261 Towards precision medicine in sepsis bacteria), the presence of PCR inhibitors, including interference due to high levels of human DNA. Several commercial assays have been developed (Table 2) [7, 9, 13-15, 23-26]. These tests have limits such as high costs of equipment and reagents and the detection of circulating microbial DNA (the so-called DNAemia), which may not be synonymous with infection. A pitfall of rapid molecular-based diagnostic tests for bacterial pathogens is that most of them usually provide little information on antimicrobial susceptibility, especially for Gram-negative bacteria. However, a few phenotypic tests have been developed for the rapid evaluation of antimicrobial susceptibility, such as MALDI-TOF mass spectrometry and chromogenic tests for the detection of β-lactam resistance (i.e., ESBL- and carbapenemase-producing Enterobacteriaceae), which could be used on positive BCs [21, 27]. A novel and unique approach is the Accelerate Pheno system (Accelerate Diagnostics) that allows identification of bacteria and fungi (by FISH) as well as phenotypic antimicrobial susceptibility testing (AST) (by morphokinetic cellular analysis) on positive BCs [28-30]. Promising new advanced tools for AST are evolving rapidly, which may be beneficial in sepsis management. A recently developed point-ofcare susceptibility test (based on direct single-cell imaging) can determine Escherichia coli ciprofloxacin susceptibility directly in 49 urine samples, with a total turn-around time of 30 minutes [31]. Furthermore, AST results can be obtained by using ultrafast digital nucleic acid quantification to measure the phenotypic response of E. coli in urine samples exposed to an antibiotic, also within 30 minutes [32]. Although some molecularbased RDTs can detect antimicrobial resistance, they are not (yet) able to quantify the extent of susceptibility (e.g. to measure antibiotic minimum inhibitory concentrations), which may be essential to develop tailored antibiotic dosing strategies. In conclusion, RDT have become useful tools for the diagnosis of sepsis, but in their current status they complement rather than replace BCs. Also, their clinical and economic benefits need to be further investigated. Before implementing RDTs in clinical practice, healthcare institutions should first optimize the use of BC diagnostics. The optimal BC diagnostic algorithm will vary between institutions, according to patient types, local pathogen epidemiology, including local resistance patterns, and antimicrobial prescribing and stewardship policies [12]. Next-generation sequencing (NGS) technologies will likely be a valuable tool for the diagnosis of BSIs in the near future [33], although this approach is presently too time-consuming (~30 hours) [34]. 11
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