin

abrasion from soil/water contact• Opportunistic pathogen, stress-immunosupression

predisposes to clinical disease

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Melioidosis

• Many animal species, including man, susceptible, subclinical infections occur in which the organism may remain latent and then re-activate

• Infection may be acute or chronic, septicaemic, respiratory, disseminated and characterised by abscess formation

• Organism may be cultured on blood agar or Ashdowns medium

• Colonies are shiny, yellowish brown, small or rough with wrinkled corrugated surface

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L’affaire du Jardin des Plantes• Horse from menagerie (zoo!) at Jardin des Plantes discovered

by chance by a visitor from the Institute Pasteur in Paris to have melioidosis

• Numerous other animals at the Jardin had melioidosis and soil contaminated with the organism

• Zoo closed to help stop outbreak• Disinfection of environment and slaughter of all animals followed• To late – 2 other zoos affected and dissemination of B.

pseudomallei across France discovered• Horses bore the brunt of infection, cases among animal

handlers – 2 human deaths• Epidemic subsided – healthy respect among vets for B.

pseudomallei in France ever since!• Infection imported by horses from Iran or giant panda from

China!??

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AEROMONAS

• Gram negative rods (3-4 μm)• Grow at room temperature (25°C)• Non lactose fermenting• Ferment glucose – often with gas

production• Motile (except A. salmonicida)• Primarily pathogens of reptiles and fish

although some can infect mammals and birds

• A. hydrophila - haemolytic, Enteritis, Food poisoning in man

• A. salmonicida –Brown pigment, Furunculosis in salmonids.

• Isolation of A. salmonicida on blood agar at (25°C) for 48h

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PIGMENT IN A. salmonicida (L) A. hydrophila (R)

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FURUNCULOSIS

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Vibrio

• Curved Gram negative rods (3-4 μm)• Catalase positive• Ferment glucose • Motile• Require NaCl for growth• Significant in medical rather than vet microbiology• Main spp. are V.cholerae (the Cholera bacillus) and

V.parahaemolyticus (food poisoning)• Only V.metschnikovii is associated with disease in

animals. It causes cholera-like symptoms in chickens

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