Tea (Camellia sinensis) is one of the most popular nonalcoholic beverages, consumed by over two-thirds of the world's population because of its refreshing, mild stimulant and medicinal properties. It is processed in different ways in different parts of the world to give green, black, oolong, and pu-erh tea. Among all tea polyphenols, epigallocatechin-3-gallate has been responsible for much of the health promoting abilities of tea including anti-inflammatory, antimicrobial, antitumour, anti-oxidative, protection from cardiovascular disease, anti-obesity, and anti-aging properties. In the present review, the antibacterial, antiviral, and antifungal activities of different types of tea and their polyphenols are reported, highlighting their mechanisms of action and structure-activity relationship. Moreover, considering that the changing patterns of infectious diseases and the emergence of microbial strains resistant to current antibiotics, there is an urgent need to find out new potent antimicrobial agents as adjuvants to antibiotic therapy. The synergistic effect of tea polyphenols in combination with conventional antimicrobial agents against clinical multidrug-resistant microorganisms has also been discussed in this review.

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The ongoing pandemic of global concern has killed about three million humans and affected around 151 million people worldwide, as of April 30, 2021. Although recently approved vaccines for COVID-19 are engendering hope, finding new ways to cure the viral pandemic is still a quest for researchers worldwide. Major pandemics in history have been of viral origin, such as SARS, MERS, H1NI, Spanish flu, and so on. A larger emphasis has been on discovering potential vaccines, novel antiviral drugs, and agents that can mitigate the viral infection symptoms; however, a relatively new area, RNA interference (RNAi), has proven effective as an antiviral agent. The RNAi phenomenon has been largely exploited to cure cancer, neurodegenerative diseases, and some rare diseases. The U.S. Food and Drug Administration has recently approved three siRNA products for human use that garner significant hope in siRNA therapeutics for coronaviruses. There have been some commentaries and communications addressing this area. We have summarized and illustrated the significance and the potential of the siRNA therapeutics available as of April 30, 2021 to combat the ongoing viral pandemic and the emerging new variants such as B.1.1.7 and B.1.351. Numerous successful in vitro studies and several investigations to address the clinical application of siRNA therapeutics provide great hope in this field. This seminal Review describes the significance of siRNA-based therapy to treat diverse viral infections in addition to the current coronavirus challenge. In addition, we have thoroughly reviewed the patents approved for coronaviruses, the major challenges in siRNA therapy, and the potential approaches to address them, followed by innovation and prospects.

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We describe the design and synthesis of a new series of non-natural short cationic lipopeptides (MW = 700) as antimicrobial agents. All of the synthesized lipopeptides were tested against a range of microbes such as Gram-positive, Gram-negative bacteria, fungi including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). By systematic study of design template, we found that three ornithine residues conjugated with myristic acid are minimum requirement for a compound to be an antimicrobial agent. The most potent lipopeptide LP16 possesses broad-spectrum antimicrobial activity and has MICs in the range of 1.5-6.25 μg/mL against Escherichia coli, S. aureus, Pseudomonas aeruginosa, Bacillus subtilis, and MRSE. All lipopeptides showed high selectivity toward microbial strains as compared to human red blood cells (HC50 > 250 μg/mL). Moreover, most potent lipopeptides (LP16 and LP23) did not induce drug resistance in S. aureus even after 15 rounds of passaging. In addition, a representative lipopeptide (LP16) showed tryptic stability for 24 h. These results suggest the potential of short cationic lipopeptides to boost the discovery of future antimicrobial therapeutics.

We report the synthesis and antibacterial activities of a series of amphiphilic membrane-active peptides composed, in part, of various nongenetically coded hydrophobic amino acids. The lead cyclic peptides, 8C and 9C, showed broad-spectrum activity against drug-resistant Gram-positive (minimum inhibitory concentration (MIC) = 1.5−6.2 μg/mL) and Gram-negative (MIC = 12.5−25 μg/ mL) bacteria. The cytotoxicity study showed the predominant lethal action of the peptides against bacteria as compared with mammalian cells. A plasma stability study revealed approximately 2-fold higher stability of lead cyclic peptides as compared to their linear counterparts after 24 h of incubation. A calcein dye leakage experiment revealed the membranolytic effect of the cyclic peptides. Nuclear magnetic resonance spectroscopy and molecular dynamics simulation studies of the interaction of the peptides with the phospholipid bilayer provided a solid structural basis to explain the membranolytic action of the peptides with atomistic details. These results highlight the potential of newly designed amphiphilic peptides as the next generation of peptide-based antibiotics.

Resistant pathogenic microbial strains are emerging at a rate that far exceeds the pace of new anti-infective drug development. In order to combat resistance development, there is pressing need to develop novel class of antibiotics having different mechanism of action in comparison to existing antibiotics. Antimicrobial peptides (AMPs) have been identified as ubiquitous components of innate immune system and widely regarded as a potential source of future antibiotics owing to a remarkable set of advantageous properties ranging from broad spectrum of activity to low propensity of resistance development. However, AMPs present several drawbacks that strongly limit their clinical applicability as ideal drug candidates such as; poor bioavailability, potential immunogenicity and high production cost. Thus, to overcome the limitations of native peptides, peptidomimetic becomes an important and promising approach. The different research groups worldwide engaged in antimicrobial drug discovery over the past decade have paid tremendous effort to design peptidomimetics. This review will focus on recent approaches in design of antimicrobial peptidomimetics their structure-activity relationship studies, mode of action, selectivity & toxicity.