Eikenella corrodens

Bacteria:

• Gram-negative fastidious facultative anaerobic bacillus; however, it is pleomorphic and could appear in coccobacillary form.
• It is non-motile, non-spore-forming and encapsulated.
• It is a member of the oral, gastrointestinal, and genitourinary flora.

Pathogenicity:

• Adherence – lectin-like protein, pilli
• Ability to aggregate RBC.
• Avoid phagocytosis – extracellular polysaccharide or slime layer.
• Cell wall lipopolysaccharide

Culture and identification:

• Slow-growing, small pin-point colony with a bleach-like smell.
• It is yellow-grey with a small greenish discolouration on the blood agar. 50% of colonies are pitting.
• It can grow aerobically or anaerobically.
• It usually requires hemin (X factor) and carbon dioxide for primary isolation.
• Oxidase positive, catalase-negative (some weakly positive), urease negative, indole negative, reduce nitrate.
• API20E , (API20NE with additional test)
• MALDI ToF

Infection caused by Eikenella:

• Head and neck infection, sinusitis,
• Pulmonary infection, septic emboli
• Endocarditis
• Arthritis, skull infection, vertebral osteomyelitis
• Intraabdominal infection, pancreatic abscesses, liver abscess
• Chorioamnionitis
• Infection after human bite wounds (“clenched-fist injuries”) etc
• Skin infection in IVDUs (skin poppers)

Points to remember

• It is a member of the HACEK group of organisms and can cause endocarditis (especially in IVDUs or prosthetic valves)
• Most infections are polymicrobial.
• The patient often has comorbidities like mental retardation with cerebral palsy,  head and neck malignancies, Down’s syndrome, diabetes, leukaemia, or trauma history.
• Surgical intervention is often required for a successful outcome.

Eikenella corrodens is usually susceptible to:

• Penicillin, amoxicillin
• First-generation cephalosporins – variable susceptibility, reported resistance to cephalexin
• Second and third-generation cephalosporins
• Betalactam-beta-lactamase combination – coamoxiclav and pip-tazobactam
• Tetracyclines
• Fluoroquinolones
• Cotrimoxazole

Non-susceptible to:

• Clindamycin
• Macrolides – erythromycin, clarithromycin etc
• Aminoglycosides – gentamicin, amikacin etc
• Metronidazole.