Antibiotics: Precious Goods in Changing Times

Research Progress on Ti3C2Tx-Based Composite Materials in Antibacterial Field

The integration of two-dimensional Ti3C2Tx nanosheets and other materials offers broader application options in the antibacterial field. Ti3C2Tx-based composites demonstrate synergistic physical, chemical, and photodynamic antibacterial activity. In this review, we aim to explore the potential of Ti3C2Tx-based composites in the fabrication of an antibiotic-free antibacterial agent with a focus on their systematic classification, manufacturing technology, and application potential. We investigate various components of Ti3C2Tx-based composites, such as metals, metal oxides, metal sulfides, organic frameworks, photosensitizers, etc. We also summarize the fabrication techniques used for preparing Ti3C2Tx-based composites, including solution mixing, chemical synthesis, layer-by-layer self-assembly, electrostatic assembly, and three-dimensional (3D) printing. The most recent developments in antibacterial application are also thoroughly discussed, with special attention to the medical, water treatment, food preservation, flexible textile, and industrial sectors. Ultimately, the future directions and opportunities are delineated, underscoring the focus of further research, such as elucidating microscopic mechanisms, achieving a balance between biocompatibility and antibacterial efficiency, and investigating effective, eco-friendly synthesis techniques combined with intelligent technology. A survey of the literature provides a comprehensive overview of the state-of-the-art developments in Ti3C2Tx-based composites and their potential applications in various fields. This comprehensive review covers the variety, preparation methods, and applications of Ti3C2Tx-based composites, drawing upon a total of 171 English-language references. Notably, 155 of these references are from the past five years, indicating significant recent progress and interest in this research area.

Antibiotics: Precious Goods in Changing Times

Antibiotics represent a first line of defense of diverse microorganisms, which produce and use antibiotics to counteract natural enemies or competitors for nutritional resources in their nearby environment. For antimicrobial activity, nature has invented a great variety of antibiotic modes of action that involve the perturbation of essential bacterial structures or biosynthesis pathways of macromolecules such as the bacterial cell wall, DNA, RNA, or proteins, thereby threatening the specific microbial lifestyle and eventually even survival. However, along with highly inventive modes of antibiotic action, nature also developed a comparable set of resistance mechanisms that help the bacteria to circumvent antibiotic action. Microorganisms have evolved specific adaptive responses that allow to appropriately react to the presence of antimicrobial agents, thereby ensuring survival during antimicrobial stress. In times of rapid development and spread of antibiotic (multi-)resistance, new resistance-breaking strategies to counteract bacterial infections are desperately needed. This chapter is an update to Chapter 1 of the first edition of this book and intends to give an overview of common antibiotics and their target pathways. It will also present examples for new antibiotics with novel modes of action, illustrating that nature's repertoire of innovative new antimicrobial agents has not been fully exploited yet, and we still might find new drugs that help to evade established antimicrobial resistance strategies.

An efficient simultaneous degradation of sulfamethoxazole and trimethoprim by photoelectro-Fenton process under non-modified pH using a natural citric acid source: study of biodegradability, ecotoxicity, and antibacterial activity

In this work, the use of natural organic wastes (orange and lemon peels) as sources of citric acid was evaluated along with the application of the photoelectro-Fenton (PEF) system under non-modified pH as a novel alternative to degrade a complex mixture of pharmaceuticals: sulfamethoxazole (SMX-7.90 × 10^-5 mol/L) and trimethoprim (TMP-6.89 × 10^-5 mol/L). The system was equipped with a carbon felt air diffusion cathode (GDE) and a Ti/IrO₂ anode doped with SnO₂ (DSA). A 3.6 × 10^-5 mol/L solution of commercial citric acid was used as a reference. The pharmaceuticals' evolution in the mixture was followed by high-performance liquid chromatography (HPLC). The addition of natural products showed an efficient simultaneous degradation of the antibiotics (100% of SMX and TMP at 45 min and 90 min, respectively) similar to the performance produced by adding the commercial citric acid to the PEF system. Moreover, the addition of natural products allowed for an increment of biodegradability (100% removal of TOC by a modified Zahn Wellens test) and a decrease in ecotoxicity (0% in the bioassay with D. Magna) of the treated solutions. The antibacterial activity was eliminated after only 45 min of treatment, suggesting that the degradation by-products do not represent a significant risk to human health or the environment in general. Results suggest that, because of the efficient formation of Fe-citrate complexes, the PEF could be enhanced by the addition of natural organic wastes as a sustainable alternative ecological system for water contaminated pharmaceuticals. Additionally, the potential of reusing natural organic wastes has been exposed, contributing to an improved low-cost PEF by decreasing the environmental contamination produced by this type of waste.

Synthesis of Degraded Limonoid Analogs as New Antibacterial Scaffolds against Staphylococcus aureus

Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) have become serious infections in humans and ruminants. S. aureus strains are showing rapid changes to develop resistance in traditional antibiotic-containing systems. In the continuous fierce fight against the emergent multi-drug resistant bacterial strains, straightforward and scalable synthetic procedures to produce new active molecules are in demand. Analysis of molecular properties points to degraded limonoids as promising candidates. In this article, we report a simple synthetic approach to obtain degraded limonoid analogs as scaffolds for new antibacterial molecules. The minimum inhibitory concentrations against S. aureus were evaluated for the stereoisomer mixtures by the broth microdilution method. Analysis of results showed that the acetylated derivatives were the most active of them all.