Mutations in ompK36 differentially impact in vitro synergy of meropenem/vaborbactam and ceftazidime/avibactam in combination with other antibiotics against KPC-producing Klebsiella pneumoniae.

Objectives: Ceftazidime/avibactam and meropenem/vaborbactam are preferred agents for Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-Kp) infections and are often used in combination with other agents. We aimed to characterize the synergy of combinations against KPC-Kp with varying ompK36 genotypes. Methods: KPC-Kp that harboured ompK36 WT, IS5 or glycine-aspartic acid duplication (GD) genotypes were selected. MICs were determined in triplicate. Synergy was assessed by time-kill assays for ceftazidime/avibactam and meropenem/vaborbactam in combination with colistin, gentamicin, tigecycline, meropenem or fosfomycin against 1 × 108 cfu/mL KPC-Kp. Results: KPC-Kp harboured ompK36 WT (n = 5), IS5 (n = 5) or GD (n = 5); 11 were KPC-2 and 4 were KPC-3. All were susceptible to ceftazidime/avibactam and meropenem/vaborbactam. In time-kill analysis, ceftazidime/avibactam and meropenem/vaborbactam 1 × MIC exhibited mean 24 h log-kills of -2.01 and -0.84, respectively. Ceftazidime/avibactam was synergistic in combination with colistin independent of ompK36 genotype. Ceftazidime/avibactam combinations impacted by porin mutations (compared to WT) were meropenem (-5.18 versus -6.62 mean log-kill, P < 0.001) and fosfomycin (-3.98 versus -6.58, P = 0.058). Mean log-kills with meropenem/vaborbactam were greatest in combination with gentamicin (-5.36). In the presence of porin mutations, meropenem/vaborbactam killing activity was potentiated by the addition of colistin (-6.65 versus -0.70, P = 0.03) and fosfomycin (-3.12 versus 1.54, P = 0.003). Conclusions: Our results shed new light on the synergy of ceftazidime/avibactam and meropenem/vaborbactam combinations against KPC-Kp with or without porin mutations. Killing activity of ceftazidime/avibactam with other cell wall active agents was decreased against isolates with porin mutations. On the other hand, some meropenem/vaborbactam combinations demonstrated enhanced killing in the presence of porin mutations.

Impact of ompk36 genotype and KPC subtype on the in vitro activity of ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam against KPC-producing K. pneumoniae clinical isolates.

Objectives: The availability of new ß-lactam/ß-lactamase inhibitors ceftazidime/avibactam, meropenem/vaborbactam and imipenem/relebactam have redefined contemporary treatment of Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) infections. We aimed to characterize and contrast the in vitro activity of these agents against genetically diverse KPC-Kp clinical isolates. Methods: We analysed genomes of 104 non-consecutive KPC-Kp isolates and compared the in vitro antibiotic activity by KPC subtype and ompK36 genotype. MICs were determined in triplicate by CLSI methods. Twenty representative isolates were selected for time-kill analyses against physiological steady-state and trough concentrations, as well as 4× MIC for each agent. Results: Fifty-eight percent and 42% of isolates harboured KPC-2 and KPC-3, respectively. OmpK36 mutations were more common among KPC-2- compared with KPC-3-producing Kp (P < 0.0001); mutations were classified as IS5 insertion, glycine-aspartic acid insertion at position 134 (GD duplication) and other mutations. Compared to isolates with WT ompK36, ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam MICs were elevated for isolates with IS5 by 2-, 4- and 16-fold, respectively (P < 0.05 for each). Against isolates with GD duplication, imipenem/relebactam and meropenem/vaborbactam MICs were increased, but ceftazidime/avibactam MICs were not. In time-kill studies, ceftazidime/avibactam-mediated killing correlated with ceftazidime/avibactam MICs, and did not vary across ompK36 genotypes. Imipenem/relebactam was not bactericidal against any isolate at trough concentrations. At steady-state imipenem/relebactam concentrations, regrowth occurred more commonly for isolates with IS5 mutations. Log-kills were lower in the presence of meropenem/vaborbactam for isolates with GD duplication compared with IS5 mutations. Conclusions: Our investigation identified key genotypes that attenuate, to varying degrees, the in vitro activity for each of the new ß-lactam/ß-lactamase inhibitors. Additional studies are needed to translate the importance of these observations into clinical practice.

In Vitro Susceptibility of Multidrug-Resistant Pseudomonas aeruginosa following Treatment-Emergent Resistance to Ceftolozane-Tazobactam.

We compared the in vitro susceptibility of multidrug-resistant Pseudomonas aeruginosa isolates collected before and after treatment-emergent resistance to ceftolozane-tazobactam. Median baseline and postexposure ceftolozane-tazobactam MICs were 2 and 64 µg/ml, respectively. Whole-genome sequencing identified treatment-emergent mutations in ampC among 79% (11/14) of paired isolates. AmpC mutations were associated with cross-resistance to ceftazidime-avibactam but increased susceptibility to piperacillin-tazobactam and imipenem. A total of 81% (12/16) of ceftolozane-tazobactam-resistant isolates with ampC mutations were susceptible to imipenem-relebactam.