Anti-microbial Activity of Aqueous Quercus infectoria Gall Extract against Pathogenic Leptospira

BACKGROUND: Quercus infectoria gall extract is known to have broad spectrum anti-microbial activity in vitro. This study was conducted to determine the anti-microbial activity of Q. infectoria gall extract against pathogenic Leptospira and to evaluate the morphological changes of extract-treated cells using a scanning electron microscope (SEM). METHODS: A two-fold serial microdilution broth assay was used to determine the minimum inhibitory concentration (MIC) of aqueous Q. infectoria gall extract against the L. interrogans serovar Javanica and the L. interrogans serovar Icterohaemorrhagiae, at concentrations ranging from 4.00 mg/mL to 0.0078 mg/mL. The minimum bactericidal concentration (MBC) was determined by sub-culturing the broth from the microtiter plate wells that showed no apparent growth or turbidity to the freshly prepared Ellinghausen-McCullough-Johnson-Harris (EMJH) broth media, and it was subsequently observed under a dark field microscope following three weeks of incubation for purposes of growth detection. The cell morphology of both extract-treated and untreated L. interrogans serovar Icterohaemorhagiae was analysed using the SEM. RESULTS: The results of the broth microdilution assay demonstrate that the aqueous Q. infectoria gall extract possesses anti-microbial activity against both of the L. interrogans serovars with MIC values of 0.125 mg/mL. The MBC values for the L. interrogans serovar Javanica and the L. interrogans serovar Icterohaemorhagiae are 0.125 mg/mL and 0.250 mg/mL, respectively. The SEM micrograph shows changes in shape and size of the extract-treated cells (at 8× MIC) in comparison to the untreated cells. CONCLUSION: The Q. infectoria gall extract displays anti-microbial inhibition and killing activity against the pathogenic Leptospira isolates, and thus has the potential for further exploration of its efficacy and use in the treatment of leptospirosis.