The Transcriptomic Signature of Tigecycline in Acinetobacter baumannii.

Liping Li,Alaska Pokhrel,Ian T Paulsen,Sasha G Tetu,Karl A Hassan,Varsha Naidu,Amy K Cain

doi:10.3389/fmicb.2020.565438

Abstract

Tigecycline, a protein translation inhibitor, is a treatment of last resort for infections caused by the opportunistic multidrug resistance human pathogen Acinetobacter baumannii. However, strains resistant to tigecycline were reported not long after its clinical introduction. Translation inhibitor antibiotics perturb ribosome function and induce the reduction of (p)ppGpp, an alarmone involved in the stringent response that negatively modulates ribosome production. Through RNA sequencing, this study revealed a significant reduction in the transcription of genes in citric acid cycle and cell respiration, suggesting tigecycline inhibits or slows down bacterial growth. Our results indicated that the drug-induced reduction of (p)ppGpp level promoted the production but diminished the degradation of ribosomes, which mitigates the translational inhibition effect by tigecycline. The reduction of (p)ppGpp also led to a decrease of transcription coupled nucleotide excision repair which likely increases the chances of development of tigecycline resistant mutants. Increased expression of genes linked to horizontal gene transfer were also observed. The most upregulated gene, rtcB, involving in RNA repair, is either a direct tigecycline stress response or is in response to the transcription de-repression of a toxin-antitoxin system. The most down-regulated genes encode two β-lactamases, which is a possible by-product of tigecycline-induced reduction in transcription of genes associated with peptidoglycan biogenesis. This transcriptomics study provides a global genetic view of why A. baumannii is able to rapidly develop tigecycline resistance.

Highlights

Tigecycline is a broad-spectrum antibiotic derived from minocycline and was the first glycylcycline class antibiotic approved for clinical use (Petersen et al, 1999)
Because the A. baumannii doubling time at log phase is around 25 min and tigecycline slows down bacterial growth, this strain at mid-exponential growth phase was exposed to tigecycline at 2.5 μg/ml for 30 min, and the global transcriptomic response was analyzed via RNA-Seq
We used RNA-Seq to show that exposure to a sub-inhibitory concentration of tigecycline in A. baumannii affected transcription of genes involved in protein translation as expected, and resulted in significant gene transcriptional changes associated with RNA metabolism, DNA mismatch repair, horizontal gene transfer (HGT) and genetic element mobilization

Summary

Introduction

Tigecycline is a broad-spectrum antibiotic derived from minocycline and was the first glycylcycline class antibiotic approved for clinical use (Petersen et al, 1999). Tigecycline has increased antibacterial potency due to its higher binding affinity with the 70S ribosomes, or with the helix 31 and 34 of the16S rRNA on the head of the 30S subunit (Jenner et al, 2013). This effect inhibits the delivery of the thermo-unstable ternary complex elongation factor (EF-Tu)·GTP·aminoacyl-tRNA to the ribosomal A (aminoacyl) site and eventually perturbs polypeptide translation (Jenner et al, 2013). Plasmid- or mobile genetic element (MGE)borne tetX genes have been identified in tigecycline resistant bacterial isolates from clinical and animal husbandry settings (He et al, 2019, 2020; Sun et al, 2019; Wang et al, 2019)

Objectives

Methods

Results

Conclusion