From the Guidelines
Coryneform bacteria are usually considered contaminants in blood cultures, but clinical judgment is necessary to determine their significance, as approximately 70-80% of coryneform isolates represent contamination rather than true bacteremia, according to the most recent evidence 1. When evaluating a positive blood culture with coryneform bacteria, clinicians should consider several factors:
- whether multiple cultures are positive with the same organism
- the patient's clinical presentation
- presence of prosthetic devices
- and immune status. True infections typically require treatment with vancomycin (1g IV every 12 hours) or daptomycin (6mg/kg IV daily), as many coryneform species show resistance to beta-lactams, as noted in the guidelines for the diagnosis and management of intravascular catheter-related infection 1. If contamination is suspected, no antibiotic treatment is needed, but improved blood collection techniques should be implemented to reduce future contamination rates, as emphasized in the american society for microbiology evidence-based laboratory medicine practice guidelines to reduce blood culture contamination rates: a systematic review and meta-analysis 1. The significance of coryneform bacteria in blood cultures should be determined on a case-by-case basis, taking into account the patient's clinical context and the results of multiple blood cultures, as recommended by the infectious diseases society of america 1. In general, the management of coryneform bacteria in blood cultures requires a careful balance between treating potential true infections and avoiding unnecessary antibiotic use, which can contribute to antimicrobial resistance and other adverse outcomes, as highlighted in the guidelines for the management of adult lower respiratory tract infections 1. Therefore, clinicians should approach the diagnosis and management of coryneform bacteria in blood cultures with caution and consider the latest evidence-based guidelines and recommendations 1.
From the Research
Coryneform Bacteria in Blood Cultures
- Coryneform bacteria can be both contaminants and causative agents of serious infections in blood cultures 2, 3, 4, 5.
- Studies have shown that certain species of Corynebacterium, such as Corynebacterium jeikeium and Corynebacterium striatum, are more likely to be associated with true infections, while others, like Corynebacterium afermentans, are more commonly contaminants 3.
- The identification of the species and determination of its antibiotic sensitivity are crucial in distinguishing between contamination and true infection 2, 4, 5.
- Vancomycin is often the most active antimicrobial agent against coryneform bacteria, but resistance can occur, emphasizing the need for accurate identification and susceptibility testing 2, 4, 5.
Contamination vs. True Infection
- A single positive blood culture with Corynebacterium does not necessarily exclude true infection, such as infective endocarditis 3.
- Clinical features, such as underlying diseases, presence of invasive devices, and patient outcomes, can help differentiate between contamination and true infection 2, 3.
- The species of Corynebacterium isolated can also provide clues about the likelihood of true infection or contamination 3.
Clinical Implications
- Coryneform bacteria should be considered as potential pathogens in blood cultures, particularly in immunocompromised patients or those with underlying diseases 2, 3, 4.
- Empiric therapy with vancomycin may not always be appropriate, and accurate identification and antibiotic susceptibility testing are essential for guiding treatment 6, 5.