Eikonella corrodens - MegaMicro

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Eikonella corrodens

Microbiology > Bacteriology > Gram-negative bacteria > Gram-negative bacilli > HACEK organisms
• Fastidious, facultative anaerobic, Gram negative rod (often coccobacillary), oxidase positive and non-motile.  
• The genus Eikenella contains only one species and is a member of the family Neisseriaceae.  Also a member of the AACEK (formerly HACEK) group of organisms that requires an atmosphere enhanced with CO2 for growth.

• Named after Eiken who characterized this organism and observed its ability to pit or “corrode” the agar.
• Reservoir:  endogenous flora of the mouth and upper respiratory tract; mucosal surfaces of the genitourinary and gastrointestinal tracts.
• Many patients with Eikenella infections have underlying diseases, especially head and neck malignancies.

• Virulence factors:  limited data available, but the organism does have adherence pili (mucosal cell adhesion) and an extracellular polysaccharide “slime layer” (inhibition of phagocytosis).

Disease Manifestations:
• Common in human bite infections (up to 30%), closed-fist injury infections and skin infections in diabetic and drug-abusers who lick their needles prior to use.
• Periodontal disease, especially in person’s younger than 20 years of age.
• As the source of infection is usually from the oropharynx, most infections are a polymicrobic mix of aerobic and anaerobic organisms.
• Has been isolated in pure culture from several sites including blood, heart valves, synovial fluid, bone, brain and CSF.

Laboratory diagnosis:
• Bacterial culture: grows on blood and chocolate agar, but not selective agars for Gram negative bacteria (for example MacConkey agar).
• Culture characteristics:  Detectable growth requires 48 hrs in a CO2 incubator, small greyish colonies that pit the agar (only half the strains display this characteristic), and emits an odor resembling bleach.

Differential diagnosis: Other Gram negative rod and anaerobic bacterial infections

• Active antibiotics include: Ampicillin, 2nd-3rd generation cephalosporins, tetracyclines, azithromycin and fluoroquinolones.
• Resistant to oxacillin, erythromycin, clindamycin and metronidazole and aminoglycosides.
• Since most infections are polymicrobic, initial therapy is with ampicillin-clavulanate (Augmentin) or ampicillin-sulbactam (Unasyn); for endocarditis Ceftriaxone is recommended.

Prevention and control:
• Good oral hygiene,  avoid human bites and other oral cavity trauma

Related concepts
human bites, HACEK
Eikenella corrodens, Gram stain (CDC Public Health Image Library)
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