Direct Antimicrobial Susceptibility Testing from Positive Blood Culture Bottles in Cairo University Hospitals

Background: Rapid identification of suitable antibiotic treatment is vital for patients with bloodstream infections. Standard methods of antimicrobial susceptibility testing (AST) involve subculture of bacteria from positive blood culture bottles, which can delay results. This study aims to evaluate accuracy of direct antimicrobial susceptibility testing (dAST) performed on positive blood culture bottles, compared to the gold standard disk diffusion method. Methodology: A cross-sectional diagnostic study was performed on blood cultures samples that were collected from inpatients referred to the Central Microbiology Laboratories of Kasr Al-Ainy University Hospitals during the period from November 2023 to May 2024. Overall, 155 positive blood cultures for Gram negative bacteria were isolated and were subjected to dAST using the disk diffusion method. The results were compared with standard AST performed after subculture to solid media. Results: Mean age of the included patients was 50.1±14.3 years. 56.8% were ICU patients. While the most common cause of admission was sepsis accounting for 34.2%. The isolated organisms were 148 (95.5%) Klebsiella and 7 (4.5%) E-coli of the studied samples. The dAST method showed a high overall agreement (97.4%) with the standard AST method. While minor, major and very major errors rates were 0%, 1.7% and 0.8% respectively. Conclusion: dAST from positive blood culture bottles significantly reduces the turnaround time, potentially allowing for earlier optimization of antimicrobial therapy. The high agreement rate between direct and standard AST methods supports the reliability of dAST as a valuable tool in clinical microbiology laboratories for managing bloodstream infections more effectively.