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

Abstract

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(R) II, was evaluated in four clinical microbiology laboratories. MethodsPositive blood culture samples (n=801) were processed using the rapidBACpro(R) II kit and then compared with routine gold standard. A subset of monomicrobial BCs (n=560) were analyzed in parallel with the Sepsityper(R) kit (Bruker Daltonics, Bremen, Germany) and compared with the rapidBACpro(R) II kit. In addition, the rapidBACpro(R) 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(R) 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(R) kit yielded higher rates of correct species-level identification provided by the rapidBACpro(R) 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(R) 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.