Comparative evaluation of susceptibility testing methods for colistin and polymyxin B on isolates of Enterobacteriaceae / 中华检验医学杂志

ABSTRACT

Objective:To provide a promising and optimal laboratory susceptibility-testing method for the clinical usage of antibiotic (polymyxin), four susceptibility-testing methods were performed and the broth microdilution (BMD) was chosen as the gold standard.Methods:A total number of eighty-eight nonduplicate clinical Enterobacteriaceae specimes were collected from January to December of 2019 in the First Affiliated Hospital, Fujian Medical University. Among the clinical specimens, of which six strains were positive for mcr-1. The minimal inhibitory concentration (MIC) of polymyxin of the clinical specimens were examined by the following methods: (1) broth microdilution, (2) colistin broth disk elution, (3) Vitek-2?, (4)BD PhoenixTM,(5)commercial broth microdilution. With BMD as reference, essential agreement (EA), categorical agreement(CA), very major error(VME) and major error (ME) of polymyxins for different methods were analyzed. The Kappa-consistency testing, paired Chi-square testing and the Spearman-rank correlation testing were used to analyze the consistency between the four antimicrobial susceptibility testing methods and the gold standard.Results:Taking broth microdilution as reference, the EA of colistin broth disk elution, Vitek-2?, BD PhoenixTM, commercial broth microdilution were 94.32% (83/88), 92.05% (81/88), 90.90% (80/88), and 96.59%(85/88), respectively. The CA of all the four methods were 100% (88/88). No VME and ME were recorded for four methods. Moreover, the consistency between four susceptibility testing methods and the gold standard is acceptable (Kappa values=1, P<0.001, McNemar test P=1 and r>0.5, P<0.05). Conclusions:In the present work, four susceptibility testing methods all met the standards recommended jointly by the Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing, of which the performance of the commercial broth microdilution and CBDE fared relatively well. Thus, these four methods could be routinely used in clinical microbiology laboratory of our hospital for colistin and polymyxin B susceptibility testing.