Non-susceptibilities to antibiotics against important Gram-negative bacteria, and imipenem-relebactam, meropenem-vaborbactam against carbapenem non-susceptible Enterobacterales and Pseudomonas aeruginosa isolates implicated in complicated intra-abdominal and urinary tract infections in Taiwan, 2019

Introduction: Susceptibility of isolates of top-ranking Enterobacterales species and Pseudomonas aeruginosa implicated in complicated intra-abdominal infections (cIAI) and urinary tract infections (cUTI) to important antibiotics, including imipenem-relebactam (IMR) and meropenem-vaborbactam (MVB), in Taiwan in 2019 were evaluated. Methods: MICs to various antibiotics were determined using broth microdilution method. Susceptibility results were interpreted mainly based on the MIC breakpoints of the Clinical and Laboratory Standards Institute (CLSI) 2021, but susceptibilities of IMR and MVB were interpreted based on the CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) 2021. Resistance genes amongst carbapenem-non-susceptible (NS) Gram-negative bacteria (GNB) were investigated using multiplex polymerase chain reaction (PCR). Escherichia coli (n = 356), Klebsiella pneumoniae (n = 165) and Enterobacter cloacae complex (n = 42) isolates accounted for 85.3% of the 660 Enterobacterales isolates. Results: The non-susceptibility rates of imipenem (IPM), IMR against isolates of non-Morganellaceae Enterobacterales, and meropenem (MEM), MVB against all Enterobacterales isolates were 92.2%/94.8%, 98.4–98.7%/98.4–99%, 95%/98.2% and 98.8–100%/99.4–100% for the cIAI/cUTI subgroups, respectively. Amongst the 40 IPM-NS-non-Morganellaceae Enterobacterales isolates, when the CLSI 2021 criteria were applied, 10 were NS to IMR, and four Klebsiella pneumoniae isolates (harbouring bla_KPC but neither bla_MBL nor bla_OXA-48-like genes) were NS to IMR and MVB. Amongst the 93 Pseudomonas aeruginosa isolates under evaluation, the addition of relebactam (4 mg/L) resulted in a 4-to-16-fold reduction in the MICs of IPM in all 15 IPM-NS-Pseudomonas aeruginosa isolates (including 10 porin-deficient ones) not harbouring bla_MBL/bla_OXA-48-like genes. Contrastingly, the addition of vaborbactam (8 mg/L) improved the non-susceptibility to MEM in one (20%) of five IPM/MEM-NS Pseudomonas aeruginosa isolates. Conclusion: Continuous monitoring of susceptibility to clinically important GNB is warranted.