Chemical genetic approaches for the discovery of bacterial cell wall inhibitors.

Antimicrobial resistance (AMR) in bacterial pathogens is a worldwide health issue. The innovation gap in discovering new antibiotics has remained a significant hurdle in combating the AMR problem. Currently, antibiotics target various vital components of the bacterial cell envelope, nucleic acid and protein biosynthesis machinery and metabolic pathways essential for bacterial survival. The critical role of the bacterial cell envelope in cell morphogenesis and integrity makes it an attractive drug target. While a significant number of in-clinic antibiotics target peptidoglycan biosynthesis, several components of the bacterial cell envelope have been overlooked. This review focuses on various antibacterial targets in the bacterial cell wall and the strategies employed to find their novel inhibitors. This review will further elaborate on combining forward and reverse chemical genetic approaches to discover antibacterials that target the bacterial cell envelope.

Targeting Superoxide dismutase confers enhanced Reactive Oxygen Species mediated eradication of Polymyxin B induced Acinetobacter baumannii persisters.

Bacterial persisters represent non-inheritable drug tolerant population that are linked to recalcitrance of infections in healthcare settings. The rise of antibiotic resistance and depletion of new antibiotics in drug discovery pipeline has made the task of persister eradication more daunting. In the present study, we report that treatment of Acinetobacter baumannii with the last resort antibiotic polymyxin B displays continuous variation in tolerance among different clinical isolates. Mechanistically, Polymyxin B persisters exhibit disruption of proton motive force led delocalisation of cell division protein to attain a growth arrested phenotype. Tolerance studies on mutant strains revealed that superoxide dismutase (sodB) activity is a major contributor in tolerance of A. baumannii to polymyxin B. Using a dual fluorescence based persister detection system, screening of various antibiotics was performed to eradicate polymyxin B induced persisters of A. baumannii Rifampicin exhibited eradication of polymyxin B tolerant population by log reduction of 6 in magnitude against different clinical isolates of A. baumannii We establish that enhanced generation of ROS by rifampicin leads to clearance of these polymyxin B persisters. It was further demonstrated, as a proof of concept, that rifampicin potentiates the killing of polymyxin B persisters in murine wound infection model. We found that the effects were linked to significant down regulation of sodB by rifampicin, which contributes to higher generation of ROS in polymyxin B tolerant cells. In view of these results, we propose that the combination of polymyxin B and rifampicin is an effective antipersister strategy in clearing polymyxin B induced A. baumannii persisters.

Does Silver in Different Forms Affect Bacterial Susceptibility and Resistance? A Mechanistic Perspective.

The exceptional increase in antibiotic resistance in past decades motivated the scientific community to use silver as a potential antibacterial agent. However, due to its unknown antibacterial mechanism and the pattern of bacterial resistance to silver species, it has not been revolutionized in the health sector. This study deciphers mechanistic aspects of silver species, i.e., ions and lysozyme-coated silver nanoparticles (L-Ag NPs), against E. coli K12 through RNA sequencing analysis. The obtained results support the reservoir nature of nanoparticles for the controlled release of silver ions into bacteria. This study differentiates between the antibacterial mechanism of silver species by discussing the pathway of their entry in bacteria, sequence of events inside cells, and response of bacteria to overcome silver stress. Controlled release of ions from L-Ag NPs not only reduces bacterial growth but also reduces the likelihood of resistance development. Conversely, direct exposure of silver ions, leads to rapid activation of the bacterial defense system leading to development of resistance against silver ions, like the well-known antibiotic resistance problem. These findings provide valuable insight on the mechanism of silver resistance and antibacterial strategies deployed by E. coli K12, which could be a potential target for the generation of aim-based and effective nanoantibiotics.

Formation and Characterization of Protein Corona Around Nanoparticles: A Review.

Recent years have witnessed unprecedented increase in the use of nanoparticles in various sectors viz. electronics, catalysis, agriculture, textile, cosmetics, bio-medicine, packaging, house-holds and food-associated consumer products. This has led to the inevitable release of nanoparticles into the environment, which can have negative impact on living beings. Humans can also be exposed to these nanoparticles either intentionally or accidently. Nanoparticles can enter in the human body through food chain, inhalation, open wounds, drugs and intravenous injections etc. In majority of these cases, the nanoparticles may pass through the various cell layers, cell sap and finally enter into the blood. Upon interaction with biological fluid, nanoparticles come in close proximity particularly to the proteins present in the fluid. The assembly of proteins surrounding the nanoparticle's surface is called as protein corona and their complex is known as protein-nanoparticle complex. Formation of protein corona is a vibrant and driving process, which plays a pivotal role in the functioning of nanoparticles in biological systems. Moreover, due to interaction of proteins with nanoparticles, conformational changes may occur in the native structure of protein, which may lead to change in the functioning of proteins towards its cellular interaction. The present review provides in-depth knowledge about the formation of protein corona around nanoparticles and the factors regulating this process. Further, it discusses various techniques that can be used for the protein corona analysis and obtaining information about molecular consequences upon nanoparticle's exposure. Finally, the functional aspects of protein-nanoparticle complex have been discussed in detail. In-depth understanding of protein-nanoparticles complex can be instrumental to generate well-suited nanoparticles with desired surface characteristics in the way to biological application.

Do physico-chemical properties of silver nanoparticles decide their interaction with biological media and bactericidal action? A review.

The unprecedented increase in antibiotic resistance in this era has resuscitated the attention of scientific community to exploit silver and its various species as antimicrobial agents. Plenty of studies have been done to measure the antimicrobial potential of silver species (cationic silver, metallic Ag0 or silver nanoparticles, silver oxide particulates etc.) and indicated that membrane damage, oxidative stress, protein dysfunction and DNA damage to be the possible cause of injury to the microbial cell. However, the precise molecular mechanism of their mode of action has remained unclear, which makes an obstacle towards the generation of potential antibacterial agent against various pathogenic and multidrug resistant (MDR) bacteria. In order to endeavor this issue, one should first have the complete understanding about the resistance mechanisms present in bacteria that can be a therapeutic target for the silver-based drug formulations. Apart from this, in-depth understanding of the interactions of various silver species (with the biological media) is a probable deciding factor for the synthesis of silver-based drug formulations because the particular form and physico-chemical properties of silver can ultimately decide their antimicrobial action. In context to above mentioned serious concerns, the present article aims to discuss the mechanisms behind the confrontation of bacteria against various drugs and the effect of physico-chemical properties of silver species on their bactericidal action as well as critically evaluates the available reports on bacterial transcriptomic and proteomic profiles upon the exposure of various silver species. Further, this review state the mechanism of action that needs to be followed for the complete understanding of toxic potential of silver nanoparticles, which will open a possibility to synthesize new silver nanoparticle based antimicrobial systems with desired properties to ensure their safe use, exposure over extended period and fate in human body and environment.