Is a single bone marrow culture positive for Resistant Staphylococcus (Staph) hemolyticus, co-infected with Klebsiella pneumoniae, considered significant in a vitally stable patient?

Clinical Significance of Single Bone Marrow Culture Positive for Resistant Staphylococcus haemolyticus

A single bone marrow culture positive for resistant Staphylococcus haemolyticus in the presence of Klebsiella pneumoniae should generally be dismissed as a contaminant in a vitally stable patient, and treatment should focus on the Klebsiella pneumoniae as the true pathogen. 1

Rationale for Dismissing as Contaminant

Coagulase-negative staphylococci, including S. haemolyticus, are weak pathogens that rarely cause rapid clinical deterioration, and a single positive culture in a stable patient typically represents contamination rather than true infection. 1 The Infectious Diseases Society of America guidelines explicitly state that a single blood culture positive for coagulase-negative staphylococci should generally be dismissed as attributable to a contaminant, assuming that a second set of specimens have been drawn with negative culture results 1. This principle extends to bone marrow cultures, where skin flora contamination during specimen collection is common 2, 3.

• In bone marrow specimens, skin flora (including coagulase-negative staphylococci) account for 89% of culture-positive specimens, with at least 36% arising from exogenous contamination during collection or processing 3
• S. haemolyticus is the second most frequently isolated coagulase-negative staphylococcus from clinical specimens, but its clinical significance is primarily in the context of medical device infections and immunocompromised hosts with indwelling catheters 4
• The patient's vital stability strongly argues against true S. haemolyticus bacteremia, as clinically significant infections with this organism typically present with hemodynamic instability or severe sepsis 1

Focus on Klebsiella pneumoniae as True Pathogen

The presence of Klebsiella pneumoniae in the same culture represents the clinically significant pathogen requiring treatment, particularly given its higher virulence and propensity to cause serious infections. 5

• Klebsiella pneumoniae is a well-established pathogen capable of causing severe infections including bacteremia, and its presence in bone marrow culture warrants definitive antimicrobial therapy 5
• For resistant K. pneumoniae, carbapenems (meropenem or imipenem-cilastatin) remain the gold standard treatment, with treatment duration of 10-14 days for documented infections 5
• If the K. pneumoniae is ESBL-producing, Group 2 carbapenems should be used for the full treatment course, and fluoroquinolones should be avoided even if susceptibility testing suggests otherwise due to high resistance rates 6
• For carbapenemase-producing K. pneumoniae, early use of polymyxin-colistin or tigecycline should be considered 1, 5

Clinical Decision Algorithm

Follow this approach to determine clinical significance:

1. Assess patient stability: Vitally stable patients without hemodynamic instability, severe sepsis, or catheter-related infection signs do not require coverage for coagulase-negative staphylococci 1

2. Evaluate for specific indications requiring gram-positive coverage: Only add vancomycin or other gram-positive agents if the patient develops hemodynamic instability, pneumonia, suspected catheter-related infection with chills/rigors, or skin/soft-tissue infection 1

3. Prioritize treatment of K. pneumoniae: Initiate appropriate therapy based on resistance patterns (third-generation cephalosporin for susceptible strains, carbapenem for ESBL producers) 5

4. Do not add vancomycin empirically: Vancomycin is not recommended as a standard part of initial therapy for stable patients, as randomized studies show no significant reductions in duration of fever or overall mortality when added empirically 1

Critical Pitfalls to Avoid

• Do not treat single positive cultures for coagulase-negative staphylococci in stable patients, as this leads to unnecessary vancomycin use and promotes resistance development in Enterococcus species and S. aureus 1
• Avoid delaying appropriate K. pneumoniae therapy while debating the significance of S. haemolyticus, as K. pneumoniae represents the true threat requiring immediate targeted treatment 5
• Do not use fluoroquinolones empirically for K. pneumoniae if the patient received them as prophylaxis or within the past 3-6 months, due to resistance rates of 60-93% in ESBL-producing organisms 6, 5
• Recognize that polymicrobial cultures from bone marrow often reflect contamination during collection, particularly when skin flora is involved alongside a known pathogen 3