Microbial infections and antibiotic resistance are two of the most serious threats to society's health today. Millions of people die each year as a result of microbial infections. In 2020, the COVID-19 pandemic caused by viral infections was responsible for the highest amount of all deaths that year. Existing antimicrobial drugs have become less effective, if not ineffective, as a result of the emergence of resistance. Several antibiotic resistance-fighting strategies have been proposed in recent years. One strategy proposed to achieve this objective has been to use combination therapy which appears to restore the desired antimicrobial activity. Several medicinal plants have demonstrated therapeutic effects against pathogens that cause human infections due to their phytochemicals constituents which have been elucidated to act as antimicrobial agents. This chapter focuses on phytochemicals as antimicrobial agents, giving information about infectious diseases and the pathobiology of these diseases. Also, the mechanisms of antimicrobial activity of phytochemical were discussed.
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Over the last million years, human population growth has been adversely affected by the emergence of highly contagious and virulent diseases (McMichae, 2004), which has had a global impact on the environment. Agriculture contributed to this as well, because these highly contagious diseases could only be continuous in huge and densely populated regions (Wolfe et al., 2007). Discovery of antibiotics coupled with substantialdevelopments in antimicrobial therapeutics has enhanced human wellbeing and health by improving infection management and/or treatment (Aminov, 2010). However, prolonged antibiotic use resulted in bacterial adaptation and could also lead to multidrug resistance (Tenover, 2006). Antibiotic efficacy has been significantly reduced due to multidrug resistance, as a result, necessitating a quest for substitute antimicrobial treatment strategies.
Most infections and illnesses are caused by the pertinaciousness of bacteria in alocation and their interaction with humans. Bacterial infections are facilitated by a variety of virulence factors that facilitate various aspects of their pathophysiology that are critical for disease in the host (Falkow, 1991). Membrane proteins and adhesins, for example, facilitate bacterial colonization, attachment, and invasion of host cells. Furthermore, microbial toxins cause tissue damage in the host, and bacterial cell wall machineriessuch as capsular polysaccharides impart resistance to the host immune system (Taylor & Roberts, 2005). Spore formation and biofilm developing ability are two further virulence features that aid pathogen persistence in severe environmental circumstances.
Medicinal plants have performed important functions in the well-being and development of human evolution since ancient times. To maintain human health and prevent food spoilage, a variety of plant products including spices have been utilized as dietary supplements, flavor enhancers, and food preservatives. Furthermore, products of plant origin have been widely utilized in herbal and traditional medicine for disease control, both prophylactically and therapeutically. Several plant-derived compounds have been shown to have antimicrobial activity (Burt, 2004), and a diverse range of active components have been identified (Dixon, 2001). The majority of these compounds are secondary metabolites produced by joint interactions between animals, microbes, and plants (Reichling, 2010). These substances do not seem to have orchestrated impact on the physiology of the plant (Jones & Dangl, 2006), but they are important for improving protection against attacksand enhance plant fitness (Stamp, 2003). Secondary metabolite production is frequently constrained to a small number of species within a phylogenetic group, as opposed to primary metabolites (lipids, proteins, polysaccharides, and amino acids), which are found throughout the plant kingdom (Hashemi & Davoodi, 2012). Furthermore, they are only produced at micro- to submicromolar concentrations during a specific developmental period of plant growth (Hashemi & Davoodi, 2012).