2059. Comparative Evaluation of Ceftaroline Susceptibility Methods in Clinical Isolates of Methicillin-Resistant Staphylococcus aureus (MRSA): Results from a Multicenter Study

BACKGROUND: Ceftaroline (CPT) is a last generation cephalosporin with activity against MRSA. Recent data raised concerns regarding routine susceptibility testing in clinical laboratories, suggesting a poor performance for detecting nonsusceptible S. aureus (MIC >1 µg/dL) using either disc or gradient strips (Cantón R 2017) AIM: To evaluate the results of CPT susceptibility testing with Etest(®) and disk diffusion (Kirby–Bauer technique [KB]) as compared with broth microdilution (BMD), in clinical isolates of MRSA obtained from different hospitals in Santiago, Chile. METHODS: During 2017, we prospectively collected consecutive clinical strains of MRSA recovered from the blood or other sterile sites in ten tertiary-care hospitals in Santiago, Chile. One isolate per patient was obtained. Identification was confirmed by MALDI-TOF and susceptibility testing of all isolates was performed at a central lab. CPT susceptibility was evaluated by BMD and KB following CLSI 2017 directions. Etest was performed as per manufacturer’s instructions. Categorical agreement (CA), essential agreement (EA) and very major errors (VME) were evaluated. Susceptibilities were analyzed using CLSI established breakpoints RESULTS: Forty unique MRSA isolates were tested. Using BMD, the MIC(50)/MIC(90) was 2/4 μg/dL, respectively. Moreover, only 18 (45%) isolates were CPT susceptible. Out of the remaining 22 MRSA strains, 8 (20%) were intermediate and 14 (35%) CPT-resistant (CPT-R). Using Etest, the MIC(50)/MIC(90) was 1/2 μg/dL, with 31 (78%) isolates being considered susceptible and the remaining catalogued as intermediate. CPT susceptibility using KB catalogued 38 (95%) isolates as susceptible and only 2 as intermediate. No CPT-R strains were found by Etest or KB. The CA was for Etest and KB, respectively; Etest’s EA was 80%. Worryingly, out of 14 CPT-R isolates by BMD, 6 were deemed susceptible by Etest and 12 by KB, obtaining VME rates of 43 and 87%, respectively CONCLUSION: Performance of both Etest and KB to assess CPT susceptibility in MRSA isolates from Chile was poor, with a unacceptably high proportion of VME, and a CA lower than 50% for both techniques. Correlation of CPT susceptibility with the molecular epidemiology of the isolates is currently being performed DISCLOSURES: All authors: No reported disclosures.