TY - JOUR
T1 - Two-site evaluation of the colistin broth disk elution test to determine colistin in vitro activity against Gram-negative bacilli
AU - Simner, Patricia J.
AU - Bergman, Yehudit
AU - Trejo, Marisol
AU - Roberts, Ava A.
AU - Marayan, Remy
AU - Tekle, Tsigereda
AU - Campeau, Shelley
AU - Kazmi, Abida Q.
AU - Bell, Drew T.
AU - Lewis, Shawna
AU - Tamma, Pranita D.
AU - Humphries, Romney
AU - Hindlerb, Janet A.
N1 - Publisher Copyright:
Copyright © 2019 American Society for Microbiology. All Rights Reserved.
PY - 2019/2
Y1 - 2019/2
N2 - Limited methods for colistin MIC determination are available to clinical microbiology laboratories. The purpose of this study was to evaluate the accuracy of the colistin broth disk elution (CBDE) test compared to that of broth microdilution (BMD) for identifying colistin MICs. CBDE was compared to colistin BMD using a collection of Gram-negative bacilli tested at two U.S. microbiology laboratories. The isolates tested included 121 retrospective clinical isolates, 45 prospective clinical isolates, and 6 mcr-1-positive Escherichia coli isolates. CBDE was performed with four 10-ml cation-adjusted Mueller-Hinton broth tubes per isolate, to which 0, 1, 2, and 4 colistin 10-μg disks were added, generating final concentrations in the tubes of 0 (growth control), 1, 2, and 4 μg/ml, respectively. MICs were evaluated visually and interpreted using Clinical and Laboratory Standards Institute breakpoints. Site 2 also compared CBDE to the reference broth macrodilution (BMAD) method (n = 110 isolates). Overall, CBDE yielded a categorical agreement (CA) and essential agreement (EA) of 98% and 99%, respectively, compared to the results of colistin BMD. Very major errors occurred for mcr-1-producing strains, with MICs fluctuating from 2 to 4 μg/ml on repeat testing. The results for all other isolates were in CA with those of BMD. CBDE versus BMAD had an EA of 100% and a CA of 100%. Compared to currently used techniques, CBDE is an easy and practical method to perform colistin MIC testing. Some mcr-1-producing isolates yielded MICs of 2 μg/ml by CBDE and 4 μg/ml by BMD. As such, the results for isolates with colistin MICs of 2 μg/ml by CBDE should be confirmed by the reference BMD method, and isolates with MICs of & 2 μg/ml should be evaluated for the presence of mcr genes.
AB - Limited methods for colistin MIC determination are available to clinical microbiology laboratories. The purpose of this study was to evaluate the accuracy of the colistin broth disk elution (CBDE) test compared to that of broth microdilution (BMD) for identifying colistin MICs. CBDE was compared to colistin BMD using a collection of Gram-negative bacilli tested at two U.S. microbiology laboratories. The isolates tested included 121 retrospective clinical isolates, 45 prospective clinical isolates, and 6 mcr-1-positive Escherichia coli isolates. CBDE was performed with four 10-ml cation-adjusted Mueller-Hinton broth tubes per isolate, to which 0, 1, 2, and 4 colistin 10-μg disks were added, generating final concentrations in the tubes of 0 (growth control), 1, 2, and 4 μg/ml, respectively. MICs were evaluated visually and interpreted using Clinical and Laboratory Standards Institute breakpoints. Site 2 also compared CBDE to the reference broth macrodilution (BMAD) method (n = 110 isolates). Overall, CBDE yielded a categorical agreement (CA) and essential agreement (EA) of 98% and 99%, respectively, compared to the results of colistin BMD. Very major errors occurred for mcr-1-producing strains, with MICs fluctuating from 2 to 4 μg/ml on repeat testing. The results for all other isolates were in CA with those of BMD. CBDE versus BMAD had an EA of 100% and a CA of 100%. Compared to currently used techniques, CBDE is an easy and practical method to perform colistin MIC testing. Some mcr-1-producing isolates yielded MICs of 2 μg/ml by CBDE and 4 μg/ml by BMD. As such, the results for isolates with colistin MICs of 2 μg/ml by CBDE should be confirmed by the reference BMD method, and isolates with MICs of & 2 μg/ml should be evaluated for the presence of mcr genes.
KW - Antimicrobial susceptibility testing
KW - Colistin
KW - Colistin broth disk elution
KW - Method
UR - http://www.scopus.com/inward/record.url?scp=85060922990&partnerID=8YFLogxK
U2 - 10.1128/JCM.01163-18
DO - 10.1128/JCM.01163-18
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C2 - 30282791
AN - SCOPUS:85060922990
SN - 0095-1137
VL - 57
JO - Journal of Clinical Microbiology
JF - Journal of Clinical Microbiology
IS - 2
M1 - e01163
ER -