Phytoshield: A Systematic Review (PRISMA 2020) of Emerging Antimicrobial Plants Targeting Multidrug-Resistant Pathogens

Abstract

Multidrug-Resistant (MDR) bacterial infections are increasingly difficult to treat and represent a major global health concern. Consequently, medicinal plants are being explored as potential sources of novel antimicrobial agents. Plant-derived phytochemicals often display diverse biological activities and may target bacterial physiology through multiple mechanisms. This review evaluates contemporary evidence describing plant-based antibacterial activity against MDR pathogens. To identify medicinal plants and phytochemical constituents reported to exhibit activity against MDR bacteria and to summarize their antimicrobial potency and proposed mechanisms of action. A systematic review was conducted according to the PRISMA 2020 guidelines, from the relevant literature published between 2021 and 2025. A total of 1,238 records were retrieved from databases, of which 494 studies underwent full-text assessment and 21 published studies met the eligibility requirements for this review. The information collected from the studies included: the botanical species used, the method of preparation, the MDR pathogen tested, the Minimum Inhibitory Concentration (MIC), the Minimum Bactericidal Concentration (MBC), and the mechanism of action as determined by the authors of the publication. A total of 40 medicinal plant collections from different families were evaluated. Frequently represented plant families included Zingiberaceae, Lamiaceae, Fabaceae, Lauraceae, and Myrtaceae. Antibacterial activity was most commonly reported against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Isolated phytochemicals generally demonstrated lower MIC values than crude extracts. Major compound classes included flavonoids, tannins, terpenoids, alkaloids, and essential-oil constituents, with reported mechanisms involving membrane perturbation, antibiofilm activity, efflux modulation, and potential enhancement of antibiotic efficacy. This review shows that phytochemicals from medicinal plants are very effective against bacteria that are resistant to Multiple Drugs (MDR). These substances work by directly killing bacteria and improving the effectiveness of antibiotics, especially against WHO priority pathogens like P. aeruginosa, E. coli, K. pneumoniae, A. baumannii, and S. aureus. Alkaloids, flavonoids, tannins, and terpenoids are the main active groups. They work in more than one way, such as breaking down membranes, stopping biofilms from forming, stopping efflux pumps, and lowering virulence. This may slow down the development of resistance. Allicin, thymoquinone, and cinnamaldehyde are very active (low MIC), while curcumin and EGCG have moderate but synergistic effects. Essential-oil components frequently exhibit greater potency than crude extracts. Phytochemicals show promise as adjuncts in combination therapy, though standardization and additional molecular validation are necessary. Medicinal plants provide a valuable reservoir of bioactive molecules with experimentally demonstrated activity against MDR pathogens. However, variation in experimental methodology and limited translational validation indicate that further standardized and mechanistically focused investigations are required before clinical application can be considered.