Innovative Insights into In Vitro Activity of Colloidal Platinum Nanoparticles against ESBL-Producing Strains of Escherichia coli and Klebsiella pneumoniae

Growing morbidity and mortality rates due to increase in the number of infections caused by MDR (multi-drug resistant) microorganisms are becoming some of the foremost global health issues. Thus, the need to search for and find novel approaches to fight AMR (antimicrobial resistance) has become obligatory. This study aimed to determine the antimicrobial properties of commercially purchased colloidal platinum nanoparticles by examining the existence and potency of their antibacterial effects and investigating the mechanisms by means of which they express these activities. Antimicrobial properties were investigated with respect to standard laboratory ATCC (American Type Cell Culture) and clinical extended-spectrum beta-lactamase (ESBL)-producing strains of Escherichia (E.) coli and Klebsiella (K.) pneumoniae. Standard microbiological methods of serial microdilution, modulation of microbial cell death kinetics (“time–kill” assays), and biofilm inhibition were used. Bacterial cell wall damage and ROS (reactive oxygen species) levels were assessed in order to explore the mechanisms of platinum nanoparticles’ antibacterial activities. Platinum nanoparticles showed strong antibacterial effects against all tested bacterial strains, though their antibacterial effects were found to succumb to time kinetics. Antibiofilm activity was modest overall and significantly effective only against E. coli strains. By measuring extracellular DNA/RNA and protein concentrations, induced bacterial cell wall damage could be assumed. The determination of ROS levels induced by platinum nanoparticles revealed their possible implication in antibacterial activity. We conclude that platinum nanoparticles exhibit potent antibacterial effects against standard laboratory and resistant strains of E. coli and K. pneumoniae. Both, cell wall damage and ROS induction could have important role as mechanisms of antibacterial activity, and, require further investigation.

Platinum nanoparticles in nanobiomedicine

Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

Size-Controlled Formation of Noble-Metal Nanoparticles in Aqueous Solution with a Thiol-Free Tripeptide

A combinatorial screening revealed the peptide H-His-d-Leu-d-Asp-NH2 (1) as an additive for the generation of monodisperse, water-soluble palladium nanoparticles with average diameters of 3 nm and stabilities of over 9 months. The tripeptide proved to be also applicable for the size-controlled formation of other noble-metal nanoparticles (Pt and Au). Studies with close analogues of peptide 1 revealed a specific role of each of the three amino acids for the formation and stabilization of the nanoparticles. These data combined with microscopic and spectroscopic analyses provided insight into the structure of the self-assembled peptidic monolayer around the metal core. The results open interesting prospects for the development of functionalized metal nanoparticles.