Evaluation of the rapidBACpro® II kit for the rapid identification of microorganisms directly from blood cultures using MALDI-TOF MS

ObjectivesIdentification of microorganisms directly from blood cultures (BCs) using MALDI-TOF MS has shown to be the application with most impact in this methodology. In this study, a novel commercial method, the rapidBACpro® II, was evaluated in four clinical microbiology laboratories.MethodsPositive blood culture samples (n=801) were processed using the rapidBACpro® II kit and then compared with routine gold standard. A subset of monomicrobial BCs (n=560) were analyzed in parallel with the Sepsityper® kit (Bruker Daltonics, Bremen, Germany) and compared with the rapidBACpro® II kit. In addition, the rapidBACpro® II kit was also compared with two different in-house methods.ResultsOverall, 80.0% of the monomicrobial isolates (609/761) were correctly identified by the rapidBACpro® II kit at the species level (92.3% of the Gram negative and 72.4% of the Gram positive bacteria). The comparison with the Sepsityper® kit yielded higher rates of correct species-level identification provided by the rapidBACpro® II kit for all categories (p>0.0001) except for yeasts identified with score values >1.7. It also proved superior to the ammonium chloride method (p>0.0001) but the differential centrifugation method allowed higher rates of correct identification for Gram negative bacteria (p>0.1).ConclusionsThe rapidBACpro® II kit allowed a high rate of microorganisms correctly identified. The percentage of accurate species-level identification of Gram positive bacteria was particularly noteworthy in comparison with other commercial and in-house methods. This fact was especially interesting in the case of Staphylococcus sp. and Streptococcus sp. in order to elucidate their clinical impact, for example in device-associated bacteremia.