Eikenella

Eikenella is a small genus of Gram-negative, non-spore-forming rods. The best-known species is Eikenella corrodens, a member of the normal human oral and upper respiratory tract microbiota. It is commonly involved in infections arising from human oral contact, including clenched-fist injuries and other bite wounds, dental and periodontal infections, and it often participates in polymicrobial infections. Invasive disease can include endocarditis, bacteremia, osteomyelitis, septic arthritis, and thoracic or intra-abdominal infections, particularly in patients with predisposing conditions.

Laboratory and culture features: Eikenella corrodens is a slow-growing, fastidious organism that grows on standard laboratory media such as blood agar but may require enriched, CO2-enriched incubation. Colonies are small, greyish, and non-hemolytic, with a characteristic tendency to corrode or pit the agar, which inspired the species name corrodens. It is typically oxidase-negative.

Treatment and antimicrobial susceptibility: Penicillin monotherapy is often ineffective due to beta-lactamase production by some strains. Effective options include beta-lactam/beta-lactamase inhibitor combinations (such as ampicillin-sulbactam or amoxicillin-clavulanate), certain cephalosporins, and other agents such as doxycycline, tetracyclines, or fluoroquinolones. Empiric therapy should cover oral flora and anaerobes when appropriate, with adjustment based on culture results.

Taxonomy and clinical relevance: Eikenella corrodens is the principal clinically relevant species in humans. The genus is associated with the HACEK group of fastidious Gram-negative bacilli and is linked to endocarditis and various other infections, particularly in the context of oral-tissue injury or dental disease. Diagnosis relies on culture and, when available, molecular methods.