European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology · 2026
Performance evaluation of antimicrobial susceptibility testing methods for ceftazidime-avibactam and imipenem-relebactam against Klebsiella pneumoniae and Pseudomonas aeruginosa.
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Xu Xiaobo, Lu Erjie, Wu Lixin
Аннотация
BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CR-KP) and Pseudomonas aeruginosa (CR-PA) present critical therapeutic challenges. Ceftazidime-avibactam (CAZ-AVI) and imipenem-relebactam (IMI-REL) are key treatment options, but optimal susceptibility testing methods and local resistance mechanisms need clarification.
METHODS: A total of 108 CR‑KP and 102 CR‑PA non‑duplicate clinical isolates (June 2025-February 2026) were tested. Susceptibility to CAZ‑AVI and IMI‑REL was determined by broth microdilution (BMD, reference method), gradient diffusion, and Kirby‑Bauer (K‑B) disk diffusion. Essential agreement (EA), categorical agreement (CA), and error rates were calculated. Carbapenemase types were detected by immunochromatography (CARBA5).
RESULTS: By BMD, CAZ-AVI susceptibility rates were 88.9% for CR-KP and 96.1% for CR-PA; IMI-REL susceptibility rates were 84.3% and 75.5%, respectively. For CAZ-AVI, gradient diffusion showed excellent CA with BMD (99.1% for CR-KP and 94.1% for CR-PA) and EA of 91.7% and 97.1%, respectively. In contrast, gradient diffusion for IMI-REL was suboptimal (CA 94.4% and EA 86.1% for CR-KP, and CA 84.3% and EA 87.3% for CR-PA). K-B disk diffusion performed poorly for IMI-REL (CA 75.0% for CR-KP and 77.5% for CR-PA; minor errors rates were 24.1% and 20.6%, respectively).
CONCLUSION: CAZ-AVI and IMI-REL retain potent in vitro activity against contemporary CR-KP and CR-PA isolates. Gradient diffusion is a reliable alternative to BMD for ceftazidime-avibactam, whereas its accuracy is limited for imipenem-relebactam. K-B disk diffusion for IMI-REL is associated with unacceptably high error rates; reference method confirmation is recommended for isolates yielding non-susceptible results by this method.
METHODS: A total of 108 CR‑KP and 102 CR‑PA non‑duplicate clinical isolates (June 2025-February 2026) were tested. Susceptibility to CAZ‑AVI and IMI‑REL was determined by broth microdilution (BMD, reference method), gradient diffusion, and Kirby‑Bauer (K‑B) disk diffusion. Essential agreement (EA), categorical agreement (CA), and error rates were calculated. Carbapenemase types were detected by immunochromatography (CARBA5).
RESULTS: By BMD, CAZ-AVI susceptibility rates were 88.9% for CR-KP and 96.1% for CR-PA; IMI-REL susceptibility rates were 84.3% and 75.5%, respectively. For CAZ-AVI, gradient diffusion showed excellent CA with BMD (99.1% for CR-KP and 94.1% for CR-PA) and EA of 91.7% and 97.1%, respectively. In contrast, gradient diffusion for IMI-REL was suboptimal (CA 94.4% and EA 86.1% for CR-KP, and CA 84.3% and EA 87.3% for CR-PA). K-B disk diffusion performed poorly for IMI-REL (CA 75.0% for CR-KP and 77.5% for CR-PA; minor errors rates were 24.1% and 20.6%, respectively).
CONCLUSION: CAZ-AVI and IMI-REL retain potent in vitro activity against contemporary CR-KP and CR-PA isolates. Gradient diffusion is a reliable alternative to BMD for ceftazidime-avibactam, whereas its accuracy is limited for imipenem-relebactam. K-B disk diffusion for IMI-REL is associated with unacceptably high error rates; reference method confirmation is recommended for isolates yielding non-susceptible results by this method.