In Vivo Resistance to Ceftolozane/Tazobactam in Pseudomonas aeruginosa Arising by AmpC- and Non-AmpC-Mediated Pathways

Table 1

Antimicrobial susceptibility, β-lactamase overproduction assay, and carbapenemase production assay of P. aeruginosa strains.

Isolate	MIC (µg/ml)^a									CarbaNP
	FEP^b	PTZ^b	CZA^c	C/T^c	IMI^b	MER^b	DOR^b	CAZ^c
								MH^d	+ CLOX^d
PA2312	16	>128/4	4/4	2/4	32	32	64	1	1	NEG
PA2428	>32	>128/4	>64/4	64/4	32	32	16	≥256	24	NEG
HOU2365	32	>128/4	4/4	2/4	16	8	4	8	2	NEG
HOU2366	64	64/4	>64/4	>128/4	4	32	16	≥256	≥256	NEG

^aCAZ: ceftazidime; C/T: ceftolozane/tazobactam; CZA: ceftazidime/avibactam; DOR: doripenem; FEP: cefepime; IMI: imipenem; MER: meropenem; PTZ: piperacillin/tazobactam. ^bMIC determined by broth microdilution; ^cMIC determined by Etest; ^dceftazidime (CAZ) MIC as determined by Etest in the presence/absence of cloxacillin (CLOX) 1000 µg/ml.