Performance evaluation of Bruker UMIC® microdilution panel and disc diffusion to determine cefiderocol susceptibility in Enterobacterales, <italic>Acinetobacter baumannii</italic>, <italic>Pseudomonas aeruginosa</italic>, <italic>Stenotrophomonas maltophilia</italic>, <italic>Achromobacter xylosoxidans</italic> and <italic>Burkolderia species</italic>.

Purpose: Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (<italic>n</italic> = 4, 4.2%) and MEs (<italic>n</italic> = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); <italic>P. aeruginosa</italic> (19/19); <italic>A. xylosoxidans</italic> (5/6); <italic>S. maltophilia</italic> (5/6); <italic>Burkholderia</italic> spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, <italic>P. aeuroginosa</italic>, <italic>A. baumannii</italic> and <italic>S. maltophilia</italic>. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and <italic>P. aeruginosa</italic> (16/40, 40%). Disc diffusion showed a poor performance in <italic>A. xylosoxidans</italic> and <italic>Burkholderia</italic> spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of <italic>P. aeruginosa</italic>-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories.Methods: Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (<italic>n</italic> = 4, 4.2%) and MEs (<italic>n</italic> = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); <italic>P. aeruginosa</italic> (19/19); <italic>A. xylosoxidans</italic> (5/6); <italic>S. maltophilia</italic> (5/6); <italic>Burkholderia</italic> spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, <italic>P. aeuroginosa</italic>, <italic>A. baumannii</italic> and <italic>S. maltophilia</italic>. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and <italic>P. aeruginosa</italic> (16/40, 40%). Disc diffusion showed a poor performance in <italic>A. xylosoxidans</italic> and <italic>Burkholderia</italic> spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of <italic>P. aeruginosa</italic>-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories.Results: Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (<italic>n</italic> = 4, 4.2%) and MEs (<italic>n</italic> = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); <italic>P. aeruginosa</italic> (19/19); <italic>A. xylosoxidans</italic> (5/6); <italic>S. maltophilia</italic> (5/6); <italic>Burkholderia</italic> spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, <italic>P. aeuroginosa</italic>, <italic>A. baumannii</italic> and <italic>S. maltophilia</italic>. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and <italic>P. aeruginosa</italic> (16/40, 40%). Disc diffusion showed a poor performance in <italic>A. xylosoxidans</italic> and <italic>Burkholderia</italic> spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of <italic>P. aeruginosa</italic>-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories.Conclusion: Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (<italic>n</italic> = 4, 4.2%) and MEs (<italic>n</italic> = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); <italic>P. aeruginosa</italic> (19/19); <italic>A. xylosoxidans</italic> (5/6); <italic>S. maltophilia</italic> (5/6); <italic>Burkholderia</italic> spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, <italic>P. aeuroginosa</italic>, <italic>A. baumannii</italic> and <italic>S. maltophilia</italic>. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and <italic>P. aeruginosa</italic> (16/40, 40%). Disc diffusion showed a poor performance in <italic>A. xylosoxidans</italic> and <italic>Burkholderia</italic> spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of <italic>P. aeruginosa</italic>-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories. [ABSTRACT FROM AUTHOR]