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Background: Polymicrobial bloodstream infection is a difficult diagnostic and therapeutic situation. Inappropriate antimicrobial empiric treatment is twice as high than in monomicrobial bacteremia and diagnostic test methods (identification, antimicrobial susceptibility testing) are ineffective without a subculture step due to the bacterial mix. This results in a long time to results and poorer outcome.
The aim of the study was to evaluate the contribution of a rapid genotypic method (Unyvero®, Curetis) in managing polymicrobial blood cultures.
Materials/methods: 62 polymicrobial blood cultures (one per patient) were prospectively assessed at the academic hospital of Nice (France) with the methods in use in the laboratory (MALDI-TOF mass spectrometry, disk diffusion method) and with Unyvero BCU® application (time to results <5h). Additionally, 30 bottles were spiked with a mix of 2 bacteria that comprised at least one multi-drug resistant microorganism (ESBL, OXA-48, KPC, mecA), and bottles were assessed with the same protocol. Agreement between the 2 methods for identification and antimicrobial resistance detection was determined and time to results were compared.
Results: In the prospective study, 52/62 blood cultures were detected polymicrobial with the BCU® cartridge. All the bacteria of the mix and at least one micro-organism were correctly identified at least at the genus level for 41 (66%) and 58 (94%) blood cultures, respectively. A total of 82% and 53% of bacteria (n=144) were correctly identified at the genus level and species level, respectively, 6% were erroneously identified. Taxa absent from the BCU® panel were the most frequent cause of bacterial detection default (anaerobes, Morganella). Mechanisms of resistance to betalactams were correctly detected for 94% of the bacteria, but neither 1/5 ESBL nor overproduction of cephalosporinase was detected (7 cases). In the spiking study, 73% (17/22) ESBL, and all OXA-48 (n=14), KPC (n=3) and mecA (n=5) were correctly detected. BCU® results (identification, resistance detection) were correct for 57% of the polymicrobial blood cultures. Time to results was reduced by 48h (median) and 119h (percentile 95).
Conclusions: these promising results show that advanced diagnosis can aid to timely document polymicrobial bacteremia and to adjust empiric therapy, but identification and resistance panels should prior be extended.
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