The potential of aqueous and acetone extracts of galls of Quercus infectoria   as antibacterial agents

OBJECTIVE: To evaluate the antibacterial potential of aqueous and acetone extracts of galls of Quercus infectoria by determination of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values. MATERIALS AND METHODS: The extracts from the galls of Q. infectoria at 10 mg/ml were screened against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis and Bacillus subtilis ) and three Gram-negative bacteria (Escherichia coli NCTC 12079 serotype O157:H7, Salmonella typhimurium NCTC 74 and Pseudomonas aeruginosa ATCC 27853). The MIC of the extracts were then determined using the twofold serial microdilution technique at a concentration ranging from 5 mg/ml to 0.0024 mg/ml. The MBC values were finally obtained from the MIC microtiter wells which showed no turbidity after 24 hrs of incubation by subculturing method. RESULTS: Out of the six bacterial species tested, S. aureus was the most susceptible. On the other hand, the extracts showed weak inhibitory effect against S. epidermidis, B. subtilis, S. typhimurium and P. aeruginosa while there was no inhibition zone observed for E. coli O157. The MIC values of the extracts ranged from 0.0781 mg/ml to 1.25 mg/ml whereas the MBC values ranged from 0.3125 mg/ml to 2.50 mg/ml. The MBC values of aqueous extract against S. aureus and S. typhimurium were higher than their MIC values. The MBC value of acetone extract against S. aureus was also higher than its MIC value. Interestingly, however, the MIC and MBC values of acetone extract against S. typhimurium were the same (1.25 mg/ml). CONCLUSION: The aqueous and acetone extracts displayed similarities in their antimicrobial activity on the bacterial species and as such, the galls of Quercus infectoria are potentially good source of antimicrobial agents.