M Ballestero-Téllez1, F Docobo-Pérez2, J M Rodríguez-Martínez3, M C Conejo4, M S Ramos-Guelfo5, J Blázquez6, J Rodríguez-Baño7, A Pascual8. 1. Unidad intercentros de Enfermedades Infecciosas, Microbiología y Medicina Preventiva, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain. 2. Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain; Departmento de Microbiología, Universidad de Sevilla, Seville, Spain; Red Española de Investigación en Patología Infecciosa (REIPI), Instituto de Salud Carlos III, Madrid, Spain. Electronic address: fdocobop@yahoo.es. 3. Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain; Departmento de Microbiología, Universidad de Sevilla, Seville, Spain; Red Española de Investigación en Patología Infecciosa (REIPI), Instituto de Salud Carlos III, Madrid, Spain. 4. Departmento de Microbiología, Universidad de Sevilla, Seville, Spain. 5. Unidad intercentros de Enfermedades Infecciosas, Microbiología y Medicina Preventiva, Hospital Universitario Virgen Macarena, Seville, Spain. 6. Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain; Red Española de Investigación en Patología Infecciosa (REIPI), Instituto de Salud Carlos III, Madrid, Spain. 7. Unidad intercentros de Enfermedades Infecciosas, Microbiología y Medicina Preventiva, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain; Red Española de Investigación en Patología Infecciosa (REIPI), Instituto de Salud Carlos III, Madrid, Spain; Departmento de Medicina, Universidad de Sevilla, Seville, Spain. 8. Unidad intercentros de Enfermedades Infecciosas, Microbiología y Medicina Preventiva, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Seville, Spain; Departmento de Microbiología, Universidad de Sevilla, Seville, Spain; Red Española de Investigación en Patología Infecciosa (REIPI), Instituto de Salud Carlos III, Madrid, Spain.
Abstract
OBJECTIVES: Fosfomycin is re-evaluated as a treatment of multidrug-resistant Enterobacteriaceae infections. However, MIC differences have been described among the different susceptibility testing. The aim was to study the role of the different inoculum size used in agar dilution with respect to broth microdilution, according to CLSI, in the fosfomycin MIC discrepancies. METHODS: Fosfomycin MICs were determined using agar dilution (reference) and broth microdilution in 220 Escherichia coli (n=81) and Klebsiella pneumoniae (n=139) clinical isolates. Fosfomycin mutant frequencies were determined in 21 E. coli (MIC=1mg/L) and 21 K. pneumoniae (MIC=16mg/L). The emergence of resistant subpopulations of five E. coli strains (MIC=1mg/L) was monitored over the time by microdilution assay using 0, 4 and 8 mg/L of fosfomycin, and eight different inocula (5×105-3.91×103 CFU/well, 1 : 2 dilutions). RESULTS: For E. coli, 86.4% of categorical agreement (CA), 9.1% very major errors (VME), 3.3% major errors (ME) and 9.9% minor errors (mE) were found. For K. pneumoniae, CA was 51.1%, VME 15.7%, ME 28.4% and mE 25.2%. Essential agreement (±1-log2) was observed in 55.45%. By microdilution, 35.9% of the MICs showed discrepancies of ≥2 dilutions. Initial inoculum used was 5.63 times higher in the microdilution method, in range with CLSI methodology for both techniques. Fosfomycin mutant frequencies were 6.05×10-5 (4×MIC) to 5.59×10-7 (256×MIC) for E. coli, and 1.49×10-4 (4×MIC) to 1.58×10-5 (16×MIC) for K. pneumoniae. Resistant subpopulations arose mainly after 8 h of incubation with inocula >3.13×104 CFU/well. CONCLUSIONS: The higher inoculum used in the microdilution method enriched the initial inoculum with resistant subpopulations and could partially explain the fosfomycin MIC discrepancies with respect to the agar dilution method.
OBJECTIVES:Fosfomycin is re-evaluated as a treatment of multidrug-resistant Enterobacteriaceae infections. However, MIC differences have been described among the different susceptibility testing. The aim was to study the role of the different inoculum size used in agar dilution with respect to broth microdilution, according to CLSI, in the fosfomycin MIC discrepancies. METHODS:Fosfomycin MICs were determined using agar dilution (reference) and broth microdilution in 220 Escherichia coli (n=81) and Klebsiella pneumoniae (n=139) clinical isolates. Fosfomycin mutant frequencies were determined in 21 E. coli (MIC=1mg/L) and 21 K. pneumoniae (MIC=16mg/L). The emergence of resistant subpopulations of five E. coli strains (MIC=1mg/L) was monitored over the time by microdilution assay using 0, 4 and 8 mg/L of fosfomycin, and eight different inocula (5×105-3.91×103 CFU/well, 1 : 2 dilutions). RESULTS: For E. coli, 86.4% of categorical agreement (CA), 9.1% very major errors (VME), 3.3% major errors (ME) and 9.9% minor errors (mE) were found. For K. pneumoniae, CA was 51.1%, VME 15.7%, ME 28.4% and mE 25.2%. Essential agreement (±1-log2) was observed in 55.45%. By microdilution, 35.9% of the MICs showed discrepancies of ≥2 dilutions. Initial inoculum used was 5.63 times higher in the microdilution method, in range with CLSI methodology for both techniques. Fosfomycin mutant frequencies were 6.05×10-5 (4×MIC) to 5.59×10-7 (256×MIC) for E. coli, and 1.49×10-4 (4×MIC) to 1.58×10-5 (16×MIC) for K. pneumoniae. Resistant subpopulations arose mainly after 8 h of incubation with inocula >3.13×104 CFU/well. CONCLUSIONS: The higher inoculum used in the microdilution method enriched the initial inoculum with resistant subpopulations and could partially explain the fosfomycin MIC discrepancies with respect to the agar dilution method.
Authors: Robert K Flamm; Paul R Rhomberg; Jill M Lindley; Kim Sweeney; E J Ellis-Grosse; Dee Shortridge Journal: Antimicrob Agents Chemother Date: 2019-04-25 Impact factor: 5.191
Authors: Iain J Abbott; Elke van Gorp; Aart van der Meijden; Rixt A Wijma; Joseph Meletiadis; Jason A Roberts; Johan W Mouton; Anton Y Peleg Journal: Antimicrob Agents Chemother Date: 2020-05-21 Impact factor: 5.191
Authors: Aaron E Lucas; Ryota Ito; Mustapha M Mustapha; Christi L McElheny; Roberta T Mettus; Sarah L Bowler; Serena F Kantz; Marissa P Pacey; A William Pasculle; Vaughn S Cooper; Yohei Doi Journal: J Clin Microbiol Date: 2017-12-26 Impact factor: 5.948
Authors: Iain J Abbott; Elke van Gorp; Rixt A Wijma; Joseph Meletiadis; Jason A Roberts; Johan W Mouton; Anton Y Peleg Journal: Antimicrob Agents Chemother Date: 2020-02-21 Impact factor: 5.191