Abstract
Rapid identification and determination of the antibiotic susceptibility profiles of the infectious agents in patients with bloodstream infections are critical steps in choosing an effective targeted antibiotic for treatment. However, there has been minimal effort focused on developing combined methods for the simultaneous direct identification and antibiotic susceptibility determination of bacteria in positive blood cultures. In this study, we constructed a lysis-centrifugation-wash procedure to prepare a bacterial pellet from positive blood cultures, which can be used directly for identification by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and antibiotic susceptibility testing by the Vitek 2 system. The method was evaluated using a total of 129 clinical bacteria-positive blood cultures. The whole sample preparation process could be completed in <15 min. The correct rate of direct MALDI-TOF MS identification was 96.49% for gram-negative bacteria and 97.22% for gram-positive bacteria. Vitek 2 antimicrobial susceptibility testing of gram-negative bacteria showed an agreement rate of antimicrobial categories of 96.89% with a minor error, major error, and very major error rate of 2.63, 0.24, and 0.24%, respectively. Category agreement of antimicrobials against gram-positive bacteria was 92.81%, with a minor error, major error, and very major error rate of 4.51, 1.22, and 1.46%, respectively. These results indicated that our direct antibiotic susceptibility analysis method worked well compared to the conventional culture-dependent laboratory method. Overall, this fast, easy, and accurate method can facilitate the direct identification and antibiotic susceptibility testing of bacteria in positive blood cultures.
Highlights
Bloodstream infection is one of the leading causes of death worldwide (Adhikari et al, 2010; Morgenthaler and Kostrzewa, 2015)
New serum separator tubes (Moussaoui et al, 2010; Stevenson et al, 2010; Wimmer et al, 2012), detergent reagents (Ferroni et al, 2010; Yonetani et al, 2012; Morgenthaler and Kostrzewa, 2015), centrifugation conditions, filters (Fothergill et al, 2013), and commercial kits (La Scola and Raoult, 2009; Juiz et al, 2012; Saffert et al, 2012; Tanner et al, 2017) have been developed to isolate bacteria from positive blood culture samples for direct MALDI-TOF MS identification, allowing for significant reduction of the time to obtaining results, which is possible within only a few hours (Tian et al, 2016)
These reported techniques have some shortcomings such as the requirement of sophisticated equipment, high costs, and relatively low identification accuracy (Morgenthaler and Kostrzewa, 2015; Lin et al, 2017). Most of these studies have mainly focused on direct bacterial identification, and there is limited research on methods for the direct determination of the antibiotic susceptibility profiles of the infectious agents identified in positive blood cultures (Romero-Gómez et al, 2012; Croxatto et al, 2014; Barnini et al, 2016; Tian et al, 2016; Bazzi et al, 2017), which is arguably more important for determining appropriate antibiotic treatment than organism identification
Summary
Bloodstream infection is one of the leading causes of death worldwide (Adhikari et al, 2010; Morgenthaler and Kostrzewa, 2015). New serum separator tubes (Moussaoui et al, 2010; Stevenson et al, 2010; Wimmer et al, 2012), detergent reagents (Ferroni et al, 2010; Yonetani et al, 2012; Morgenthaler and Kostrzewa, 2015), centrifugation conditions, filters (Fothergill et al, 2013), and commercial kits (La Scola and Raoult, 2009; Juiz et al, 2012; Saffert et al, 2012; Tanner et al, 2017) have been developed to isolate bacteria from positive blood culture samples for direct MALDI-TOF MS identification, allowing for significant reduction of the time to obtaining results, which is possible within only a few hours (Tian et al, 2016) These reported techniques have some shortcomings such as the requirement of sophisticated equipment, high costs, and relatively low identification accuracy (Morgenthaler and Kostrzewa, 2015; Lin et al, 2017). Most of these studies have mainly focused on direct bacterial identification, and there is limited research on methods for the direct determination of the antibiotic susceptibility profiles of the infectious agents identified in positive blood cultures (Romero-Gómez et al, 2012; Croxatto et al, 2014; Barnini et al, 2016; Tian et al, 2016; Bazzi et al, 2017), which is arguably more important for determining appropriate antibiotic treatment than organism identification
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