Evaluation of EUCAST rapid antimicrobial susceptibility testing (RAST) for carbapenemase-producing Klebsiella pneumoniae with focus on KPC variants.

Purpose: To evaluate the efficacy of the EUCAST Rapid Antimicrobial Susceptibility Testing (RAST) on Klebsiella pneumoniae carrying various carbapenemases, with a focus on KPC variants.

Methods: A total of 130 carbapenemase-producing K. pneumoniae (CPKP), encompassing those harboring class A (KPC-2: n = 38; KPC variants: n = 30), class B (n = 42), class D (n = 4) and strains co-producing class A and class B carbapenemases (n = 16), were evaluated for susceptibility to seven antibiotics, including ceftazidime/avibactam (CAZ/AVI), using the EUCAST RAST. Results obtained after 6 h and 8 h of incubation were compared with those obtained by reference broth microdilution. Additionally, the capacity of the RAST method to screen for different types of carbapenemases was assessed.

Results: All 130 CPKP isolates generated 100% readable zones at both 6 h and 8 h, with overall categorical agreement (CA) rates of > 90% for all tested antibiotics. For isolates producing class A carbapenemases, particularly the KPC variants, the EUCAST RAST showed excellent performance in determining CAZ/AVI susceptibility, achieving 100% CA and no errors at each reading time. However, significant challenges arose for meropenem (MEM), characterized by low CA (73.9%) and high major errors (MEs, 20.1%) at 6 h reading. Extending incubation to 8 h dramatically improved the performance, while the proportion of strains within the ATU remained high (23.3% at 6 h; 30.0% at 8 h).

Conclusions: The EUCAST RAST can be effectively implemented in routine clinical laboratories, particularly in regions like China where K. pneumoniae carrying KPC-2 is widely prevalent. However, caution should be exercised when interpreting the results of MEM for KPC variants.