Zhen Shen1,2, Baixing Ding1,2, Meiping Ye1,2, Peng Wang3, Yingmin Bi1,2, Shi Wu1,2, Xiaogang Xu1,2, Qinglan Guo1,2, Minggui Wang1,2. 1. Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China. 2. Key Laboratory of Clinical Pharmacology of Antibiotics, National Health and Family Planning Commission of People's Republic of China, Shanghai, China. 3. Department of Infectious Diseases, Shanghai Jiaotong University Affiliated Sixth Hospital, Shanghai, China.
Abstract
Objectives: To investigate mechanisms for the decreased susceptibility to ceftazidime/avibactam in KPC-producing Klebsiella pneumoniae (KPC-KP). Methods: A total of 24 isolates, 8 each with ceftazidime/avibactam MICs of 4-8, 1-2 and ≤0.5 mg/L, were randomly selected from 214 clinical isolates of KPC-KP, and the β-lactamase hydrolysis activity and porin expression profiles were determined. Plasmid profile and relative expression and copy number of the bla KPC gene were also analysed. Results: Ceftazidime/avibactam MIC 50 and MIC 90 were 2 and 4 mg/L, respectively, for the 214 KPC-KP isolates. The hydrolysis activities of nitrocefin and ceftazidime in both of the ceftazidime/avibactam MIC 4-8 and 1-2 mg/L groups were significantly higher than those of the MIC ≤0.5 mg/L group, while the hydrolysis activities were 4-4.6-fold higher in the MIC 4-8 mg/L group than in the other two groups when 4 mg/L avibactam was added. The relative expression and copy number of the bla KPC gene in the MIC 4-8 mg/L group were 4.2-4.8-fold higher than in the other two groups. Meanwhile, SDS-PAGE showed that all isolates in the two groups with MIC ≥1 mg/L lacked OmpK35, which had either an early frameshift with a premature stop codon ( n = 15, ST11) or overexpression of the negative regulation genes, micF and ompR ( n = 1, ST15), whereas OmpK35 and OmpK36 could both be observed in all isolates with MIC ≤0.5 mg/L. Conclusions: Decreased ceftazidime/avibactam susceptibility in KPC-KP clinical isolates is caused by high ceftazidime hydrolysis activity and OmpK35 porin deficiency and the majority of isolates belong to ST11.
Objectives: To investigate mechanisms for the decreased susceptibility to ceftazidime/avibactam in KPC-producing Klebsiella pneumoniae (KPC-KP). Methods: A total of 24 isolates, 8 each with ceftazidime/avibactam MICs of 4-8, 1-2 and ≤0.5 mg/L, were randomly selected from 214 clinical isolates of KPC-KP, and the β-lactamase hydrolysis activity and porin expression profiles were determined. Plasmid profile and relative expression and copy number of the bla KPC gene were also analysed. Results:Ceftazidime/avibactam MIC 50 and MIC 90 were 2 and 4 mg/L, respectively, for the 214 KPC-KP isolates. The hydrolysis activities of nitrocefin and ceftazidime in both of the ceftazidime/avibactam MIC 4-8 and 1-2 mg/L groups were significantly higher than those of the MIC ≤0.5 mg/L group, while the hydrolysis activities were 4-4.6-fold higher in the MIC 4-8 mg/L group than in the other two groups when 4 mg/L avibactam was added. The relative expression and copy number of the bla KPC gene in the MIC 4-8 mg/L group were 4.2-4.8-fold higher than in the other two groups. Meanwhile, SDS-PAGE showed that all isolates in the two groups with MIC ≥1 mg/L lacked OmpK35, which had either an early frameshift with a premature stop codon ( n = 15, ST11) or overexpression of the negative regulation genes, micF and ompR ( n = 1, ST15), whereas OmpK35 and OmpK36 could both be observed in all isolates with MIC ≤0.5 mg/L. Conclusions: Decreased ceftazidime/avibactam susceptibility in KPC-KP clinical isolates is caused by high ceftazidime hydrolysis activity and OmpK35 porin deficiency and the majority of isolates belong to ST11.
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