The exact mechanism behind the antibacterial efficacy of nanoparticles has remained unexplored to date. This study aims to shed light the mechanism adopted using magnesium oxide nanoparticles prepared in ethyl alcohol against gram-negative and gram-positive bacterial cells, and the generation of reactive oxygen species (ROS) is proposed to be the dominant mechanism. This paradigm is supported by the quantification of the hydroxyl radical and superoxide anions produced in the nanoparticle treated and untreated bacterial solutions, and by the reduction of the antibacterial efficiency after the addition of a radical scavenger. The production of free Mg2+ ions from the nanoparticle is supposed to be the causative agent behind this uncontrolled ROS generation, resulting in excessive oxidative stress, which the antioxidants of the bacterial cells are unable to nullify, leading to cell damage. The amount of proteins, carbohydrates and lipids leaked due to the distortion of the cellular membrane is also quantified, and it is observed that their leakage trend varies on the structure of the bacterial cell. FESEM images taken at certain time intervals show the gradual internalization of the nanoparticles, and increasing rupture of bacterial cell membranes, leading to cell necrosis.

An insight into the mechanism of antibacterial activity by magnesium oxide nanoparticles.

Antibiotics like colistin are the last resort to deal with infections by carbapenem-resistant Enterobacteriaceae (CREB). Resistance to colistin severely restricts therapeutic options. To tackle this dire situation, urgent measures to restore colistin sensitivity are needed. In this study, whole-genome sequencing of colistin-resistant E. coli strain was performed and the genome analysis revealed that the strain belonged to the sequence type ST405. Multiple mutations were observed in genes implicated in colistin resistance, especially those related to the L-Ara-4-N pathway but mgrB was unmutated and mcr1-9 genes were missing. MarR inhibitor salicylate was used to re-sensitize this strain to colistin, which increased the negative charge on the cell surface especially in colistin resistant E. coli (U3790 strain) and thereby facilitated a decrease in colistin MIC by 8 fold. It is indeed well known that MarR inhibition by salicylate triggers the expression of AcrAB efflux pumps through MarA. So, in order to fully restore colistin sensitivity, a potent efflux pump inhibitor (BC1), identified earlier by this group was employed. The combination of colistin with both salicylate and BC1 caused a remarkable 6 log reduction in cell counts of U3790 in time-kill assay. Infection of muscle tissue of zebrafish with U3790 followed by various treatments showed that the combination of colistin + salicylate + BC1 was highly effective in reducing bioburden in infected muscle tissue by 4 log fold. Thus, our study shows that a combination of MarR inhibitor to enhance colistin binding and efflux pump inhibitor to reduce colistin extrusion was highly effective in restoring colistin sensitivity in colistin-resistant clinical isolate of E. coli in vitro and in vivo.

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Restoring colistin sensitivity in colistin-resistant E. coli: Combinatorial use of MarR inhibitor with efflux pump inhibitor.

Urinary tract infection (UTI) is one of the most common bacterial infections in humans, with uropathogenic Escherichia coli (UPEC) the leading causative organism. UPEC has a number of virulence factors that enable it to overcome host defenses within the urinary tract and establish infection. The O antigen and the capsular polysaccharide are two such factors that provide a survival advantage to UPEC. Here we describe the application of the rpsL counter selection system to construct capsule (kpsD) and O antigen (waaL) mutants and complemented derivatives of three reference UPEC strains: CFT073 (O6:K2:H1), RS218 (O18:K1:H7) and 1177 (O1:K1:H7). We observed that while the O1, O6 and O18 antigens were required for survival in human serum, the role of the capsule was less clear and linked to O antigen type. In contrast, both the K1 and K2 capsular antigens provided a survival advantage to UPEC in whole blood. In the mouse urinary tract, mutation of the O6 antigen significantly attenuated CFT073 bladder colonization. Overall, this study contrasts the role of capsule and O antigen in three common UPEC serotypes using defined mutant and complemented strains. The combined mutagenesis-complementation strategy can be applied to study other virulence factors with complex functions both in vitro and in vivo.

Role of capsule and O antigen in the virulence of uropathogenic Escherichia coli

Free living, cosmopolitan amoebae from Acanthamoeba genus present a serious risk to human health. As facultative human parasites, these amoebae may cause Acanthamoeba keratitis (AK). Acanthamoeba keratitis is a severe, vision-threatening corneal infection with non-specific symptoms. The number of reported AK cases worldwide has been increasing every year. Moreover, 90% of Acanthamoeba keratitis cases are related to contact lens use. Wearing and storage contact lenses not in accordance with the physicians and manufacturers recommendations are the primary key risk factors of this disease. Amoebae can easily adhere to the contact lens surface and transmit to the corneal epithelium. Preventing amoebae adhesion to the contact lens surface could significantly decrease the number of AK infections. Until now, the effective therapy against AK is still under development. Currently proposed therapies are mainly limited to the chlorhexidine digluconate combined with propamidine isethionate or hexamidine applications, which are insufficient and very toxic to the eye. Due to lack of effective treatment, looking for new potential preventive agents is crucial to decrease the number of Acanthamoeba keratitis infections, especially among contact lens users. Nanoparticles have been already included in several novel therapies against bacteria, viruses, fungi, and protist. However, their anti-amoebic potential has not been fully tested yet. The aim of this study was to assess silver nanoparticles (AgNPs) and platinum nanoparticles (PtNPs) anti-amoebic activity and influence on the amoebae adhesion to the surface of four different groups of contact lenses—classified according to the Food and Drugs Administration (FDA) guidelines. The obtained results show that both tested nanoparticles were effective against Acanthamoeba trophozoites and decreased the amoebae adhesion to the contact lens surface. AgNPs showed better anti-amoebic activity to cytotoxicity dependence and reduced amoebae adhesion in a wider spectrum of the tested contact lenses. Our studies also confirmed that ionization next to hydration of the contact lens material is a crucial parameter influencing the Acanthamoeba adhesion to the contact lens surface. In conclusion, silver nanoparticles might be considered as a novel preventive agent against Acanthamoeba keratitis infection.

https://www.mdpi.com/2076-0817/9/5/350/pdf

Silver Nanoparticles as a Novel Potential Preventive Agent against Acanthamoeba Keratitis.

Plantinum nanoparticles (Pt NPs) have huge potential as heterogeneous catalyst, chemiresistor coating material, nanomedicine, nanosensor, and electronic components along with various other industrial applications. Physical, chemical as well as biological methods are used for the synthesis of plantinum NPs. Physical methods depend upon the physical phenomenon for Pt NPs synthesis. Chemical methods involve one or other chemical reactions to prepare Pt NPs. Biological methods are preferred over other methods. Among all biological sources, use of plant extracts for Pt NPs synthesis is safe and cost-effective. Pt NPs have application in catalysis, electronics, nanodiagnosis and nanomedicine. Synthesis of diverse Pt NPs using different plant bioresource may be more useful for various in vivo applications in future.

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Platinum Nanoparticles: Synthesis Strategies and Applications

Drug resistance traits are rapidly disseminated across bacteria by horizontal gene transfer, especially through plasmids. Plasmid curing agents that are active both in vitro and in vivo will resensitize Multi Drug Resistant (MDR) bacteria to antimicrobial agents. Pectin capped platinum nanoparticles (PtNPs) at sub MIC (20 µM) concentration was effective, in causing loss of Extended Spectrum Beta Lactamase (ESBL) harboring plasmid as evidenced by, absence of plasmid in agarose gel and by a concomitant (16–64 fold) drop in MIC for cell wall inhibitors ceftriaxone and meropenem, in carbapenem resistant Escherichia coli (CREC). Interestingly, the plasmid cured strain exhibited small colony morphology and displayed slower growth both in vitro and in vivo. Complementation of cured strain with plasmid from the wild type strain restored resistance towards meropenem and ceftriaxone. Relative to wild type, plasmid cured strain displayed 50% reduction in biofilm formation. Plasmid curing also occurred in vivo in infected zebrafish with curing efficiency of 17% for nanoparticle + meropenem treatment. PtNPs + meropenem reduced bioburden of CREC in infected zebrafish by 2.4 log CFU. Mechanistic studies revealed that nanoparticle interacted with cell surface and perturbed inner membrane integrity. PtNPs did not induce ROS, yet it caused plasmid DNA cleavage, as evidenced by gyrase inhibition assay. Our study for the first time reveals that PtNPs as plasmid curing agent can resensitize MDR bacteria to selective antimicrobial agents in vivo.

Gagana Rangappa

Papers

Sub lethal levels of platinum nanoparticle cures plasmid and in combination with carbapenem, curtails carbapenem resistant Escherichia coli