A simple double differential centrifugation-wash procedure to rapidly obtain bacterial identification and direct antimicrobial susceptibility testing from positive blood cultures

Abstract

Introduction: This study proposes a simple and rapid method for both bacterial identification and direct antimicrobial susceptibility testing (AST) by using MALDI-TOF and a double differential centrifugation-wash procedure from positive blood cultures.

Methods: Fifty-two positive blood cultures (37 gramnegative bacilli and 15 grampositive cocci) were studied by two methods for identification and AST: a reference method, and the rapid MALDI-TOF method obtaining a purified pellet by using a double differential centrifugation procedure.

Results: A total of 1101 MIC values (mg/l) were interpreted according to EUCAST clinical breakpoints and compared using the two methods simultaneously. Discrepancies in 81 MIC values (7.35%) were detected. By analyzing standard parameters, we obtained 98.28% essential agreement and 92.65% categorical agreement considering all isolates tested.

Conclusion: This method provides rapid bacterial identification and AST, offering definitive results 24-48h earlier than the conventional method (p<0.001) and improving the turnaround time in blood culture diagnostics, especially in laboratories without 24-h on-call.

Keywords: AST; Blood cultures; Doble centrifugación diferencial; Double differential centrifugation; Hemocultivos; Método rápido; Pellet purificado; Purified pellet; Rapid method.