关键词: 铜绿假单胞菌, 头孢他啶?阿维巴坦, 耐药性, 三代测序

Abstract: Objective　To perform single⁃molecule, real⁃time sequencing of ceftazidime⁃avibactam (CAZ⁃AVI)⁃resistant Pseudomonas aeruginosa and to investigate the mechanism underlying ceftazidime⁃avibactam resistance in P. aeruginosa.  Methods    The susceptibility of 89 P. aeruginosa isolates randomly sampled from clinical specimens in Sanming First Hospital Affiliated to Fujian Medical University from November 2021 through July 2023 to common antimicrobial agents was tested, and the minimum inhibitory concentration (MIC) of CAZ⁃AVI was determined against P. aeruginosa with a broth microdilution assay, with CAZ⁃AVI MICs of 8 mg/L and lower defined as susceptible and 16 mg/L and higher as resistant. The expression of drug⁃resistant genes ampC, oxa⁃488, oprD, mexA, oxa⁃10, oxa⁃14, vim and tem was quantified in P. aeruginosa using a real⁃time quantitative reverse transcription PCR (qPCR) assay. CAZ⁃AVI⁃susceptible and ⁃resistant P. aeruginosa isolates from the same case were selected for PacBio single⁃molecule, real⁃time sequencing, and sequencing results were subjected to genome structure and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotations.  Results　The 89 P. aeruginosa isolates showed a relatively high level of resistance to meropenem (75.28%) and imipenem (74.16%) and the highest susceptibility to amikacin (91.01%). There were 49 CAZ⁃AVI⁃resistant P. aeruginosa isolates and 40 susceptible isolates. qPCR assay detected lower oprD gene expression in CAZ⁃AVI⁃resistant P. aeruginosa isolates [0.104 (2.385)] than in susceptible isolates [0.551 (17.885)] (Z = -2.958, P < 0.01), and there were no significant differences between CAZ⁃AVI⁃susceptible and ⁃resistant P. aeruginosa isolates in terms of ampC, oxa⁃488, mexA or tem gene expression (all P values > 0.05), while oxa⁃10, oxa⁃14 and vim gene was expressed in few P. aeruginosa isolates. There were 1 729, 3 936, 3 737 and 3 955 genes in CAZ⁃AVI⁃resistant P. aeruginosa isolates PA⁃762 and PA⁃M174 and susceptible isolates PA⁃885 and PA⁃808 that were annotated to GO terms, with the highest numbers of genes enriched in the molecular function of catalytic activity, high numbers of genes enriched in biological processes of metabolic process, single⁃organism process and cellular process, and high numbers of genes enriched in cellular components of cell and cell membranes. There were 1 803, 4 084, 3 915 and 4 066 genes in the PA⁃762, PA⁃M174, PA⁃885 and PA⁃808 isolates enriched in the KEGG signaling pathway, and the majority of genes were enriched in four primary signaling pathways of metabolism, genetic information processing, environmental information processing and cellular process, with the highest number of genes associated with metabolic pathways. Both CAZ⁃AVI⁃resistant P. aeruginosa isolates PA⁃762 and PA⁃M174 carried multiple efflux pumps systems, including MexAB⁃OprM, MexCD⁃OprJ, MexEF⁃OprN and MexXY⁃OprM. Single nucleotide substitution was found at position 169 in the DNA sequence of the PA⁃762 isolate, leading to substitution of serine for glycine at position 57 in the protein sequence, and there are deletions of two bases at positions 307 and 308 in the DNA sequence of the PA⁃M174 isolate, leading to substitution of threonine for arginine at position 103 in the protein sequence.  Conclusion　Mutation or downregulation of oprD gene may lead to CAZ⁃AVI resistance in P. aeruginosa.

Key words: Pseudomonas aeruginosa, Ceftazidime?avibactam, Drug resistance, Single?molecule, real?time sequencing