Medicinal plants: bioactive compounds, biological activities, combating multidrug-resistant microorganisms, and human health benefits - a comprehensive review

Abstract

In recent years, medicinal plants have gained significant attention in modern medicine due to their accessibility, affordability, widespread acceptance, and safety, making herbal remedies highly valued globally. Consequently, ensuring medicinal plants' quality, efficacy, and safety has become a critical concern for developed and developing nations. The emergence of multidrug-resistant microorganisms poses a serious global health threat, particularly in low-income regions, despite significant advancements in antimicrobial drugs and medical research over the past century. The rapid spread of these multidrug-resistant infections is primarily attributed to improper prescriptions, overuse, and unregulated access to antibiotics. Addressing these challenges, the standardization of plant-derived pharmaceuticals could pave the way for a transformative era in healthcare. Preserving and leveraging the historical knowledge of medicinal plants is essential before such valuable information is lost. Recently, there has been growing interest among natural and pharmaceutical scientists in exploring medicinal plants as potential sources of antimicrobial agents. This current review aims to identify the most common pathogens threatening human health, analyze the factors contributing to the rise of drug-resistant microorganisms, and evaluate the widespread use of medicinal plants across various countries as alternative antibiotics, highlighting their unique mechanisms of antimicrobial resistance.

Keywords: antibiotics; antimicrobial agents; herbal medicine; human health; mechanism of action; multidrug resistance; pathogens.

Figure 1

The mechanisms of action of several antibiotics on Gram-positive and Gram-negative bacteria. Gram-positive bacteria, characterized by a thick peptidoglycan layer and teichoic acids, are vulnerable to antibiotics such as glycopeptides (e.g., vancomycin) that impede cell wall formation and daptomycin, which affects membrane potential. Gram-negative bacteria, characterized by an outer membrane and a thinner peptidoglycan layer, exhibit lower permeability yet remain susceptible to polymyxins that compromise the outer membrane and other agents that affect ribosomes (protein synthesis) or DNA gyrase (DNA replication). Both types exhibit analogous vulnerabilities in protein synthesis, folic acid metabolism, and DNA replication, which are targeted by antibiotics such as tetracyclines, sulfonamides, and quinolones, respectively. Resistance mechanisms are also demonstrated, including modified penicillin-binding proteins, beta-lactamase synthesis, efflux pumps, and porin alterations.

Figure 2

Antibiotic resistance spread through foods. Animal-derived foods, such as dairy, meat, and poultry, provide the principal source of most foodborne microbial diseases. The improper use of antimicrobial agents in animal feed is the principal factor contributing to the increasing public health issue about multi-drug resistant (MDR) microorganisms in these foods. The application of antibiotics in agriculture, livestock production, and human healthcare exerts selection pressure on genes that impart antibiotic resistance. The over-application of antibiotics in animal farming as growth promoters significantly contributes to the development and proliferation of antibiotic resistance. MDR microorganisms, antibiotic residues, and resistance genes can enter agricultural soils via sewage sludge and animal manure, ultimately infiltrating the crop microbiome and the human food chain. Ingesting food can transmit these resistance genes into the human microbiome, posing a significant public health threat.

Figure 3

Main factors leading to antibiotic resistance.

Figure 4

Primary and secondary metabolites of medicinal plants.

Figure 5

Antibacterial mechanism of medicinal plants against multi-drug resistance (MDR) as natural alternatives to antibiotics.