Infectious Disease and Microbiology – Corynebacterium Species

Overview

Non-diphtherial Corynebacterium species are aerobic Gram-positive bacilli that are usually low-virulence organisms but can occasionally cause serious invasive disease. Important species include C. bovis, C. pilosum, C. pseudodiphtheriticum, C. striatum, and C. xerosis, among others.

These organisms are uncommon causes of infection, but they become more clinically significant in patients with neutropenia, prosthetic devices, or underlying cardiac disease.

Microbiologic Characteristics

Corynebacterium species are:

• Aerobic

• Gram-positive

• Bacillary organisms

Many species can colonize the skin or mucosal surfaces, which means that positive cultures must sometimes be interpreted carefully to distinguish true infection from contamination or colonization.

Epidemiology

These species are rare causes of human infection.

Clinically significant disease is more likely in patients with:

• Neutropenia

• Prosthetic heart valves

• Other implanted prosthetic material

• Severe underlying illness

• Prolonged hospitalization

Endocarditis

Non-diphtherial Corynebacterium species can cause infective endocarditis involving either:

• Native heart valves

• Prosthetic heart valves

Prosthetic valve infection is especially important because organisms may adhere to foreign material and become difficult to eradicate with antibiotics alone.

Septicemia

Septicemia is uncommon but occurs more frequently in neutropenic patients.

Patients may present with:

• Fever

• Chills

• Hypotension

• Persistent bacteremia

• Clinical evidence of sepsis

Repeated recovery of the same Corynebacterium species from blood cultures increases the likelihood that the isolate represents true infection rather than contamination.

Respiratory Tract Infections

These organisms can occasionally cause:

• Pneumonia

• Tracheitis

• Other respiratory tract infections

Respiratory disease is more likely in debilitated, hospitalized, or immunocompromised patients.

Prosthetic Material Infection

Corynebacterium species may infect implanted or prosthetic material.

Examples include:

• Prosthetic heart valves

• Vascular devices

• Orthopedic hardware

• Other implanted foreign bodies

Because biofilm formation and persistent colonization may occur, antimicrobial therapy alone may not always be sufficient.

Diagnosis

Diagnosis is made by culture from the appropriate clinical specimen.

Depending on the infection, samples may include:

• Blood cultures

• Respiratory specimens

• Tissue samples

• Prosthetic-device cultures

• Other sterile-site specimens

Clinical interpretation is important because some Corynebacterium species may be dismissed incorrectly as contaminants.

Treatment of Endocarditis

For severe endocarditis, a regimen described in the source is:

Vancomycin plus an aminoglycoside

This combination may be used initially in serious infection while awaiting susceptibility results.

Prosthetic Material Removal

When infection involves prosthetic material, removal of the infected device or prosthesis is frequently necessary.

Persistent infection despite apparently appropriate antimicrobial treatment should increase suspicion that the foreign material is acting as a continuing source.

Additional Antimicrobial Options

Therapy may need to be modified according to:

• Clinical response

• Site of infection

• Species identification

• In vitro susceptibility testing

Potential alternative agents include:

• Penicillin G

• Tetracycline

• Macrolides

• Rifampicin

• First-generation cephalosporins

• Teicoplanin

Treatment should be individualized because susceptibility patterns may vary among species.

High-Yield Clinical Pattern

Prosthetic valve or implanted device

• ●

Persistent bacteremia with a Corynebacterium species

• ●

Failure to clear infection with antibiotics alone

→ Consider true invasive Corynebacterium infection with infected prosthetic material

Exam Essentials

Genus: Corynebacterium

Type: Aerobic Gram-positive bacillus

Overall frequency: Rare cause of infection

Important syndromes: Endocarditis, septicemia, pneumonia, tracheitis, prosthetic-device infection

High-risk group for septicemia: Neutropenic patients

Diagnosis: Culture

Serious endocarditis treatment: Vancomycin plus an aminoglycoside

Important source-control measure: Removal of infected prosthetic material

Alternative agents: Penicillin G, tetracyclines, macrolides, rifampicin, first-generation cephalosporins, or teicoplanin

Key clinical pearl: When a non-diphtherial Corynebacterium species is repeatedly isolated from blood in a patient with a prosthetic valve, implanted device, or neutropenia, it should not automatically be dismissed as a contaminant.