Tabebuia impetiginosa (Mart. Ex DC. Mattos) Bark Extracts Inhibit the Growth Gastrointestinal Bacterial Pathogens and Potentiate the Activity of some Conventional Antibiotics

Introduction: Tabebuia impetiginosa (Mart. Ex DC. Mattos) bark has been used to treat inflammation and cancer, as well as a variety of pathogenic diseases, in traditional South American healing systems. As practitioners of complementary medicine frequently use herbal medicines concurrently with conventional antibiotics, the effects of both therapies in combination needs to be evaluated. Methods: The growth inhibitory activity of T. impetiginosa bark extracts was assessed against a panel of gastrointestinal bacterial pathogens by standard disc diffusion and liquid dilution minimum inhibitory concentration (MIC) methods. Combinational effects between the extracts and conventional antimicrobials were classified using the sum of the fractional inhibitory concentration. The toxicity of the individual samples and combinations was evaluated by Artemia lethality and MTS HDF cell viability assays. Results: T. impetiginosa bark extracts strongly inhibited the growth of B. cereus but were ineffective against Escherichia coli, Shigella sonnei, Staphylococcus aureus. The mid polarity ethyl acetate extract was a particularly good inhibitor of B. cereus growth (DD and LD MIC values of 45 and 245 μg/mL respectively). However, the effects of combinations of the extracts and conventional antibiotics was of considerably more interest. Although no synergistic interactions were noted, the potency of some combinations were substantially potentiated compared to activity of the individual components. Additive potentiation was was noted for combinations containing the T. impetiginosa water extract and erythromycin, chloramphenicol or penicillin-G against E. coli and S. aureus. Combinations containing ciprofloxacin also produced additive effects against all of the bacteria tested. Therefore, these combinations have enhanced benefits over either component alone. Of further note, antagonistic interactions were also detected in several combinations containing ciprofloxacin (particularly against S. aureus). These combinations should therefore be avoided against that bacterium. Conclusion: T. impetiginosa bark extracts inhibit the growth of B. cereus when tested alone and potentiated the activity of some conventional antibiotics against a panel of gastrointestinal pathogens when used in combination. Thus, T. impetiginosa bark extracts have potential in the treatment of diarrhoea and other gastrointestinal diseases.