A Comparative Study of Standard and Direct Susceptibility Testing From Positive Blood Cultures at a Tertiary Care...

Sepsis is one of the leading causes of death globally. Standard antimicrobial susceptibility testing (AST) takes around 48 hours to get results from a positive blood culture bottle. Advanced diagnostic tools for AST are not available in most of the laboratories in developing countries. Therefore, performing a direct susceptibility testing (DST) might help to reduce turnaround time by 24 hours, reducing high mortality in patients with septicemia.

The study aimed to evaluate the accuracy of DST from positive blood culture broth by comparing categorical agreement and errors against the standard AST of the isolates.

Blood culture bottles flagged as positive by the automated system between January 2024 and December 2024 in a tertiary hospital in Bangladesh were included in this cross-sectional study. Identification of organisms and AST were performed using both DST and standard AST methods, according to the Clinical and Laboratory Standards Institute's guidelines. The results of the two methods were compared for agreement or errors.

A total of 100 bacteria were detected by DST and standardized AST method from the positive blood culture bottles, where Salmonella typhi (38%) was the most prevalent Gram-negative bacterium, and coagulase-negative Staphylococci were the most common Gram-positive bacteria (26%). When compared to the standard AST, categorical agreements of DST were > 93% for Staphylococcus species, Salmonella typhi, Escherichia coli, Klebsiella, Enterobacteri, and Pseudomonas species. The overall categorical disagreements for these organisms were within acceptable limits.

DST from positive blood culture broth can reduce turnaround time and enable earlier initiation of antibiotic therapy in septicemic patients.