What is the significance of Gram-positive bacilli in blood culture?

From the Guidelines

Gram-positive bacilli in blood cultures require prompt identification and appropriate antimicrobial therapy, with initial empiric treatment including vancomycin and coverage for gram-negative bacilli, based on the local antibiogram 1.

Key Considerations

• Initial empiric treatment should include vancomycin 15-20 mg/kg IV every 8-12 hours (adjusted based on renal function) plus piperacillin-tazobactam 4.5g IV every 6-8 hours or a carbapenem like meropenem 1g IV every 8 hours.
• Common gram-positive bacilli in blood cultures include Bacillus species, Listeria monocytogenes, Corynebacterium species, and Clostridium species.
• Listeria requires specific coverage with ampicillin 2g IV every 4 hours, often combined with gentamicin 5-7 mg/kg IV daily.

Duration and Source Control

• Duration of therapy typically ranges from 7-14 days depending on the pathogen, source of infection, and clinical response.
• Removal of any potential sources such as central venous catheters is essential if they're suspected to be the infection source.
• For patients with CRBSI due to less virulent microbes, such as Bacillus species, catheters should generally be removed after blood culture contamination is ruled out on the basis of multiple positive culture results, with at least 1 blood culture sample drawn from a peripheral vein 1.

Clinical Correlation

• Gram-positive bacilli may represent true infection or contamination, so clinical correlation with patient symptoms, multiple positive cultures, and identification of the specific organism are crucial for determining the significance of these findings.
• If a catheterized patient has a single positive blood culture that grows coagulase-negative Staphylococcus species, then additional cultures of blood samples obtained through the suspected catheter and from a peripheral vein should be performed before the initiation of antimicrobial therapy and/or catheter removal 1.

From the Research

Gram Positive Bacilli in Blood Culture

• Gram positive bacilli in blood culture can be caused by various bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) 2, 3, 4
• The choice of empiric antibiotic therapy for gram positive bacilli in blood culture should consider the likely etiologies and anticipated resistance patterns 2, 3
• Current diagnostic and treatment guidelines suggest that all seriously ill patients in whom infection is suspected undergo a comprehensive work-up (e.g., blood, urine, sputum cultures) to confirm the etiology prior to initiation of antibiotic therapy 2

Treatment Options

• Penicillin, cloxacillin, and erythromycin can cover 90 per cent of Gram-positive infections 5
• Vancomycin, linezolid, and daptomycin are effective against multi-drug-resistant, gram-positive pathogens, including MRSA 2, 3, 6, 4
• Linezolid has been shown to be a potential first-line drug against MRSA bacteremia, with comparable effectiveness and safety to vancomycin, teicoplanin, or daptomycin 4

Antibiotic Resistance

• Antibiotic resistance is a growing concern, and the use of broad-spectrum antibiotics can encourage the emergence of resistant bacteria 2, 3, 6
• Strategies to control the emergence of resistance include the use of narrow-spectrum antibiotics and the development of new antibiotics with activity against resistant organisms 5, 6