Methods: Multiple US hospitals provided non-duplicate respiratory and blood isolates of PSA for potency testing. MICs against PSA were determined using broth microdilution methods according to CLSI for 7 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 US provided total of 560 PSA isolates. Of the antibiotics assessed, %S to C/T was the highest at 95% with an MIC50 of 1µg/ml and MIC90 of 2µg/ml. In comparison, other %S (MIC50 / MIC90) 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.
S. Almarzoky Abuhussain,
D. P. Nicolau, Merck: Consultant , Grant Investigator and Speaker's Bureau , Consulting fee , Research grant and Speaker honorarium .