Evaluation of Vitek-2 and MicroScan ASTs directly from positive blood culture: A cost-effective 24-h reduction for Enterobacterales and staphylococci

Abstract

The reduction of antimicrobial susceptibility testing (AST) time-to-result is a central need, especially in sepsis treatment. The current automated rapid ASTs are still too expensive for many laboratories.We aimed to evaluate three pre-treatment methods for a same-day inoculation on both automated AST platforms available in our laboratory. We tested 100 Enterobacterales or staphylococci positive bottles.We obtained good results with the different methods and instruments. In particular, Vitek-2 showed good performances with Enterobacterales AST when inoculated with bacterial pellet (96.6% categorical agreement - CA-, 93.3% essential agreement - EA). Also short-term incubation colonies for staphylococci AST had acceptable CA (94.2%), even if with 77.5% EA. MicroScan system for staphylococci AST with both short-term incubation and direct blood inoculation reached >95% CA, but 92.5% and 83.6% EA, respectively. On the other hand, Enterobacterales AST showed optimal performances only with bacterial pellet inoculation (97.6% CA). In fact, direct blood inoculation showed not acceptable parameters for several molecules.Both systems allow a 24-h reduction in time-to-result, by using the same instruments of routine activity after rapid and cheap pre-treatments.