# A novel mutation of ramR involved in tigecycline resistance in Klebsiella pneumoniae

## TL;DR

The study identifies a new mutation in the ramR gene of Klebsiella pneumoniae that causes resistance to the antibiotic tigecycline.

## Contribution

A novel two-base pair deletion mutation in the ramR gene is shown to confer tigecycline resistance in Klebsiella pneumoniae.

## Key findings

- A two-base pair deletion (g. 517_518 del) in the ramR gene was found in tigecycline-resistant Klebsiella pneumoniae strains.
- The ramR gene showed upregulated expression in all tigecycline-induced strains.
- The g. 517_518 del mutation in ramR is associated with sustained tigecycline resistance.

## Abstract

This study aims to investigate the novel potential tigecycline resistance mechanism in Klebsiella pneumoniae and provide new insights for the clinical treatment of infections caused by carbapenem-resistant Klebsiella pneumoniae. In vitro experiments were conducted to induce tigecycline resistance in Klebsiella pneumoniae, simulating potential genetic mutations that may arise under the selective pressure of tigecycline in clinical settings. Next-generation sequencing and real-time quantitative PCR (RT-qPCR) were employed to analyze bacterial genomic mutations and the transcription of related genes, respectively. Gene knockout technology, broth microdilution method, and resistance stability tests were utilized to further validate the function of the identified gene mutation sites. A novel two-base pair deletion mutation (position 517-518) in the ramR gene (g. 517_518 del) was identified in Klebsiella pneumoniae strains cultured in broth medium containing progressively increasing concentrations of tigecycline (4, 8, and 16 mg/L). The impact of this mutation on tigecycline resistance was characterized. The RT-qPCR analysis revealed a consistent upregulation of ramR expression across all tigecycline-induced strains, with significant elevation observed at various concentrations (0.5, 1, 2, 4, 8, and 16 mg/L). Furthermore, the g. 517_518 del mutation in ramR was associated with sustained tigecycline resistance. This study illustrated a novel ramR mutation, leading to tigecycline resistance in Klebsiella pneumoniae.

In this study, a novel missense mutation (g. 517_518 del GC) was detected in the ramR of tigecycline-induced Klebsiella pneumoniae, which was conducted in vitro, and the effects of anti-tigecycline caused by this mutation in ramR were confirmed. A high expression of ramR was observed in all tigecycline-induced strains. In addition, g. 517_518 del GC in ramR maintained tigecycline resistance. In summary, we illustrated a novel mutation of ramR, leading to tigecycline resistance in Klebsiella pneumoniae.