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Background Delafloxacin is a new anionic fluoroquinolone with enhanced activity against methicillin-resistant S. aureus (MRSA). Delafloxacin has become a valuable option in the treatment of skin and soft-tissue infections. Methods Unique patient isolates of S. aureus were gathered during a surveillance study performed in 2017 involving 7 hospitals in Brooklyn, NY. Isolates underwent susceptibility testing using the agar dilution method; results were interpreted according to CLSI and FDA defined breakpoints. For select isolates, (1) multilocus sequence typing (MLST) was performed using established PCR primers and conditions, (2) mutations involving grlA, grlB, gyrA, and gyrB were identified by PCR, and (3) MICs for delafloxacin were performed with and without the addition of 32 µg/mL of the efflux inhibitor 1-(1-naphthyl methyl)-piperazine (NMP). Results During the surveillance study, a total of 757 isolates of S. aureus were gathered. Susceptibility results are given in the table. Fifteen delafloxacin-resistant isolates underwent MLST, and 14 were found to belong to ST105 and 1 to ST8. ST105 was recovered from all 7 hospitals. In contrast, of 14 delafloxacin-susceptible MRSA, identified ST clades included ST72 (n = 4), ST8 (n = 8), ST5 (n = 1), and ST1181 (n = 1). For 6 delafloxacin-resistant isolates, alterations in (1) GrlA included Ser80Tyr/Phe (5 isolates) and Glu84Gly (4 isolates) and (2) GyrA included Ser84 Leu (6 isolates), Glu88Lys (5 isolates) and Ser85Pro (1 isolate). The addition of the efflux inhibitor NMP did not affect delafloxacin MICs in the 5 isolates tested. Conclusion Clonal spread of delafloxacin-resistant isolates of MRSA has been identified in Brooklyn, NY. Alterations in GrlA and GyrA were identified in the delafloxacin-resistant isolates. Disclosures All authors: No reported disclosures. |
