Diverse modes of ceftazidime/avibactam resistance acquisition in carbapenem-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa from a Chinese intensive care unit.

OBJECTIVES

To investigate the mechanisms of ceftazidime/avibactam (CZA) resistance and the nosocomial dissemination of carbapenem-resistant Pseudomonas aeruginosa (CRPA) and carbapenem-resistant Klebsiella pneumoniae (CRKP) in an intensive care unit (ICU) in China.

METHODS

Clinical CRPA and CRKP isolates were obtained from an ICU of a tertiary hospital in China from August 2020 to February 2021. Antimicrobial susceptibility was determined according to CLSI. WGS, cloning experiments and kinetic parameters were conducted to reveal resistance mechanisms, molecular characteristics and dissemination of CRPA and CRKP.

RESULTS

We isolated 32 CZA-resistant strains, including 12 CRPA and 20 CRKP strains from an ICU between August 2020 and February 2021. CZA resistance was associated with the presence of NDM and efflux pumps in CRKP strains, whereas bla, bla, and bla contributed to CZA resistance in CRPA strains. Compared to KPC-2, KPC-87 exhibited a 1.5-fold elevation in k/K for ceftazidime, a 7.5-fold increase in K for avibactam, and a loss of carbapenem hydrolysis. bla was located in the NTE-IIa like element based on the Tn3. Insertion of 656 bp Δbla upstream of bla introduced an additional promoter that increased KPC-87 expression. Cluster 2 and 3 of CRKP represented two different clones of ST11 transmitted between patients. KPC-87-producing ST270 CRPA strains exhibited a small-scale dissemination and cross-regional transfer with the referral of a patient. The evolutionary pathways of AFM-2-producing ST275 CRPA strains were more complex to elucidate the transmission events.

CONCLUSIONS

In CRKP and CRPA, diverse resistance mechanisms contributed to CZA resistance. These CZA-resistant strains were transmitted among patients in the ICU and even across regions to the other healthcare unit when the patient was transferred.