Saponin promotes rapid identification and antimicrobial susceptibility profiling of Gram-positive and Gram-negative bact
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ARTICLE
Saponin promotes rapid identification and antimicrobial susceptibility profiling of Gram-positive and Gram-negative bacteria in blood cultures with the Vitek 2 system A. Lupetti & S. Barnini & P. Morici & E. Ghelardi & P. H. Nibbering & M. Campa
Received: 10 September 2012 / Accepted: 8 October 2012 / Published online: 2 November 2012 # Springer-Verlag Berlin Heidelberg 2012
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 Gramnegative 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 Gramnegative 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 % A. Lupetti (*) : S. Barnini : P. Morici : E. Ghelardi : M. Campa Dipartimento di Ricerca Traslazionale e delle Nuove Tecnologie in Medicina e Chirurgia, Università di Pisa, Via San Zeno 35–39, 56127 Pisa, Italy e-mail: [email protected] P. H. Nibbering Center of Infectious Diseases, Department of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands
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.
Introduction Bloodstream infections are one of the leading causes of morbidity and mortality in critically ill patients [1] and place a major burden on healthcare budgets. Despite improvements in the diagnosis, management and survival rates, the incidence of bloodstream infections is increasing, as is the number of associated deaths [2]. Clinicians often initiate presumptive antimicrobial therapy comprising of one or more broad-spectrum antimicrobials prior to accurate diagnosis of the causative agent(s). The main drawbacks
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