Evaluation of direct drug susceptibility testing of blood culture isolates comparing it with conventional disk diffusion testing

Objective: To evaluate a direct antibiotic susceptibility testing method for blood culture. Methods: The cross-sectional comparative study was conducted at the Armed Forces Institute of Pathology, Rawalpindi, Pakistan, from December 2016 to October 2017. Direct antimicrobial susceptibility testing was performed from positive blood culture bottles. Bacterial identification was done by using API 10S. Different antimicrobial panels were employed for Gram-negative rods (GNRs), gram-positive cocci (like suspected Staphylococci and Enterococci). Results were compared with conventional disk diffusion testing and very major, major and minor errors were calculated. Result agreement and kappa coefficient scores were generated for categorical agreement. SPSS 24 was used for data analysis. Results: Of the 101 bacterial isolates, 82(81.2%) were Gram negative rods and 19(18.8%) were Gram-positive cocci. Among 781 bacteria-antibiotic comparisons, the number of very major errors was 3(0.4%), major errors were 7(0.9%) and minor errors were 12(1.5%), while, 759(97.2%) comparisons yielded the same results. The kappa coefficient was 0.946, showing almost perfect agreement. Direct identification of Gram negative rods was successful in 53(64.6%) cases. Conclusion: Direct susceptibility testing of blood culture produced reliable results for majority of the antimicrobials.