2175. In vitro Potency of Ceftolozane/Tazobactam and Other Antipseudomonal β-Lactams Against P. aeruginosa

BACKGROUND: Challenges due to multidrug resistant Gram-negative bacterial pathogens such as P. aeruginosa (PSA) are increasing globally. Suboptimal antimicrobial therapy of infections caused by PSA is associated with increased morbidity and mortality. As a result, antimicrobial susceptibility (%S) studies are pivotal to identifying trends in antimicrobial resistance that inform decisions regarding choice of antimicrobial therapy. This study assessed the in vitro potency of 7 antipseudomonal agents including ceftolozane/tazobactam against PSA collected from numerous sites across the United States. METHODS: Multiple U.S. hospitals provided nonduplicate respiratory and blood isolates of PSA for potency testing. MICs against PSA were determined using broth microdilution methods according to CLSI for seven antimicrobials with antipseudomonal activity: aztreonam, cefepime, ceftazidime, ceftolozane/tazobactam, imipenem, meropenem and piperacillin/tazobactam. Susceptibility (%S) was defined per CLSI or FDA breakpoint criteria. RESULTS: Fourteen hospitals geographically spread across the United States provided total of 560 PSA isolates. Of the antibiotics assessed, %S to C/T was the highest at 95% with an MIC(50) of 1 µg/mL and MIC(90) of 2 µg/mL. In comparison, other %S (MIC(50)/MIC(90)) were as follows: ceftazidime 76% (4/64); cefepime 75% (4/32); piperacillin/tazobactam 73% (8/128), meropenem 72% (0.5/16); aztreonam 65% (8/32) and imipenem 65% (2/16). CONCLUSION: For this geographically diverse PSA population, ceftolozane/tazobactam demonstrated the highest overall susceptibility (95%). Other antipseudomonal agents inclusive of the carbapenems displayed susceptibilities of 65–76%. In the era of escalating PSA resistance to the β-lactams, the potency of ceftolozane/tazobactam may represent an important clinical option. DISCLOSURES: D. P. Nicolau, Merck: Consultant, Grant Investigator and Speaker’s Bureau, Consulting fee, Research grant and Speaker honorarium.