In Vitro Activity of the Novel Tetracyclines, Tigecycline, Eravacycline, and Omadacycline, Against Moraxella catarrhalis

The tigecycline resistance mechanisms in Gram-negative bacilli

Tigecycline, hailed as a pivotal agent in combating multidrug-resistant bacterial infections, confronts obstacles posed by the emergence of resistance mechanisms in Gram-negative bacilli. This study explores the complex mechanisms of tigecycline resistance in Gram-negative bacilli, with a particular focus on the role of efflux pumps and drug modification in resistance. By summarizing these mechanisms, our objective is to provide a comprehensive understanding of tigecycline resistance in Gram-negative bacilli, thereby illuminating the evolving landscape of antimicrobial resistance. This review contributes to the elucidation of current existing tigecycline resistance mechanisms and provides insights into the development of effective strategies to manage the control of antimicrobial resistance in the clinical setting, as well as potential new targets for the treatment of tigecycline-resistant bacterial infections.

Characteristics of tetracycline antibiotic resistance gene enrichment and migration in soil-plant system

Tetracycline Resistance Genes (TRGs) have received widespread attention in recent years, as they are a novel environmental pollutant that can rapidly accumulate and migrate in soil plant systems through horizontal gene transfer (HGT), posing a potential threat to food safety and public health. This article systematically reviews the pollution sources, enrichment, and migration characteristics of TRGs in soil. The main sources of TRGs include livestock manure and contaminated wastewater, especially in intensive farming environments where TRGs pollution is more severe. In soil, TRGs diffuse horizontally between bacteria and migrate to plant tissues through mechanisms such as plasmid conjugation, integron mediation, and phage transduction. The migration of TRGs is not limited to the soil interior, and increasing evidence suggests that they can also enter the plant system through plant root absorption and the HGT pathway of endophytic bacteria, ultimately accumulating in plant roots, stems, leaves, fruits, and other parts. This process has a direct impact on human health, especially when TRGs are found in crops such as vegetables, which may be transmitted to the human body through the food chain. In addition, this article also deeply analyzed various factors that affect the migration of TRGs, including the residual level of tetracycline in soil, the type and concentration of microorganisms, heavy metal pollution, and the presence of new pollutants such as microplastics. These factors significantly affect the enrichment rate and migration mode of TRGs in soil. In addition, two technologies that can effectively eliminate TRGs in livestock breeding environments were introduced, providing reference for healthy agricultural production. The article concludes by summarizing the shortcomings of current research on TRGs, particularly the limited understanding of TRG migration pathways and their impact mechanisms. Future research should focus on revealing the migration mechanisms of TRGs in soil plant systems and developing effective control and governance measures to reduce the environmental transmission risks of TRGs and ensure the safety of ecosystems and human health.

Third-Generation Tetracyclines: Current Knowledge and Therapeutic Potential

Tetracyclines constitute a unique class of antibiotic agents, widely prescribed for both community and hospital infections due to their broad spectrum of activity. Acting by disrupting protein synthesis through tight binding to the 30S ribosomal subunit, their interference is typically reversible, rendering them bacteriostatic in action. Resistance to tetracyclines has primarily been associated with changes in pump efflux or ribosomal protection mechanisms. To address this challenge, tetracycline molecules have been chemically modified, resulting in the development of third-generation tetracyclines. These novel tetracyclines offer significant advantages in treating infections, whether used alone or in combination therapies, especially in hospital settings. Beyond their conventional antimicrobial properties, research has highlighted their potential non-antibiotic properties, including their impact on immunomodulation and malignancy. This review will focus on third-generation tetracyclines, namely tigecycline, eravacycline, and omadacycline. We will delve into their mechanisms of action and resistance, while also evaluating their pros and cons over time. Additionally, we will explore their therapeutic potential, analyzing their primary indications of prescription, potential future uses, and non-antibiotic features. This review aims to provide valuable insights into the clinical applications of third-generation tetracyclines, thereby enhancing understanding and guiding optimal clinical use.

Eravacycline: a comprehensive review of in vitro activity, clinical efficacy, and real-world applications

INTRODUCTION

The escalating threat of multidrug-resistant organisms necessitates constant exploration for novel antimicrobial agents. Eravacycline has emerged as a promising solution due to its unique chemical structure, which enhances potency and expands its spectrum of activity.

AREA COVERED

This review provides a thorough examination of eravacycline, encompassing its in vitro activity against Gram-positive and Gram-negative aerobes, carbapenem-non-susceptible organisms, anaerobes, and other bacterial strains. Additionally, it evaluates evidence from clinical studies to establish its clinical effect and safety.

EXPERT OPINION

Eravacycline, a synthetic fluorocycline, belongs to the tetracyclines class. Similar to other tetracycline, eravacycline exerts its antibacterial action by reversibly binding to the bacterial ribosomal 30S subunit. Eravacycline demonstrates potent in vitro activity against many Gram-positive and Gram-negative aerobes, anaerobes, and multidrug-resistant organisms. Randomized controlled trials and its associated meta-analysis affirm eravacycline's efficacy in treating complicated intra-abdominal infections. Moreover, real-world studies showcase eravacycline's adaptability and effectiveness in diverse clinical conditions, emphasizing its utility beyond labeled indications. Despite common gastrointestinal adverse events, eravacycline maintains an overall favorable safety profile, reinforcing its status as a tolerable antibiotic. However, ongoing research is essential for refining eravacycline's role, exploring combination therapy, and assessing its performance against biofilms, in combating challenging bacterial infections.

Mutation of TonB-Dependent Receptor Encoding Gene MCR_0492 Potentially Associates with Macrolides Resistance in Moraxella catarrhalis Isolates

Introduction

Moraxella catarrhalis, which is an opportunistic pathogen and is one of the three major pathogens of community-acquired pneumonia, causes a variety of infections in clinic. In recent years, the isolation rate of Moraxella catarrhalis has gradually increased. In China, due to the clinical empirical use of antibiotics, the resistance rate of Moraxella catarrhalis isolated from children to β-lactam antibiotics has reached 99%. The non-susceptible rate of Moraxella catarrhalis to macrolide antibiotics has also increased significantly.

Methods

Two isolates of Moraxella catarrhalis (R17123922_R and R18013231_R) were isolated from in-patients and were confirmed to be resistant to macrolide antibiotics using the standard disk diffusion and broth microdilution method recommended by CLSI. Whole-genome sequencing (WGS) analysis was performed in these two resistant strains.

Results

A total of 696 SNVs (single nucleotide variations), and 79 indels (Insertion and Deletion) were found in R17123922_R and R18013231_R. These SNVs and indels were distributed evenly in the genome, and no centralized distribution occurred. Moreover, two isolates did not harbor any previously reported mutations in the 23S rRNA and ribosomal proteins.

Conclusion

A novel indel in the MCR_0492 gene encoding TonB-dependent receptor protein was identified, and we speculated that TonB-dependent protein receptor may play an important role in macrolide resistance of Moraxella catarrhalis.