Floriana Campanile1, Mandy Wootton2, Leanne Davies2, Ausilia Aprile3, Alessia Mirabile3, Stefano Pomponio4, Federica Demetrio4, Dafne Bongiorno3, Timothy R Walsh5, Stefania Stefani3, Maria Lina Mezzatesta3. 1. Department of Biomedical and Biotechnological Sciences, section of Microbiology, University of Catania, Italy. Electronic address: f.campanile@unict.it. 2. Specialist Antimicrobial Chemotherapy Unit, Public Health Wales, University Hospital of Wales, Cardiff, United Kingdom. 3. Department of Biomedical and Biotechnological Sciences, section of Microbiology, University of Catania, Italy. 4. Scientific division, Liofilchem S.r.l. Roseto degli Abruzzi (TE), Italy. 5. Department of Zoology, University of Oxford, United Kingdom.
Abstract
OBJECTIVES: Many clinical laboratories have difficulty in routinely performing in vitro fosfomycin susceptibility testing using the agar dilution (AD) method, considered to be the gold standard method. The objective of our work was to evaluate a rapid commercial fosfomycin agar dilution panel against clinical Staphylococcus aureus and Enterobacterales strains, in two different centres located in Italy and in the UK. METHODS: A total of 99 Enterobacterales (mostly Escherichia coli and Klebsiella pneumoniae) and 80 S. aureus clinical isolates was used to evaluate the commercial device, a 12-well panel containing fosfomycin incorporated into CA-MH agar supplemented with 25mg/L of glucose-6-phosphate (Liofilchem S.r.l., Roseto degli Abruzzi, Italy). Testing was performed in two centres (Italy and UK) and kit results were compared against the gold standard in-house AD MIC method. RESULTS: According to the EUCAST breakpoints, fosfomycin inhibited 61% of the S. aureus strains, and 76% of the Enterobacterales isolates tested by the AD reference method. There was a Categorical Agreement (CA) of 100% and an Essential Agreement (EA) of 91.25% for S. aureus; while the Enterobacterales strains showed a CA of 94% and an EA of 97%. No evaluation errors were observed among S. aureus, while 5% Major Error and 1% Very Major Error were observed for the Enterobacterales. CONCLUSIONS: Our results confirmed the feasibility of determining fosfomycin susceptibility using a commercial AD panel as a routine substitution for the AD test. The few differences observed were only in strains with MICs around the breakpoint used.
OBJECTIVES: Many clinical laboratories have difficulty in routinely performing in vitro fosfomycin susceptibility testing using the agar dilution (AD) method, considered to be the gold standard method. The objective of our work was to evaluate a rapid commercial fosfomycinagar dilution panel against clinical Staphylococcus aureus and Enterobacterales strains, in two different centres located in Italy and in the UK. METHODS: A total of 99 Enterobacterales (mostly Escherichia coli and Klebsiella pneumoniae) and 80 S. aureus clinical isolates was used to evaluate the commercial device, a 12-well panel containing fosfomycin incorporated into CA-MH agar supplemented with 25mg/L of glucose-6-phosphate (Liofilchem S.r.l., Roseto degli Abruzzi, Italy). Testing was performed in two centres (Italy and UK) and kit results were compared against the gold standard in-house AD MIC method. RESULTS: According to the EUCAST breakpoints, fosfomycin inhibited 61% of the S. aureus strains, and 76% of the Enterobacterales isolates tested by the AD reference method. There was a Categorical Agreement (CA) of 100% and an Essential Agreement (EA) of 91.25% for S. aureus; while the Enterobacterales strains showed a CA of 94% and an EA of 97%. No evaluation errors were observed among S. aureus, while 5% Major Error and 1% Very Major Error were observed for the Enterobacterales. CONCLUSIONS: Our results confirmed the feasibility of determining fosfomycin susceptibility using a commercial AD panel as a routine substitution for the AD test. The few differences observed were only in strains with MICs around the breakpoint used.