Bacterial Bloodstream Infections in Cardiac Patients: Microbiological Spectrum, Antimicrobial Susceptibility Patterns, and Biomarker Correlation Analysis at a Cardiac Tertiary Care Centre

INTRODUCTION: Bloodstream infections (BSIs) in cardiac patients represent a significant clinical challenge with substantial morbidity and mortality. Understanding the microbiological profile and biomarker patterns in this high-risk population is crucial for optimizing treatment strategies and infection prevention measures. METHODS A retrospective observational study was conducted analyzing patient data from 1st November 2024 to 31st October 2025 at a tertiary cardiac care centre in Karachi, Pakistan. Blood cultures from 113 cardiac inpatients with BSI were analyzed for bacterial identification and susceptibility patterns. Procalcitonin (PCT) and C-reactive protein (CRP) levels were measured simultaneously with microbiological investigation. Correlation analysis between biomarkers and pathogen types was performed using both Pearson and Spearman correlation coefficients. RESULTS One hundred and thirteen bacterial bloodstream isolates were identified with gram-negative bacteria predominating (63.7%, n = 72) over gram-positive organisms (36.3%, n = 41). Escherichia coli was the most prevalent pathogen (17.7%, n = 20), followed by Acinetobacter species (9.7%, n = 11) and Enterobacter species (8.8%, n = 10). Multidrug-resistant organisms accounted for 16.8% (n = 19) of isolates, with Vancomycin-Resistant Enterococcus (8.8%) and Methicillin-Resistant Staphylococcus aureus (8.0%) being the most common. Gram-negative bacteria demonstrated higher mean PCT levels (16.60 ng/mL) compared to gram-positive bacteria (12.24 ng/mL), though not statistically significant (p = 0.094). CRP levels were similarly elevated in both groups (gram-negative: 138.18 mg/L vs gram-positive: 118.09 mg/L, p = 0.216). Spearman correlation analysis revealed a statistically significant correlation between PCT and CRP (ρ = 0.444, p < 0.001) overall, with stronger correlation in gram-positive infections (ρ = 0.510) compared to gram-negative infections (ρ = 0.372). CONCLUSION This study confirms the critical importance of understanding local microbiological epidemiology and biomarker patterns in cardiac patients with BSI, providing evidence-based guidance for empirical antimicrobial therapy, infection prevention strategies, and diagnostic algorithm optimization in tertiary cardiac care settings. PCT and CRP both serve as valuable biomarkers in this population, with their combined use potentially enhancing diagnostic accuracy, supporting their complementary role in sepsis management and antimicrobial stewardship in cardiac patients.