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Fastidious Gram Negative Rods Blood Culture Unit

Explore Brucella & Eikenella: clinical significance, specimen collection, growth characteristics & identification, serological testing, treatment & prevention. Details on HACEK group organisms and key identifying characteristics.

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Fastidious Gram Negative Rods Blood Culture Unit

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  1. Please click audio icon to hear Carol’s narration Fastidious Gram Negative RodsBlood Culture Unit Division of Medical Technology Carol Larson MSEd, MT(ASCP)

  2. Click icon for audio General Information • Fastidious • Complex / extensive nutrient requirements • Faint staining Gram Negative Rods • Safranin counterstain for >2 minutes • Substitute carbolfuschin for safranin • Serological testing useful

  3. Click icon for audio Brucella speciesClinical Significance • Causes Brucellosis / Undulant fever / Malta fever • Transmission via: • Direct contact with infected animals • Ingestion of contaminated meat or dairy products • Inhalation of the aerosolized organism • Facultative intracellular organism

  4. Click icon for audio Brucella speciesSpecimen Collection • Blood, bone marrow or tissue • Risk of lab acquired infection • Specify on requisition when suspecting Brucella • BAP, CHOC, BCYE, Blood Culture broth

  5. Click icon for audio Brucella speciesGrowth Characteristics • 35C, 5-10% CO2 for 21 days • Colony morphology • Growth at 7 days • BAP = smooth glistening, translucent colonies that become brown with age

  6. Click icon for audio Brucella speciesIdentification • Gram stain: tiny, faint staining gram negative coccobacilli • Oxidase +, Catalase + • Nitrate + • Glucose oxidizer • Nonmotile • Additional tests to speciate

  7. Click icon for audio Brucella speciesSerological Testing • Tube agglutination test • Single titer of >=1:160 • Fourfold rise in titer between acute and convalescent specimens • Does not detect Brucella canis

  8. Click icon for audio Brucella speciesTreatment and Prevention • Doxycycline and rifampin for 6 weeks

  9. How long must cultures be held when Brucella is suspected? Culture plates and media must be held for at least 21 days because Brucella is a slow grower.

  10. Click icon for audio Eikenella corrodensClinical Significance • Normal flora of mouth, respiratory & GI tracts • Opportunistic pathogen • Associated with: • Dental / periodontal and head / neck infections / abscesses • Human bite wounds • Septicemia following tooth extraction • Endocarditis

  11. Click icon for audio Eikenella corrodensSpecimen Collection • Aerobic • Requires hemin • BAP, CHOC

  12. Click icon for audio Eikenella corrodensGrowth Characteristics • Tiny colonies at 48 hrs • Colony morphology • BAP • “Pits" the agar • Pale yellow pigment • Greening around colony • Bleach odor • MAC – no growth

  13. Click icon for audio Eikenella corrodensIdentification • Small, slender Gram Negative Bacilli • Oxidase + • Catalase – • Glucose non-oxidizer (asaccharolytic) • Nitrate + • Nonmotile

  14. Click icon for audio Eikenella corrodensTreatment and Prevention • Susceptibility testing not routinely done • Treat with: • Penicillins • 3rd generation cephalosporins • Tetracycline • Quinolones

  15. What are the key identifying characteristics for Eikenella corrodens? It pits the agar and has a bleach smell on BAP at 48 hours, it will not grow on MAC, it is oxidase positive, catalase negative, glucose N“F”/N“O”, and nitrate positive.

  16. Click icon for audio HACEK GroupOrganisms • Haemophilus aphrophilus • Actinobacillus actinomycetemcomitans • Cardiobacterium hominis • Eikenella corrodens • Kingella kingae

  17. Click icon for audio HACEK GroupClinical Significance • Subacute bacterial endocarditis • Blood Cultures • Subculture to various enriched media and hold for extended time beyond 1 week • BCYE

  18. What organisms are included in the HACEK group? Haemophilus aphrophilus Actinobacillus actinomycetemcomitans Cardiobacterium hominis Eikenella corrodens Kingella kingae

  19. Click icon for audio Fastidious GNRSummary • Looked at several organisms • Clinical significance • Specimen collection, transport & processing • Growth characteristics & identification • Serological testing • Treatment and prevention

  20. Who am I? BAP, growth appears at 7 days Gram Stain Causes Undulant Fever Brucella species

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