Fastidious Gram Negative RodsBlood Culture Unit

Division of Medical Technology

Carol Larson MSEd, MT(ASCP)

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• Fastidious– Complex / extensive nutrient requirements

• Faint staining Gram Negative Rods– Safranin counterstain for >2 minutes– Substitute carbolfuschin for safranin

• Serological testing useful

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General Information

Brucella species

Clinical 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

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• Blood, bone marrow or tissue

• Risk of lab acquired infection

• Specify on requisition when suspecting Brucella

• BAP, CHOC, BCYE, Blood Culture broth

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Brucella species

Specimen Collection

• 35C, 5-10% CO2 for 21 days

• Colony morphology– Growth at 7 days– BAP = smooth

glistening, translucent colonies that become brown with age

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Brucella species

Growth Characteristics

• Gram stain: tiny, faint staining gram negative coccobacilli

• Oxidase +, Catalase +

• Nitrate +

• Glucose oxidizer

• Nonmotile

• Additional tests to speciate

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Brucella species

Identification

• Tube agglutination test– Single titer of >=1:160– Fourfold rise in titer between acute and

convalescent specimens

• Does not detect Brucella canis

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Brucella species

Serological Testing

• Doxycycline and rifampin for 6 weeks

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Brucella species

Treatment and Prevention

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.

• 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

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Eikenella corrodens

Clinical Significance

Eikenella corrodens

Specimen Collection• Aerobic

• Requires hemin

• BAP, CHOC

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• Tiny colonies at 48 hrs

• Colony morphology– BAP

• “Pits" the agar• Pale yellow pigment• Greening around colony• Bleach odor

– MAC – no growth

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Eikenella corrodens

Growth Characteristics

Eikenella corrodens

Identification• Small, slender Gram Negative Bacilli

• Oxidase +

• Catalase –

• Glucose non-oxidizer (asaccharolytic)

• Nitrate +

• Nonmotile

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• Susceptibility testing not routinely done

• Treat with:– Penicillins– 3rd generation cephalosporins– Tetracycline– Quinolones

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Eikenella corrodens

Treatment and Prevention

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.

• Haemophilus aphrophilus

• Actinobacillus actinomycetemcomitans

• Cardiobacterium hominis

• Eikenella corrodens

• Kingella kingae

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HACEK Group

Organisms

• Subacute bacterial endocarditis

• Blood Cultures

• Subculture to various enriched media and hold for extended time beyond 1 week– BCYE

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HACEK Group

Clinical Significance

What organisms are included in the HACEK group?

Haemophilus aphrophilusActinobacillus actinomycetemcomitansCardiobacterium hominisEikenella corrodensKingella kingae

• Looked at several organisms

• Clinical significance

• Specimen collection, transport & processing

• Growth characteristics & identification

• Serological testing

• Treatment and prevention

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Fastidious GNR

Summary

Who am I?

BAP, growth appears at 7 days Gram Stain

Brucella species

Causes Undulant Fever