Validation of a traditional preparation against multi-drug resistant Salmonella Typhi and its protective efficacy in S. Typhimurium infected mice

Shorea robusta Gaertn has been used for skin and intestinal ailments in Indian Traditional medicine; while two tribal communities used its tender leaves in 'Meyadi-bukhar' or long-term fever. This prompted us to validate the aqueous and methanol extracts of Shorea robusta tender leaves against wild-and multidrug-resistant clinical isolates of Salmonella enterica Serovar Typhi (S. Typhi), the causative agent of typhoid fever. The antibacterial activity, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and growth inhibition were determined using disc diffusion, agar-and-broth dilution, dose-and time-response assays, along with the safety and protective efficacy in Balb/C mice, infected with S. Typhimurium. The MIC of the extract was 256-450 mu g/ml against S. Typhi isolates, and 700 mu g/ml for mouse virulent S. Typhimurium, while MBC was <= 512-1024 mu g/ml. The growth curve revealed that the extract was bactericidal at 4-6 h of exposure. Toxicity study showed that the extract was safe up to 3000 mg/kg (p.o.). Moreover, it significantly (p > 0.01) protect the challenged (1.4x10(8) cfu/ml) mice at 93.75 (i.p.) and 300 mg/kg (p.o.) dose, compared to the infection control (distilled water treatment group). Collectively, our results confirmed the antibacterial potential of the test extracts against MDR-isolates of S. Typhi.