Article Figures & Data
Figures
- FIG 1
Cefazolin (left) and ceftriaxone (right) MIC distributions for Escherichia coli (https://mic.eucast.org/Eucast2/SearchController/search.jsp?action=performSearch&BeginIndex=0&Micdif=mic&NumberIndex=50&Antib=-1&Specium=162). Categorical agreement rates are expected to be lower for cefazolin, because the breakpoints bisect the wild-type MIC distribution. S, susceptible; I, intermediate; R, resistant.
Tables
- TABLE 1
Variables to be detailed in Materials and Methods for CLSI BMD reference method
Parametera M07 standard Data to be documented in study publication Test medium for nonfastidious bacteria CA-MHB manufactured according to ISO technical standard 16782:2016 (18) Brand of CA-MHB Method for cation adjustment Any special requirements for handling CA-MHB for specific antimicrobial agents Test medium for fastidious bacteria As stipulated by M100 standard (6) or M45 guideline Brand of alternative medium Sources and concentrations of supplements Any special requirements for handling alternative media for specific antimicrobial agents Antimicrobial stock solutions Antimicrobial powder formulation designed for AST, obtained from drug manufacturer, USP, or other appropriate commercial sources; pharmacy-grade parenteral formulations should not be used Source of antimicrobial powder and solvent and diluent used to make stock solutions BMD panel preparation Dilution of stock solution and dispensing of 0.05 or 0.1 ml/well using pipette or dispensing device Method for preparation of panels (individual or batch), volume per well, and storage conditions Range of concentrations tested Number of lot numbers of panels used in study Inoculum suspension preparation and panel inoculation Direct colony suspension method or growth method to achieve 0.5 McFarland standard Inoculum suspension preparation and standardization method Dilution and inoculation of wells with pipette or inoculator device (final target of 5 × 105 CFU/ml) Method for preparation of intermediate dilutions (diluent and volumes) Purity plate prepared (advised) (ahWG consensus is to prepare for each isolate)
Colony counts performed periodicallyMethod and volume for panel inoculation
Method of purity plate preparationTargeted final organism concentration in wells Procedure, acceptable range, and indications for colony counts Indication of whether same inoculum is used for both BMD and cAST Incubation procedure Precautions taken to maintain consistent incubation temperatures and to prevent drying of panels Incubation parameters Temperature, atmosphere, and time varying by species (consult M07) Reading of endpoints Complete inhibition of growth measured with naked eye (see exceptions to complete inhibition in M07b) (ahWG recommends ≥2 independent readers to determine MICs for each panel) Viewing device used to facilitate reading Number of independent readers Observation of any “equivocal” endpoints and how they were read (e.g., trailing) (obtaining photographs to illustrate any unique reading recommendations, if possible) Mechanism used to arbitrate discrepant MICs between readers QC At minimum, following M07 QC recommendations CLSI-recommended QC strains used Any additional QC strains used and rationale for strain selection ↵a CA-MHB, cation-adjusted Mueller-Hinton broth; ISO, International Organization for Standardization; USP, U.S. Pharmacopeia; BMD, broth microdilution; cAST, commercial antimicrobial susceptibility test; ahWG, ad hoc working group; CLSI, Clinical and Laboratory Standards Institute; QC, quality control.
↵b Exceptions include the evaluation of trimethoprim-sulfamethoxazole, where 80% growth inhibition is read as the endpoint.
- TABLE 2
Variables to be detailed in Materials and Methods for the cAST under evaluation
Parametera Testing considerations Data to be documented in study publication (if applicable) Regulatory status of cAST cASTs that have not undergone regulatory approval may not be optimized Regulatory status of cAST (RUO, IUO, or IVD) Version/edition of cAST hardware/software Newer approved versions/editions are often designed to enhance performance Version/edition of hardware/software Range of antimicrobial agent concentrations tested Some concentration ranges may differ from those in BMD panels Range of concentrations tested and description of how MICs are evaluated if concentrations in cAST panel differ from those in BMD panel Lot numbers Performance variability among lot numbers of cAST panels or gradient diffusion strips may be encountered Number of lot numbers evaluated Inoculum suspension preparation and panel inoculation Single inoculum for reference BMD and cAST? Indication of whether same inoculum was used for both BMD and cAST QC Acceptable ranges for CLSI QC strains for cASTs may be slightly different from those published in M100 Manufacturer's QC instructions followed precisely ↵a cAST, commercial antimicrobial susceptibility test; RUO, research use only; IUO, investigational use only; IVD, in vitro diagnostic; QC, quality control.
- TABLE 3
Additional variables to be detailed when cAST method is gradient strip or disk diffusion method
Parametera Testing considerations Data to be documented in study publication (if applicable) MHA or supplemented MHA Performance may vary across brands and lot numbers of MHA Brand of MHA Disks and gradient strips are typically developed with a single brand of MHA Number of lot numbers evaluated Troubleshooting of MHA source if performance issues are noted (determining whether brand used is different from that used by gradient strip manufacturer) Method used to determine MIC endpoints and management of colonies within zone Some use a magnifying glass or digital camera/software for endpoint measurement Method used to determine MIC endpoints, including managing any colonies within zone or equivocal endpoints MIC values may differ depending on how colonies in the zone of growth inhibition are evaluated Any procedure for rounding between 2-fold dilutions Interpretation of endpoints may be challenging; follow manufacturer's instructions precisely (obtain photographs for guidance, if possible) ↵a MHA, Mueller-Hinton agar.
Supplemental material
- Supplemental file 1 -
Tables S1 (Calculation of method comparison agreement and error categories and acceptable criteria), S2 (Acceptance performance rates for cASTs, by the error rate bound method, for antimicrobials with an intermediate category), S3 (Acceptance performance rates for ASTs, by the error rate bound method, when no intermediate category exists), and S4 (Hypothetical examples of arbitrating discrepancies between cAST and BMD)
PDF, 304K
- Supplemental file 1 -
