title: Saponin promotes rapid identification and antimicrobial susceptibility profiling of Gram-positive and Gram-negative bacteria in blood cultures with the Vitek 2 system.
abstract: The rapid identification and antimicrobial susceptibility testing (AST) of bacteria in clinical blood cultures is crucial to optimise antimicrobial therapy. A previous study involving small sample numbers revealed that the addition of saponin to blood cultures, further referred to as the new method, shortened considerably the turn-around time for the identification and AST of Gram-positive cocci as compared to the current method involving an overnight subculture. Here, we extend previous results and compare the identification and AST of blood cultures containing Gram-negative bacilli by the new and current methods. The identification and AST of 121 Gram-positive and 109 Gram-negative bacteria in clinical monomicrobial blood cultures by the new and current methods and, in the case of Gram-negative bacilli, by direct (no additions) inoculation into an automated system (rapid method) was assessed using the Vitek 2 system. Discrepancies between the results obtained with the different methods were solved by manual methods. The new method correctly identified 88 % of Gram-positive and 98 % of Gram-negative bacteria, and the rapid method correctly identified 94 % of Gram-negative bacteria. The AST for all antimicrobials by the new method were concordant with the current method for 55 % and correct for an additional 9 % of Gram-positive bacteria, and concordant with the current method for 62 % and correct for an additional 21 % of Gram-negative bacilli. The AST by the rapid method was concordant with the current method for 62 % and correct for an additional 12 % of Gram-negative bacilli. Together, saponin-treated monomicrobial blood cultures allow rapid and reliable identification and AST of Gram-positive and Gram-negative bacteria.
authors.affiliation: Dipartimento di Ricerca Traslazionale e delle Nuove Tecnologie in Medicina e Chirurgia, Università di Pisa, Via San Zeno 35-39, 56127 Pisa, Italy. antonella.lupetti@med.unipi.it
authors.forename: A
authors.initials: A
authors.lastname: Lupetti
authors.forename: S
authors.initials: S
authors.lastname: Barnini
authors.forename: P
authors.initials: P
authors.lastname: Morici
authors.forename: E
authors.initials: E
authors.lastname: Ghelardi
authors.forename: P H
authors.initials: PH
authors.lastname: Nibbering
authors.forename: M
authors.initials: M
authors.lastname: Campa
mesh_terms: D016470:Bacteremia / Q000175:diagnosis* / Q000382:microbiology; D015373:Bacterial Typing Techniques / Q000379:methods*; D006090:Gram-Negative Bacteria / Q000145:classification / Q000187:drug effects / Q000302:isolation & purification*; D006094:Gram-Positive Bacteria; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D012503:Saponins; D013048:Specimen Handling / Q000379:methods*; D013997:Time Factors
chemical_list: D012503:Saponins