Phytochemical activity against drug-resistant microbes: Current status and future prospects

The advance of antimicrobial resistance to existing frontline therapeutics is widely recognized as a global health threat. In order to address the increasing challenge that this presents to patient treatment by the medical profession pharmaceutical and biotechnology sectors continue to seek novel therapeutic agents to which pathogens, notably bacteria, are sensitive. The discovery of antibiotics in the last century led to a rapid and profound reduction in morbidity and mortality associated with commonly occurring bacterial diseases. However, the ongoing heavy reliance and indiscriminate use has resulted, due to genetic mutation under selective pressure, in the emergence of antibiotic-resistant bacteria. In searching for new commercial sources of antimicrobials crude extracts of medicinal plants have attracted attention. The wide range of metabolites – for example, alkaloids, tannins and polyphenols – carry therapeutic potential as either novel antimicrobials or modifiers of existing resistance. Plant extracts containing such phytochemicals are able to bind to protein domains, thereby modifying or inhibiting protein-protein interactions. This enables these herbal derivatives to act as effective modulators of cellular metabolic pathways involved in the immune response, mitosis, apoptosis and signal transduction. Hence, the mechanism(s) of action may not necessarily be directly microbicidal but instead affect key events within the host cell that reduce the ability of bacteria, fungi and viruses to thrive in an intracellular environment. In this chapter, a brief history of antibiotics and the spread of resistance is provided. We describe phytochemicals that are currently known and outline their antimicrobial activities. Future strategies to combat drug-resistant microbes are discussed.