Eikenella corrodens is a fastidious, Gram-negative, facultatively anaerobic, rod-shaped bacterium that naturally inhabits human mucosal surfaces, particularly within the oral cavity, upper respiratory tract, and gastrointestinal system. Although it functions primarily as a commensal organism in healthy individuals, it acts as an opportunistic human pathogen capable of causing severe localized and systemic infections when introduced into normally sterile tissues. Eikenella corrodens is recognized as a core member of the HACEK group, an acronym designating a collection of fastidious Gram-negative bacilli known for causing infective endocarditis. Clinical interest in E. corrodens stems from its distinct microbiological characteristics, including its ability to pit or "corrode" solid agar growth media, its association with human bite wounds, and its presence in mixed polymicrobial infections alongside streptococcal species and anaerobic organisms.
What Is the History and Naming of Eikenella corrodens?
Eikenella corrodens was first identified in 1958 by Danish microbiologist M. Eiken, who isolated the organism from human clinical specimens and initially designated it as Bacteroides corrodens. Eiken observed that colonies of this organism created physical depressions in solid blood agar media, a characteristic phenotypic trait referred to as agar pitting or corrosion. In 1972, microbiologists Jackson and Goodman re-evaluated the biochemical, metabolic, and genetic profiles of the bacterium, determining that it possessed physiological features distinct from the obligately anaerobic genus Bacteroides. Consequently, the organism was reclassified into a newly established genus, Eikenella, named in honor of M. Eiken, with the specific epithet corrodens preserved to highlight its agar-corroding property.Bacteroides rrodens (1958) ──> Re-evaluated by Jackson & Goodman ──> Eikenella corrodens (1972)
What Diseases and Symptoms Are Caused by Eikenella corrodens?
Eikenella corrodenscauses diverse clinical infections, most frequently presenting as soft tissue infections, dental diseases, bone involvement, and cardiovascular complications. The symptoms vary directly according to the anatomical site of infection:
Head and Neck Infections: It contributes significantly to chronic periodontitis, periapical abscesses, head and neck space infections, and sinusitis. Symptoms include localized facial pain, tissue edema, erythema, purulent drainage, and progressive bone destruction around dental structures.
Bite Wound and Traumatic Soft Tissue Infections:E. corrodens is isolated from human bite injuries and "clenched-fist" injuries (occurring when an individual's fist strikes human teeth). Symptoms manifest as rapid localized swelling, intense pain, erythema, low-grade fever, and purulent exudate at the injury site.
Infective Endocarditis: As part of the HACEK group, it causes subacute bacterial endocarditis, targeting damaged or prosthetic heart valves. Symptoms include persistent low-grade fever, fatigue, heart murmurs, night sweats, weight loss, and embolic phenomena.
Osteomyelitis and Septic Arthritis: Local invasion or hematogenous spread leads to bone and joint destruction, particularly in the hand, wrist, or knee joints. Clinical signs include severe joint pain, swelling, restricted range of motion, and localized heat.
Intra-abdominal and Pelvic Abscesses: Infections often occur as part of polymicrobial abscess formation following surgical disruption or trauma to the gastrointestinal tract, presenting with localized abdominal pain, fever, and leukocytosis.
How Is Eikenella corrodens Transmitted?
Transmission of Eikenella corrodens occurs almost exclusively through endogenous translocation or direct contact with human oral secretions:
Endogenous Translocation: The primary route of infection occurs when an individual's normal mucosal barrier is compromised by surgery, dental procedures, mechanical trauma, mucosal ulceration, or underlying malignancy, allowing indigenous oral bacteria to invade sterile deep tissues.
Direct Inoculation via Bite Injuries: Direct transmission happens through human bites or clenched-fist injuries, where the skin barrier is punctured by teeth, inoculating oral fluid directly into subcutaneous tissue, tendon sheaths, or joint capsules.
Fomite and Person-to-Person Contact: Direct salivary exchange (such as shared utensils or dental instruments) can transfer strains between hosts, though exogenous infection rarely causes disease in the absence of mucosal damage.
How Is Eikenella corrodens Diagnosed in a Laboratory?
Diagnosis of Eikenella corrodens relies on isolation from sterile clinical specimens, microscopic evaluation, and advanced diagnostic testing:
Microscopic Morphology: Gram staining of clinical isolates reveals small, slender, straight Gram-negative rods with rounded ends.
Culture and Growth Characteristics:E. corrodens is fastidious, requiring hemin (X factor) for aerobic growth. On sheep blood agar or chocolate agar incubated in a carbon-dioxide-enriched atmosphere, it forms small, translucent colonies after 24 to 48 hours.
Phenotypic Features: Approximately 50% of strains display characteristic agar corrosion, where colonies depress or sink into the agar surface. Cultures emit a distinctive hypochlorite bleach-like odor.
Biochemical Identification: The organism is oxidase-positive, catalase-negative, urease-negative, indole-negative, and nitrate-reduction positive. It is strictly non-saccharolytic, failing to produce acid from carbohydrate fermentation.
Molecular and Diagnostic Methods: Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) and 16S rRNA gene sequencing allow rapid identification when traditional biochemical tests yield ambiguous results.
What Is the Recommended Treatment for Eikenella corrodens?
Treatment of Eikenella corrodens infections involves targeted antimicrobial therapy combined with surgical intervention when abscesses or deep wound inoculations are present:
Surgical Debridement and Drainage
Surgical intervention is required for bite injuries, deep space neck infections, and abscesses. Drainage of purulent fluid and thorough debridement of necrotic tissue reduce bacterial burden and restore local perfusion.
Antimicrobial Susceptibility Profile
E. corrodens exhibits a specific pattern of antimicrobial susceptibility and intrinsic resistance that differentiates it from many other Gram-negative bacilli:
Susceptible Agents: Penicillins (such as ampicillin and amoxicillin-clavulanate), extended-spectrum cephalosporins (ceftriaxone, cefotaxime), carbapenems (imipenem, meropenem), fluoroquinolones (ciprofloxacin, levofloxacin), and tetracyclines (doxycycline).
Resistant Agents:E. corrodens is intrinsically resistant to clindamycin, metronidazole, macrolides (erythromycin), vancomycin, and first-generation cephalosporins (cephalexin). It often demonstrates variable or low susceptibility to aminoglycosides.
How Can Eikenella corrodens Infections Be Prevented?
Prevention of Eikenella corrodens infections relies on maintaining mucosal tissue integrity and following immediate hygiene protocols following traumatic exposures:
Oral Hygiene Practices: Regular brushing, flossing, and professional dental cleanings reduce plaque accumulation and minimize the microbial burden of E. corrodens in the oral cavity.
Immediate Wound Care for Bites: Promptly washing human bite injuries or clenched-fist lacerations with sterile saline and soap removes introduced oral fluids and reduces bacterial density.
Prophylactic Antimicrobials: Administering oral amoxicillin-clavulanate following high-risk human bite wounds provides early targeted coverage against E. corrodens and co-inoculated oral flora.
Surgical Infection Control: Adhering to strict aseptic techniques during oral, maxillofacial, and upper gastrointestinal surgical procedures prevents translocation into sterile tissues.
Microbe Profile
The biological characteristics of Eikenella corrodens are summarized in the profile below:
Gram status: Gram-negative
Shape: Rod-shaped (Bacillus / Coccobacillus)
Spore formation: Non-spore-forming
Motile: Non-motile (exhibits twitching motility via type IV pili on solid surfaces)
Oxygen requirements: Facultative anaerobe
Optimum temperature: 35°C to 37°C
Optimum pH: 7.2 to 7.6
Taxonomic classification
Domain: Bacteria
Kingdom: Pseudomonadati
Phylum:Pseudomonadota
Class: Betaproteobacteria
Order: Neisseriales
Family: Neisseriaceae
Genus: Eikenella
Species: E. corrodens
Reference
Bilos, Z. J., Kucharchuk, A., & Metzger, W. (1978). Eikenella Corrodens in Human Bites. Clinical Orthopaedics and Related Research, &NA;, 320324.https://doi.org/10.1097/00003086-197807000-00049
Henriksen, S. D. (1969). Designation of the type strain of Bacteroides corrodens Eiken 1958. International Journal of Systematic Bacteriology, 19(2), 165–166.https://doi.org/10.1099/00207713-19-2-165
Khaledi, M., Sameni, F., Afkhami, H., Hemmati, J., Asareh Zadegan Dezfuli, A., Sanae, M.-J., & Validi, M. (2022). Infective endocarditis by HACEK: a review. Journal of Cardiothoracic Surgery, 17(1).https://doi.org/10.1186/s13019-022-01932-5 Cited by: 126
Luong, N., Tsai, J., & Chen, C. (2001). Susceptibilities of Eikenella corrodens, Prevotella intermedia, and Prevotella nigrescens Clinical Isolates to Amoxicillin and Tetracycline. Antimicrobial Agents and Chemotherapy, 45(11), 3253–3255.https://doi.org/10.1128/aac.45.11.3253-3255.2001
Patrick, W. D., Brown, W. D., Ian Bowmer, M., & Sinave, C. P. (1990). Infective Endocarditis Due to Eikenella corrodens: Case Report and Review of the Literature. Canadian Journal of Infectious Diseases and Medical Microbiology, 1(4), 139–142.https://doi.org/10.1155/1990/619065
Schmidt, D. R., & Heckman, J. D. (1983). Eikenella corrodens in Human Bite Infections of the Hand. The Journal of Trauma: Injury, Infection, and Critical Care, 23(6), 478–482.https://doi.org/10.1097/00005373-198306000-00006