Attention to these issues could accompany in a poorly needed new era of chemotherapeutic treatment of infection by using plant derived principles. This review outline the main methods used in the evaluation of antimicrobial activity of plant extracts; each method has advantages and limitations and all have been widely cited in the literature. The question of which is the best one to use is essentially unanswerable as preferred methods depend on a variety factors including access to specialized equipment and facilities, the number of samples to be screened and the nature of the plant extract (e.g. volume, extract versus essential oil, chemical composition). For large-scale screening of extracts for antibacterial and antifungal activity disk and agar diffusion methods offer a fast, cost effective, low tech, and generally reliable method of sorting those extracts worthy of further investigation from those unlikely to be of value.

Broth dilution methods provide more information but are more time and labour intensive and are best used as a follow up to a large scale screening of plant extracts. Antiviral and antiparasitic assays are the most time and labour intensive of the in vitro antimicrobial testing methods and often require access to cell culture or other specialized laboratory facilities. These are used less frequently than antibacterial and antifungal assays. Despite the limitations of many of the assay techniques, there is a vast amount of good data demonstrating that some plant extracts possess strong to excellent antimicrobial activity. The next step is to continue this work into the in vivo environment and to evaluate the activity of these extracts in the treatment of infectious disease.