What Gram‑positive organisms are likely causing a catheter‑related bloodstream infection in a 67‑year‑old male with chronic kidney disease who has fever and chills during dialysis, given growth on blood agar but no growth on MacConkey agar and negative peripheral blood cultures?

Likely Organism: Gram-Positive Cocci, Most Probably Coagulase-Negative Staphylococci or Staphylococcus aureus

The growth pattern—positive on blood agar but no growth on MacConkey agar from the internal jugular catheter—indicates a Gram-positive organism, with coagulase-negative staphylococci (particularly S. epidermidis) and Staphylococcus aureus being the most likely culprits in this dialysis patient with catheter-related bloodstream infection. 1, 2

Microbiological Interpretation

• MacConkey agar is selective for Gram-negative bacteria, so the absence of growth on this medium effectively rules out Gram-negative organisms such as Pseudomonas aeruginosa, E. coli, or Klebsiella species. 3

• Blood agar supports growth of both Gram-positive and Gram-negative organisms, so positive growth here combined with negative MacConkey indicates a Gram-positive pathogen. 3

• The differential growth pattern (positive catheter culture, negative peripheral blood culture) is highly suggestive of catheter-related bloodstream infection (CRBSI) rather than a primary bacteremia from another source. 1

Most Likely Organisms in Hemodialysis CRBSI

Coagulase-Negative Staphylococci (CoNS)

• CoNS, particularly S. epidermidis, account for a substantial proportion of dialysis catheter infections and are the most common Gram-positive organisms isolated in many series. 3, 4

• CoNS infections often present with atypical or less dramatic symptoms compared to S. aureus—this patient has fever and chills, but CoNS can still present this way. 5

• Methicillin-resistant strains (MRSE) are common in dialysis populations, so empirical vancomycin coverage is appropriate. 6

Staphylococcus aureus

• S. aureus is the second most common Gram-positive organism causing CRBSI in hemodialysis patients and is associated with more severe clinical presentations. 2, 5, 3

• Patients with S. aureus CRBSI typically present with fever, rigors, and hemodynamic instability in >90% of cases, which matches this patient's presentation. 5

• S. aureus CRBSI requires mandatory catheter removal due to higher rates of metastatic complications (endocarditis, osteomyelitis) and lower catheter salvage success rates (40-55%). 1, 6

Other Gram-Positive Organisms

• Enterococci and streptococci are less common but possible causes of Gram-positive CRBSI in dialysis patients. 3

Clinical Significance of Organism Type

• Gram-positive organisms account for approximately two-thirds of all hemodialysis CRBSI cases, with S. epidermidis and S. aureus being predominant. 3

• Recent data show that dialysis catheters have the highest odds of S. aureus CRBSI compared to other catheter types (OR 17.3,95% CI 5.75-52.2). 7

• Gram-positive CRBSI is associated with higher rates of hospitalization and catheter removal compared to Gram-negative CRBSI (adjusted OR 9.34 for hospitalization and 3.47 for catheter removal). 2

Immediate Management Recommendations

Empirical Antibiotic Therapy

• Initiate vancomycin plus Gram-negative coverage immediately (third-generation cephalosporin, carbapenem, or β-lactam/β-lactamase inhibitor) based on local antibiogram, even though the growth pattern suggests Gram-positive infection. 1

• Continue antimicrobial therapy for possible CRBSI given the positive catheter culture and symptomatic presentation (fever, chills), even with negative peripheral cultures. 1

Await Final Catheter Culture Results

• The pending blood agar result from the IJ catheter tip/hub will be critical for confirming the organism and determining definitive management. 1

• If the catheter culture grows the same organism as the catheter-drawn blood culture, this confirms CRBSI by standard definitions. 8

Catheter Management Strategy

If S. aureus is identified:

• Remove the catheter immediately and insert a temporary catheter at a different anatomical site. 1
• Treat for 4-6 weeks if bacteremia persists >72 hours or if metastatic complications develop. 1

If CoNS (e.g., MRSE) is identified:

• Catheter can potentially be salvaged if symptoms resolve within 2-3 days and no metastatic infection is present. 1, 6
• Use antibiotic lock therapy as adjunctive treatment for 10-14 days after each dialysis session if catheter is retained. 1, 6
• Success rates for catheter salvage with MRSE range from 75-84% with appropriate antibiotic lock therapy. 6

Common Pitfalls to Avoid

• Do not dismiss a single positive catheter culture in a symptomatic dialysis patient—this warrants full treatment for CRBSI when peripheral cultures cannot be obtained and no alternative source is identified. 1

• Do not assume CoNS represents contamination in this clinical context—fever, chills, and hemodynamic changes during dialysis strongly indicate true infection rather than contamination. 6, 5

• Do not delay catheter removal if S. aureus is confirmed—attempting catheter salvage with S. aureus carries unacceptably high risks of metastatic complications and treatment failure. 1, 6

• Obtain surveillance blood cultures one week after completing therapy if the catheter is retained, as relapse rates can be significant. 1