To test whether neem extract and azadirachtin inhibit soil microorganisms, serial dilutions of soil suspensions were made, and suitable dilutions were used to inoculate poured plates of NA and PDA media, which were mixed with the extract or azadirachtin to concentrations at 0.1 and 0.4 gmL-1 of the neem extract or 1.25 and 2.5 µgmL-1 of azadirachtin. These concentrations were chosen based on a report by Aliero (2003) and Ali et al. (2010), who stated that 0.1 and 0.4 gmL-1 extracts could be used to control mosquito larvae and aphids, respectively. The 1.25 and 2.5 µgmL-1 azadirachtin concentrations are those recommended by Thai Neem Products CO., LTD. for agricultural pest control. After incubation at 30 °C for 1 day, the colony-forming units (CFU) on the NA and PDA plates were counted.