Rapid microbiological tests for bloodstream infections due to multidrug resistant Gram-negative bacteria: therapeutic implications

Background: Treating severe infections due to multidrug-resistant Gram-negative bacteria (MDR-GNB) is one of the most important challenges for clinicians worldwide, partly because resistance may remain unrecognized until identification of the causative agent and/or antimicrobial susceptibility testing (AST). Recently, some novel rapid test for identification and/or AST of MDR-GNB from positive blood cultures or the blood of patients with bloodstream infections (BSIs) have become available. Objectives: The objective of this narrative review is to discuss the advantages and limitations of different rapid tests for identification and/or AST of MDR-GNB from positive blood cultures or the blood of patients with BSI, as well as the available evidence on their possible role to improve therapeutic decisions and antimicrobial stewardship. Sources: Inductive PubMed search for publications relevant to the topic. Content: The present review is structured in the following way: (a) rapid tests on positive blood cultures; (b) rapid tests directly on whole blood; (c) therapeutic implications. Implications: Novel molecular and phenotypic rapid tests for identification and AST show the potential for favourably influencing patients' outcomes and results of antimicrobial stewardship interventions by reducing both the time to effective treatment and the misuse of antibiotics, although the interpretation about their impact on actual therapeutic decisions and patients' outcomes is still complex. Factors such as feasibility and personnel availability, as well as the detailed knowledge of the local microbiological epidemiology, need to be considered very carefully when implementing novel rapid tests in laboratory workflows and algorithms. Providing high-level, comparable evidence on the clinical impact of rapid identification and AST is becoming of paramount importance for MDR-GNB infections, since in the near future rapid identification of specific resistance mechanisms could be crucial for guiding rapid, effective, and targeted therapy against specific resistance mechanisms.