Etest versus broth microdilution for ceftaroline MIC determination with Staphylococcus aureus: Results from PREMIUM, a European multicentre study (2017)

Type of publication:
Journal article

Canton R.; Morosini M.I.; Livermore D.M.; Diaz-Reganon J.; Rossolini G.M.; Verhaegen J.; Cartuyvels R.; Claeys G.; De Beenhouwer H.; Delmee M.; Denis O.; Glupczynski Y.; Leven G.; Melin P.; Pierard D.; Pagani L.; Arena F.; Luzzaro F.; Gesu G.P.; Serra R.; D'Argenio A.; Sarti M.; Pecile P.; Mazzariol A.; Biscaro V.; Manso E.; Catania M.R.; Giraldi C.; Stefani S.; Labonia M.; Aschbacher R.; Giammanco A.; Cristino M.; Sancho L.; Diogo J.M.; Ramalheira E.; Ramos H.; Pinheiro D.; Garcia-Castillo M.; Calvo J.; Oliver A.; Gimeno C.; Pascual A.; Quintano F.T.; Bartolome R.; Cisterna R.; Cercenado E.; Merino P.; Marco F.; Bou G.; Sanchez J.E.G.; Cilla G.; Iglesias M.R.; Droz S.; Frei R.; James D.; Mushtaq S.; Howe R.; Paton R.; Gould K.; Eyre A.; Jepson A.; Swann A.; Weston D.; *Harvey G.; Humphrey H.

Journal of Antimicrobial Chemotherapy; 2017; vol. 72 (no. 2); p. 431-436

Objectives: To compare the concordance of ceftaroline MIC values by reference broth microdilution (BMD) and Etest (bioMerieux, France) for MSSA and MRSA isolates obtained from PREMIUM (D372SL00001), a European multicentre study. Methods: Ceftaroline MICs were determined by reference BMD and by Etest for 1242 MSSA and MRSA isolates collected between February and May 2012 from adult patients with community-acquired pneumonia or complicated skin and soft tissue infections; tests were performed across six European laboratories. Selected isolates with ceftaroline resistance in broth (MIC >1 mg/L) were retested in three central laboratories to confirm their behaviour. Results: Overall concordance between BMD and Etest was good, with >97% essential agreement and >95% categorical agreement. Nevertheless, 12 of the 26 MRSA isolates found resistant by BMD scored as susceptible by Etest, with MICs <1 mg/L, thus counting as very major errors, whereas only 5 of 380 MRSA isolates found ceftaroline susceptible in BMD were miscategorized as resistant by Etest. Twenty-one of the 26 isolates with MICs of 2 mg/L by BMD were then retested twice by each of three central laboratories: BMD MICs of 2 mg/L were consistently found for 19 of the 21 isolates. Among 147 Etest results for these 21 isolates (original plus six repeats per isolate) 112 were >1 mg/L. Conclusions: BMD and Etest have good overall agreement for ceftaroline against Staphylococcus aureus; nevertheless, reliable Etest based discrimination of the minority of ceftaroline-resistant (MIC 2 mg/L) MRSA is extremely challenging, requiring careful reading of strips, ideally with duplicate testing.

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