Early Detection of Antibiotic Resistance in Positive Blood Cultures: A Study from a Tertiary Care Center in India

Background and objectives: Conventional culture and sensitivity methods take around 48 hours to generate antibiotic sensitivity results after a blood culture is flagged as positive by automated systems. However, it is imperative to initiate early targeted antibiotic therapy for effective management of sepsis and to reduce morbidity, mortality, and cost of treatment. This study aimed to evaluate the direct sensitivity test (DST) as a potential tool to obtain quicker antibiotic susceptibility results from positive BacT/ALERT blood culture vials and the VITEK-2 system (the reference method). Methods: Blood culture bottles flagged as positive by BacT/ALERT were Gram-stained. Cultures with polymicrobial growth were excluded from the study. The isolates were then simultaneously cultured and processed for the DST using the disk diffusion method. Agreements or errors were interpreted according to the Clinical and Laboratory Standards Institute’s guidelines. Results: Among 76 Gram-positive isolates, we observed 99.2% essential agreement between the DST and AST. The rate of minor and major errors was 4.04% and 1.18%, respectively. Among 75 Gram-negative isolates, we observed 98.99% essential agreement between the DST and AST. The rate of minor and major errors was 4% and 2%, respectively. No very major error was seen in either Gram-negative or -positive isolates. Conclusions: The DST results are available earlier than the AST results, which can ultimately help in the early initiation of targeted antibiotic therapy.