Barnini Simona, Brucculeri Veronica, Morici Paola, Ghelardi Emilia, Florio Walter, Lupetti Antonella
Azienda Ospedaliero-Universitaria Pisana, Pisa, Italy.
Dipartimento di Ricerca Traslazionale e delle Nuove Tecnologie in Medicina e Chirurgia, Università di Pisa, Pisa, Italy.
BMC Microbiol. 2016 Aug 12;16(1):185. doi: 10.1186/s12866-016-0805-5.
Rapid identification and antimicrobial susceptibility testing (AST) of the causative agent(s) of bloodstream infections can lead to prompt appropriate antimicrobial therapy. To shorten species identification, in this study bacteria were recovered from monomicrobial blood cultures by serum separator tubes and spotted onto the target plate for direct MALDI-TOF MS identification. Proper antibiotics were selected for direct AST based on species identification. In order to obtain rapid AST results, bacteria were recovered from positive blood cultures by two different protocols: by serum separator tubes (further referred to as PR1), or after a short-term subculture in liquid medium (further referred to as PR2). The results were compared with those obtained by the method currently used in our laboratory consisting in identification by MALDI-TOF and AST by Vitek 2 or Sensititre on isolated colonies.
The direct MALDI-TOF method concordantly identified with the current method 97.5 % of the Gram-negative bacteria and 96.1 % of the Gram-positive cocci contained in monomicrobial blood cultures. The direct AST by PR1 and PR2 for all isolate/antimicrobial agent combinations was concordant/correct with the current method for 87.8 and 90.5 % of Gram-negative bacteria and for 93.1 and 93.8 % of Gram-positive cocci, respectively. In particular, 100 % categorical agreement was found with levofloxacin for Enterobacteriaceae by both PR1 and PR2, and 99.0 and 100 % categorical agreement was observed with linezolid for Gram-positive cocci by PR1 and PR2, respectively. There was no significant difference in accuracy between PR1 and PR2 for Gram-negative bacteria and Gram-positive cocci.
This newly described method seems promising for providing accurate AST results. Most importantly, these results would be available in a few hours from blood culture positivity, which would help clinicians to promptly confirm or streamline an effective antibiotic therapy in patients with bloodstream infections.
血流感染病原体的快速鉴定和抗菌药物敏感性试验（AST）可实现及时、恰当的抗菌治疗。为缩短菌种鉴定时间，本研究采用血清分离管从单一微生物血培养物中分离细菌，并点种到靶板上进行直接基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）鉴定。根据菌种鉴定结果选择合适的抗生素进行直接AST。为获得快速AST结果，通过两种不同方案从阳性血培养物中分离细菌：采用血清分离管（以下简称PR1），或在液体培养基中短期传代培养后（以下简称PR2）。将结果与我们实验室目前使用的方法进行比较，该方法包括通过MALDI-TOF进行鉴定以及通过Vitek 2或Sensititre对分离菌落进行AST。
直接MALDI-TOF方法与当前方法对单一微生物血培养物中97.5%的革兰阴性菌和96.1%的革兰阳性球菌鉴定结果一致。PR1和PR2对所有分离菌/抗菌药物组合的直接AST与当前方法对革兰阴性菌的一致性/正确率分别为87.8%和90.5%，对革兰阳性球菌的一致性/正确率分别为93.1%和93.8%。特别是，PR1和PR2对肠杆菌科细菌的左氧氟沙星鉴定结果均为100%完全一致，PR1和PR2对革兰阳性球菌的利奈唑胺鉴定结果分别为99.0%和100%完全一致。对于革兰阴性菌和革兰阳性球菌，PR1和PR2在准确性上无显著差异。
这种新描述的方法似乎有望提供准确的AST结果。最重要的是，从血培养阳性起数小时内即可获得这些结果，这将有助于临床医生迅速确认或简化血流感染患者的有效抗生素治疗方案。
