Comparative analysis of antimicrobial susceptibility testing: Conventional versus direct from the blood culture bottle in a tertiary care center

Objectives: The objective of the study is to evaluate the concordance, turnaround time (TAT), and clinical implications of direct antimicrobial susceptibility testing (AST) performed from positive BacT/ALERT ® blood culture bottles compared with conventional AST. Materials and Methods: A prospective study was conducted in the Microbiology Department of UCMS and GTB Hospital, including 250 positive blood cultures from patients with suspected bloodstream infections. Direct AST and conventional AST were performed according to Clinical & Laboratory Standards Institute (CLSI) guidelines. Categorical agreement (CA), TAT, and error rates were assessed. Statistical analysis: Descriptive statistics were used. Continuous variables (TAT) were compared using the Student’s t -test. CA between methods was evaluated using the Chi-square test with degrees of freedom and p values reported. Results: Enterobacterales showed 94.4-99.4% CA, and non-fermenters demonstrated 92.8-100% agreement, with all error rates within CLSI-acceptable limits. Direct AST reduced mean TAT from 28 h (range: 18-32 h) to 9.7 h (range: 8-12.5 h). Direct AST demonstrated the greatest reduction in turnaround time in bloodstream and respiratory infection samples. Conclusions: Direct AST demonstrated high concordance and significantly reduced TATs compared with conventional AST. It enables earlier targeted therapy and supports antimicrobial stewardship.