Ceftolozane-Tazobactam against Pseudomonas aeruginosa Cystic Fibrosis Clinical Isolates in the Hollow-Fiber Infection Model: Challenges Imposed by Hypermutability and Heteroresistance

Abstract

Pseudomonas aeruginosa remains a challenge in chronic respiratory infections in cystic fibrosis (CF). Ceftolozane-tazobactam has not yet been evaluated against multidrug-resistant hypermutable P. aeruginosa isolates in the hollow-fiber infection model (HFIM). Isolates CW41, CW35, and CW44 (ceftolozane-tazobactam MICs of 4, 4, and 2 mg/L, respectively) from adults with CF were exposed to simulated representative epithelial lining fluid pharmacokinetics of ceftolozane-tazobactam in the HFIM. Regimens were continuous infusion (CI; 4.5 g/day to 9 g/day, all isolates) and 1-h infusions (1.5 g every 8 hours and 3 g every 8 hours, CW41). Whole-genome sequencing and mechanism-based modeling were performed for CW41. CW41 (in four of five biological replicates) and CW44 harbored preexisting resistant subpopulations; CW35 did not. For replicates 1 to 4 of CW41 and CW44, 9 g/day CI decreased bacterial counts to <3 log₁₀ CFU/mL for 24 to 48 h, followed by regrowth and resistance amplification. Replicate 5 of CW41 had no preexisting subpopulations and was suppressed below ~3 log₁₀ CFU/mL for 120 h by 9 g/day CI, followed by resistant regrowth. Both CI regimens reduced CW35 bacterial counts to <1 log₁₀ CFU/mL by 120 h without regrowth. These results corresponded with the presence or absence of preexisting resistant subpopulations and resistance-associated mutations at baseline. Mutations in ampC, algO, and mexY were identified following CW41 exposure to ceftolozane-tazobactam at 167 to 215 h. Mechanism-based modeling well described total and resistant bacterial counts. The findings highlight the impact of heteroresistance and baseline mutations on the effect of ceftolozane-tazobactam and limitations of MIC to predict bacterial outcomes. The resistance amplification in two of three isolates supports current guidelines that ceftolozane-tazobactam should be utilized together with another antibiotic against P. aeruginosa in CF.

Keywords: dynamic in vitro model; mechanism-based modeling; pharmacodynamics; whole-genome sequencing.

FIG 1

Observed ceftolozane concentrations in the hollow-fiber infection model arising from ceftolozane-tazobactam (C/T) regimens. The data were fitted with a one-compartmental PK mathematical model simulating ELF concentrations in adult patients with cystic fibrosis (clearance = 5.2 L/h) (61–63).

FIG 2

Population model fits of the mathematical modeling of hypermutable P. aeruginosa isolate CW41 challenged with ceftolozane-tazobactam (C/T) via continuous infusion (CI) in the hollow-fiber infection model on antibiotic-free CAMHA plates (A) and plates containing ceftolozane-tazobactam (B and C). Data below the limit of counting are plotted at 1 log₁₀ CFU/mL.

FIG 3

Population model fits of the mathematical modeling of hypermutable P. aeruginosa isolate CW41 challenged with ceftolozane-tazobactam (C/T) via intermittent 8-hourly infusions (q8h) in the hollow-fiber infection model on antibiotic-free CAMHA plates (A) and plates containing ceftolozane-tazobactam (B and C). Data below the limit of counting are plotted at 1 log₁₀ CFU/mL.