Publication:

Effect of charcoal supplementation on the accuracy of direct antimicrobial susceptibility testing from blood cultures for key Gram-negative bacilli: an in vitro evaluation

Background Gram negative bacilli such as Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa are major causes of bloodstream infection and are   associated with high mortality rates in critical care settings. Rapid antimicrobial susceptibility testing (AST) directly from positive blood cultures can reduce diagnostic turnaround time and improve patient management. To evaluate the in vitro performance of direct antimicrobial susceptibility testing from blood culture systems, with and without charcoal supplementation, for Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa.

Methods In this study, using clinical isolates from various blood culture systems, Brain Heart Infusion broth (BHI), BHI with charcoal (BHI-C), Tryptic Soy Broth (TSB) and TSB with charcoal (TSB-C). DST was performed directly on the positive broth samples using disk diffusion, and the results from each medium type were compared.

Result Charcoal supplementation significantly increased mean zone diameters for most antibiotics across all organism. TSB-C demonstrated consistently higher susceptibility reading compared to other media.

Conclusion Direct AST using TSB supplemented with charcoal enhances susceptibility accuracy and could be adopted in laboratories lacking automated AST systems for rapid bloodstream infection management.