Infectious Disease and Microbiology – Eikenella corrodens

Overview

Eikenella corrodens is a microaerophilic Gram-negative bacillus that belongs to the HACEK group. It is part of the normal human oral flora but can become pathogenic when introduced into normally sterile tissues.

It is particularly associated with human bite wounds, infections in intravenous drug users, endocarditis, and polymicrobial pulmonary infections.

Microbiologic Characteristics

Eikenella corrodens is characterized as:

• Gram-negative bacillus

• Microaerophilic

• Member of the HACEK group

• Normal inhabitant of the human oral cavity

The HACEK organisms are notable for their association with infective endocarditis.

HACEK Group

The traditional HACEK group consists of:

H – Haemophilus species

A – Aggregatibacter species

C – Cardiobacterium hominis

E – Eikenella corrodens

K – Kingella species

These are Gram-negative organisms associated particularly with infections originating from the oral or upper respiratory flora and with endocarditis.

Epidemiology

E. corrodens occurs worldwide, although clinically significant infection is relatively uncommon.

Because it normally colonizes the mouth, many infections result from introduction of oral flora into deeper tissues.

Normal Oral Flora

An important concept is that E. corrodens is part of the normal oral microbiota.

This explains its strong association with:

• Human bite wounds

• Oral contamination of traumatic wounds

• Head and neck infections

• Some pulmonary infections

• Infective endocarditis

Human Bite-Wound Infection

E. corrodens is a classic pathogen associated with human bites.

Human bite wounds are typically polymicrobial, and E. corrodens may be introduced into the wound together with other organisms from the oral cavity.

Clenched-Fist Injury

A particularly high-yield presentation is the clenched-fist injury, sometimes called a “fight bite.”

This occurs when a person’s fist strikes another person’s teeth, producing a small wound over a metacarpophalangeal joint.

Oral organisms such as E. corrodens may then be inoculated into deeper tissues, potentially resulting in:

• Cellulitis

• Abscess

• Septic arthritis

• Tenosynovitis

• Osteomyelitis

Infection in Intravenous Drug Users

E. corrodens can cause skin and soft-tissue infections in intravenous drug users.

These infections may be polymicrobial, particularly when oral flora contaminate injection equipment or the injection site.

Internal Jugular Vein Thrombophlebitis

E. corrodens has also been associated with internal jugular vein thrombophlebitis.

This represents a potentially serious invasive infection involving thrombosis and inflammation of the internal jugular vein.

Endocarditis

Because E. corrodens belongs to the HACEK group, it is an important though uncommon cause of infective endocarditis.

Clinical manifestations may include:

• Persistent fever

• Constitutional symptoms

• New or changing cardiac murmur

• Embolic phenomena

• Other manifestations of valvular infection

Pulmonary Infection

E. corrodens may cause several pulmonary and pleural infections, including:

• Pneumonia

• Lung abscess

• Empyema

These infections are commonly polymicrobial, reflecting the organism’s origin in the oral flora.

Diagnosis

Diagnosis is established by culture of appropriate clinical specimens.

Depending on the syndrome, specimens may include:

• Blood cultures

• Wound cultures

• Abscess material

• Pleural fluid

• Other infected tissue or fluids

Treatment

The source lists the principal treatments as:

Penicillin G

or

Amoxicillin–clavulanate

For human bite wounds, amoxicillin–clavulanate provides useful broad coverage because these infections are frequently polymicrobial.

Additional Treatment Options

Other agents described as potential alternatives include:

• Doxycycline

• Second-generation cephalosporins

• Third-generation cephalosporins

The source also lists aminoglycosides among possible agents.

Treatment of serious infection should ultimately be guided by culture and antimicrobial susceptibility results.

Beta-Lactamase Production

Some strains of E. corrodens produce beta-lactamases.

This possibility should be considered when selecting antimicrobial therapy, particularly if susceptibility results are not yet available.

Important Antibiotic Resistance

A particularly important feature of E. corrodens is its resistance to several antibiotics that might otherwise be considered for skin, oral, or anaerobic infections.

It is characteristically resistant to:

• Metronidazole

• Clindamycin

• Oxacillin

• First-generation cephalosporins

Human Bite Wound – Antibiotic Warning

Because E. corrodens may be present in human bite wounds:

Clindamycin alone should not be relied upon for empiric treatment.

Similarly, first-generation cephalosporins such as cephalexin or cefazolin do not provide reliable Eikenella coverage.

This resistance pattern is a major exam point.

High-Yield Clinical Pattern

Human bite or clenched-fist injury

• ●

Polymicrobial wound infection

• ●

Gram-negative bacillus from normal oral flora

• ●

Resistance to clindamycin and first-generation cephalosporins

→ Think Eikenella corrodens

Another High-Yield Association

HACEK organism

• ●

Subacute infective endocarditis

• ●

Oral flora

→ Consider Eikenella corrodens

Exam Essentials

Organism: Eikenella corrodens

Type: Microaerophilic Gram-negative bacillus

Group: HACEK

Normal habitat: Human oral flora

Classic infection: Human bite wound / clenched-fist injury

Other infections: Skin infection in IV drug users, internal jugular thrombophlebitis, endocarditis, pneumonia, lung abscess, and empyema

Pulmonary infections: Often polymicrobial

Diagnosis: Culture

Treatment: Penicillin G or amoxicillin–clavulanate

Possible alternatives: Doxycycline or second-/third-generation cephalosporins

Beta-lactamase: Some strains produce it

Important resistance: Metronidazole, clindamycin, oxacillin, and first-generation cephalosporins

Key clinical pearl: The classic association is human bite or fight-bite wound + normal oral flora + HACEK Gram-negative bacillus resistant to clindamycin and first-generation cephalosporins = Eikenella corrodens.

Microbiologic Characteristics Eikenella corrodens is characterized as: • Gram-negative bacillus

• Microaerophilic

• Member of the HACEK group

• Normal inhabitant of the human oral cavity The HACEK organisms are notable for their association with infective endocarditis.

HACEK Group The traditional HACEK group consists of: H – Haemophilus species

A – Aggregatibacter species

C – Cardiobacterium hominis

E – Eikenella corrodens

K – Kingella species These are Gram-negative organisms associated particularly with infections originating from the oral or upper respiratory flora and with endocarditis.

Epidemiology E. corrodens occurs worldwide, although clinically significant infection is relatively uncommon. Because it normally colonizes the mouth, many infections result from introduction of oral flora into deeper tissues.

Normal Oral Flora An important concept is that E. corrodens is part of the normal oral microbiota. This explains its strong association with: • Human bite wounds

• Oral contamination of traumatic wounds

• Head and neck infections

• Some pulmonary infections

• Infective endocarditis

Human Bite-Wound Infection E. corrodens is a classic pathogen associated with human bites. Human bite wounds are typically polymicrobial, and E. corrodens may be introduced into the wound together with other organisms from the oral cavity.

Clenched-Fist Injury A particularly high-yield presentation is the clenched-fist injury, sometimes called a “fight bite.” This occurs when a person’s fist strikes another person’s teeth, producing a small wound over a metacarpophalangeal joint. Oral organisms such as E. corrodens may then be inoculated into deeper tissues, potentially resulting in: • Cellulitis

• Abscess

• Septic arthritis

• Tenosynovitis

• Osteomyelitis

Infection in Intravenous Drug Users E. corrodens can cause skin and soft-tissue infections in intravenous drug users. These infections may be polymicrobial, particularly when oral flora contaminate injection equipment or the injection site.

Internal Jugular Vein Thrombophlebitis E. corrodens has also been associated with internal jugular vein thrombophlebitis. This represents a potentially serious invasive infection involving thrombosis and inflammation of the internal jugular vein.

Endocarditis Because E. corrodens belongs to the HACEK group, it is an important though uncommon cause of infective endocarditis. Clinical manifestations may include: • Persistent fever

• Constitutional symptoms

• New or changing cardiac murmur

• Embolic phenomena

• Other manifestations of valvular infection

Pulmonary Infection E. corrodens may cause several pulmonary and pleural infections, including: • Pneumonia

• Lung abscess

• Empyema These infections are commonly polymicrobial, reflecting the organism’s origin in the oral flora.

Diagnosis Diagnosis is established by culture of appropriate clinical specimens. Depending on the syndrome, specimens may include: • Blood cultures

• Wound cultures

• Abscess material

• Pleural fluid

• Other infected tissue or fluids

Treatment The source lists the principal treatments as: Penicillin G or Amoxicillin–clavulanate For human bite wounds, amoxicillin–clavulanate provides useful broad coverage because these infections are frequently polymicrobial.

Additional Treatment Options Other agents described as potential alternatives include: • Doxycycline

• Second-generation cephalosporins

• Third-generation cephalosporins The source also lists aminoglycosides among possible agents. Treatment of serious infection should ultimately be guided by culture and antimicrobial susceptibility results.

Beta-Lactamase Production Some strains of E. corrodens produce beta-lactamases. This possibility should be considered when selecting antimicrobial therapy, particularly if susceptibility results are not yet available.

Important Antibiotic Resistance A particularly important feature of E. corrodens is its resistance to several antibiotics that might otherwise be considered for skin, oral, or anaerobic infections. It is characteristically resistant to: • Metronidazole

• Clindamycin

• Oxacillin

• First-generation cephalosporins

Human Bite Wound – Antibiotic Warning Because E. corrodens may be present in human bite wounds: Clindamycin alone should not be relied upon for empiric treatment. Similarly, first-generation cephalosporins such as cephalexin or cefazolin do not provide reliable Eikenella coverage. This resistance pattern is a major exam point.

High-Yield Clinical Pattern Human bite or clenched-fist injury  ●  Polymicrobial wound infection  ●  Gram-negative bacillus from normal oral flora  ●  Resistance to clindamycin and first-generation cephalosporins → Think Eikenella corrodens

Another High-Yield Association HACEK organism  ●  Subacute infective endocarditis  ●  Oral flora → Consider Eikenella corrodens

Exam Essentials Organism: Eikenella corrodens

Type: Microaerophilic Gram-negative bacillus

Group: HACEK

Normal habitat: Human oral flora

Classic infection: Human bite wound / clenched-fist injury

Other infections: Skin infection in IV drug users, internal jugular thrombophlebitis, endocarditis, pneumonia, lung abscess, and empyema

Pulmonary infections: Often polymicrobial

Diagnosis: Culture

Treatment: Penicillin G or amoxicillin–clavulanate

Possible alternatives: Doxycycline or second-/third-generation cephalosporins

Beta-lactamase: Some strains produce it

Important resistance: Metronidazole, clindamycin, oxacillin, and first-generation cephalosporins

Key clinical pearl: The classic association is human bite or fight-bite wound + normal oral flora + HACEK Gram-negative bacillus resistant to clindamycin and first-generation cephalosporins = Eikenella corrodens.