Role of bla(TEM) and OmpC in the piperacillin-tazobactam resistance evolution by E. coli in patients with complicated intra-abdominal infection

Piperacillin-tazobactam resistance (P/T-R) is increasingly reported among Escherichia coli isolates. Although in vitro experiments have suggested that bla(TEM) gene plays a key role in the P/T-R acquisition, no clinical in vivo study has yet confirmed the role of bla(TEM) or other genes. Therefore, we aimed to identify the mechanisms underlying P/T-R by following up patients with E. coli complicated intra-abdominal infections (cIAI) who experienced P/T treatment failure. Four pairs of strains, clonally related from four patients, were isolated both before and after treatment with P/T dosed at 4 g/0.5 g intravenously. The P/T MIC was tested using broth microdilution, and beta-lactamase activity was determined in these isolates. Whole-genome sequencing (WGS) was performed to decipher the role of bla(TEM) and other genes associated with P/T-R. Changes in the outer membrane protein (OMP) profile were analyzed using SDS-PAGE, and bla(TEM) and ompC transcription levels were measured by RT-qPCR. In addition, in vitro competition fitness was performed between each pairs of strains (P/T-susceptible vs. P/T-resistant). We found a higher copy number of bla(TEM) gene in P/T-R isolates, generated by three different genetic events: (1) IS26-mediated duplication of the bla(TEM) gene, (2) generation of a small multicopy plasmid (ColE-like) carrying bla(TEM), and (3) adaptive evolution via reduction of plasmid size, leading to a higher plasmid copy number. Moreover, two P/T-R strains showed reduced expression of OmpC. This study describes the mechanisms involved in the acquisition of P/T-R by E. coli in patients with cIAI. The understanding of P/T-R evolution is crucial for effectively treating infected patients and preventing the spread of resistant microorganisms. (c) 2023 The Author(s). Published by Elsevier Ltd on behalf of The British Infection Association. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study aimed to identify the mechanisms underlying Piperacillin-tazobactam resistance (P/T-R) in Escherichia coli. The results showed that P/T-R isolates had a higher copy number of the bla(TEM) gene, generated by three different genetic events. In addition, reduced expression of OmpC was observed in two P/T-R strains. This study provides important insights into the acquisition of P/T-R in E. coli, which is crucial for effective treatment and prevention of resistant microorganisms.