695. Activity of Imipenem–Relebactam and Ceftolozane–Tazobactam Against a Contemporary Collection of Gram-Negative Bacteria from New York City

Background Carbapenem-resistant Gram-negative bacteria are important nosocomial pathogens, and therapeutic options are often limited. Methods Clinical isolates were gathered during a surveillance study in 2017 involving 7 hospitals in Brooklyn, NY. Isolates underwent susceptibility testing using the agar dilution method; for the combination of imipenem-relebactam and ceftolozane-tazobactam, the concentrations of relebactam and tazobactam were fixed at 4 µg/mL. Breakpoints were defined according to CLSI criteria; for imipenem-relebactam, the breakpoint of imipenem was utilized. Isolates were screened by PCR for common carbapenemases. Results Overall susceptibility patterns are given in the Table. Of 1805 isolates of E. coli (including 4 with blaKPC), 100% were susceptible to imipenem and imipenem-relebactam. Of 503 isolates of K. pneumoniae (including 19 isolates with blaKPC), all were susceptible to imipenem-relebactam. Of 171 isolates of Enterobacter spp. (including 3 with blaKPC), 100% were susceptible to imipenem-relebactam. Of 260 isolates of P. aeruginosa, 96% were susceptible to imipenem-relebactam and nearly all to ceftolozane-tazobactam. Against A. baumannii, the activity of imipenem-relebactam was the same as imipenem and the ceftolozane-tazobactam MIC was ≤ 4 µg/mL in 65% of isolates. Conclusion Imipenem-relebactam possesses promising activity against multidrug-resistant Enterobacteriaceae endemic to New York City. Ceftolozane-tazobactam demonstrated excellent activity against P. aeruginosa, including isolates resistant to carbapenems. Disclosures All authors: No reported disclosures.