In the microbiology laboratory, antibiotic susceptibility is traditionally determined using the disk diffusion method on agar medium, directly from a positive blood culture bottle, which requires 18 to 24 hours of incubation. Over the past decade, the turnaround time for antibiotic susceptibility testing has been shortened (down to 7 hours) thanks to rapid diagnostic tools. However, to date, there is no rapid (within 4 to 6 hours) and accurate method for determining the Minimum Inhibitory Concentration (MIC) that would allow for optimized antibiotic treatment beyond the basic susceptibility to a tested drug. This level of precision would be particularly useful in critically ill septic patients, especially in cases of bacteremia caused by Gram-negative bacilli (GNB).
Recent intensive care guidelines have suggested that for β-lactam antibiotics, the therapeutic target in these patients should be a plasma antibiotic concentration between 4 to 8 times the MIC of the administered antibiotic, depending on the bacterium and the drug. MIC thus represents a key determinant for optimizing antibiotic therapy by increasing the likelihood of achieving the pharmacodynamic efficacy targets of β-lactams.
The use of a new instrument, the SPECIFIC REVEAL® Rapid AST system (bioMérieux), which provides not only a full antibiogram but also MIC values for 23 different antibiotics as early as 4 hours after a positive GNB blood culture (Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii), could represent a potential benefit for ICU patients by enabling rapid optimization of antibiotic therapy. This technique was validated by comparison with two reference methods: a precise MIC determination method (broth microdilution, Sensititre, ThermoFisher) and an approximate method (Vitek2, bioMérieux). A 96% correlation was observed across the 23 antibiotics tested. Furthermore, a recent study conducted outside the ICU suggested a clinical impact, with earlier re-evaluation of antibiotic choices in 58% of cases.
