Multicenter Evaluation of Colistin Broth Disk Elution and Colistin Agar Test: a Report from the Clinical and Laboratory Standards Institute.
Romney M Humphries, Daniel A Green, Audrey N Schuetz, Yehudit Bergman, Shawna Lewis, Rebecca Yee, Stephania Stump, Mabel Lopez, Nenad Macesic, Anne-Catrin Uhlemann, Peggy Kohner, Nicolynn Cole, Patricia J Simner
Author Information
Romney M Humphries: Accelerate Diagnostics, Tucson Arizona, USA rhumphries@axdx.com.
Daniel A Green: Clinical Microbiology Laboratory, Department of Pathology & Cell Biology, Columbia University Irving Medical Center, New York, New York, USA.
Audrey N Schuetz: Division of Clinical Microbiology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA.
Yehudit Bergman: Division of Medical Microbiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Shawna Lewis: Division of Medical Microbiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Rebecca Yee: Division of Medical Microbiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Stephania Stump: Division of Infectious Diseases, Columbia University Irving Medical Center, New York, New York, USA.
Mabel Lopez: Clinical Microbiology Laboratory, Department of Pathology & Cell Biology, Columbia University Irving Medical Center, New York, New York, USA.
Nenad Macesic: Division of Infectious Diseases, Columbia University Irving Medical Center, New York, New York, USA.
Anne-Catrin Uhlemann: Division of Infectious Diseases, Columbia University Irving Medical Center, New York, New York, USA. ORCID
Peggy Kohner: Division of Clinical Microbiology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA.
Nicolynn Cole: Division of Clinical Microbiology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA.
Patricia J Simner: Division of Medical Microbiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Susceptibility testing of the polymyxins (colistin and polymyxin B) is challenging for clinical laboratories. The Clinical and Laboratory Standards Institute (CLSI) Antimicrobial Susceptibility Testing Subcommittee evaluated two methods to enable accurate testing of these agents. These methods were a colistin broth disk elution (CBDE) and a colistin agar test (CAT), the latter of which was evaluated using two inoculum volumes, 1 μl (CAT-1) and 10 μl (CAT-10). The methods were evaluated using a collection of 270 isolates of , 122 isolates, and 106 spp. isolates. Overall, 94.4% of CBDE results were in essential agreement and 97.9% in categorical agreement (CA) with reference broth microdilution MICs. Nine very major errors (VME; 3.2%) and 3 major errors (ME; 0.9%) were observed. With the CBDE, 98.6% CA was observed for (2.5% VME, 0% ME), 99.3% CA was observed for (0% VME, 0.7% ME), and 93.1% CA was observed for spp. (5.6% VME, 3.3% ME). Overall, CA was 94.9% with 6.8% VME using CAT-1 and improved to 98.3% with 3.9% VME using CAT-10. No ME were observed using either CAT-1 or CAT-10. Using the CAT-1/CAT-10, the CA observed was 99.4%/99.7% for (1%/0.5% VME), 98.7%/100% for (8.3%/0% VME), and 88.5%/92.3% for spp. (21.4%/14.3% VME). Based on these data, the CLSI antimicrobial susceptibility testing (AST) subcommittee endorsed the CBDE and CAT-10 methods for colistin testing of and .
