Infection and Drug Resistance (Apr 2022)
Direct Identification, Antimicrobial Susceptibility Testing, and Extended-Spectrum β-Lactamase and Carbapenemase Detection in Gram-Negative Bacteria Isolated from Blood Cultures
Abstract
Hainan Wen,1 Shoujun Xie,2 Yueyi Liang,2 Yanchao Liu,2 Honglian Wei,1 Qian Sun,1 Weigang Wang,1,3 Baojiang Wen,1,3 Jianhong Zhao1,3 1The Second Hospital of Hebei Medical University, Shijiazhuang, Hebei, People’s Republic of China; 2Clinical Laboratory, the Affiliated Hospital of Chengde Medical University, Chengde, Hebei, People’s Republic of China; 3Hebei Provincial Center for Clinical Laboratories, Shijiazhuang, Hebei, People’s Republic of ChinaCorrespondence: Jianhong Zhao, The Second Hospital of Hebei Medical University, 215 West Heping Road, Shijiazhuang, Hebei Province, 050051, People’s Republic of China, Tel +86 158 03210790, Fax +86 311 66002851, Email [email protected]: To shorten the turnaround time for blood culture (BC) analyses, a rapid method was developed for the direct identification, antimicrobial susceptibility testing (AST), and multidrug resistance testing of bacteria-positive BCs.Materials and Methods: The mixtures in BC bottles were treated with the multistep centrifugation method developed here and the conventional culture-based method. The bacterial sediment obtained after centrifugation was analyzed directly with MALDI-TOF MS and Vitek 2 Compact, and AST was performed directly with the Kirby–Bauer (K–B) disk diffusion, VITEK 2 Compact, and E-test methods. Extended spectrum lactamases (ESBLs) were detected with discs containing cefotaxime, cefotaxime/clavulanate, ceftazidime, and ceftazidime/clavulanate, and carbapenemase was detected with the modified carbapenem inactivation method (mCIM) and EDTA-mCIM (eCIM).Results: All the results of direct testing were compared to those of the conventional methods, to evaluate the accuracy of the direct methods. The accuracies of the direct Vitek 2 Compact and MALDI-TOF MS methods were 95.5% (214/224) and 90.2% (202/224), respectively. Direct AST with K–B, Vitek 2, and E-test showed category agreement of 96.0% (2611/2721), 96.1% (2614/2721), and 97.4% (2650/2721), respectively, and the major errors and very major errors were < 2% for all three methods. In the direct determination of ESBLs, the results for cefotaxime combined with cefotaxime/clavulanate were completely consistent with those after the standard isolation method. The carbapenemase detection rate with direct mCIM and eCIM was exactly the same as that with the standard method.Conclusion: These direct procedures based on multistep centrifugation are not only highly accurate but are appropriate for clinical laboratory use because the turnaround time is shorter.Keywords: blood culture, direct identification, direct antimicrobial susceptibility testing, extended-spectrum β-lactamase, carbapenemase, multistep centrifugation
