Assessing the effectiveness of direct susceptibility testing from positive blood culture broth using the VITEK-2 system

Bloodstream infections (BSIs) are prevalent in intensive care units, often requiring timely diagnosis and treatment. Traditional methods of diagnosing bacteraemia, including Gram staining, subculture, and antibiotic susceptibility testing (AST), can yield results in 12-48 hours. The advent of MALDI-TOF MS has expedited bacterial identification from colonies. Recently, methods to directly identify bacteria from positive blood cultures using MALDI-TOF MS have emerged. This study compared the findings of traditional colony-based AST with the VITEK-2 automated testing technology for direct AST from the blood culture broth. Blood cultures were processed using BacT/Alert Virtuo. Aerobic-positive cultures showing single organism types were subjected to direct identification and susceptibility with VITEK MS and VITEK 2, respectively. The methodology involved lysis centrifugation and on-plate extraction for MALDI-TOF MS identification, followed by AST using VITEK 2. A total of 60 isolates, comprising 44 Gram-negative and 16 Gram-positive bacteria, were included. This study tested 902 drug-bug combinations, revealing better categorical agreement for Gram-negative (93.7%) than Gram-positive organisms, which showed higher error rates, particularly with Vancomycin, Linezolid, and Oxacillin for and Cefepime for . The results highlight that VITEK 2 and MALDI-TOF MS allow identification on the same day and whole panel AST from positive blood cultures, cutting the turnaround time by a day compared to traditional methods. This rapid approach facilitates timely and targeted antimicrobial therapy, potentially improving patient outcomes and antimicrobial stewardship. However, larger studies are needed to validate these findings, especially for Gram-positive isolates.