Medicinal plants for the prevention and treatment of bacterial infections

Infectious diseases are a significant cause of morbidity and mortality worldwide, accounting for approximately 50% of all deaths in tropical countries and as much as 20% of deaths in the Americas. Despite the significant progress made in microbiology and the control of microorganisms, sporadic incidents of epidemics due to drug resistant microorganisms and hitherto unknown disease-causing microbes pose an enormous threat to public health. These negative health trends call for a global initiative for the development of new strategies for the prevention and treatment of infectious disease. For over 100 years chemical compounds isolated from medicinal plants have served as the models for many clinically proven drugs, and are now being re-assessed as antimicrobial agents. The reasons for this renaissance include a reduction in the new antibacterial drugs in the pharmaceutical pipeline, an increase in antimicrobial resistance, and the need of treatments for new emerging pathogens. Literally thousands of plant species have been tested against hundreds of bacterial strains in vitro and many medicinal plants are active against a wide range of gram positive and gram negative bacteria. However, very few of these medicinal plant extracts have been tested in animal or human studies to determine safety and efficacy. This review focuses on the medicinal plants and bacteria for which there is significant published in vitro, in vivo and clinical data available. The examples provided in this review indicate that medicinal plants offer significant potential for the development of novel antibacterial therapies and adjunct treatments (i.e. MDR pump inhibitors).