Antibacterial and antibiotic-modulation activity of six Cameroonian medicinal plants against Gram-negative multi-drug resistant phenotypes

BACKGROUND: Bacterial Infections involving multi-drug resistant (MDR) phenotypes constitute a worldwide health concern. The present work was designed to assess the antibacterial properties of the methanol extracts of six medicinal plants (Anthocleista schweinfurthii, Nauclea latifolia, Boehmeria platyphylla, Caucalis melanantha, Erigeron floribundus and Zehneria scobra) and the effects of their associations with antibiotics on MDR Gram-negative bacteria over-expressing active efflux pumps. METHODS: The antibacterial activities and the ability to potentiate antibiotic effects of the methanol extracts the tested plants were evaluated in vitro against twenty eight Gram-negative bacteria expressing MDR phenotypes, using broth microdilution method. The phytochemical screening of these extracts was also performed using standard methods. RESULTS: All tested extracts displayed moderate to low antibacterial activity on at least 14.3 % of the 28 tested bacteria, with MIC values ranged from 128 to 1024 μg/mL. The best antibacterial spectrum was observed with Naulcea latifolia bark extract. Extracts from A. schweinfurthii fruits, N. latifolia stem bark, Z. scobra and N. latifolia leaves showed synergistic effects with many antibiotics against MDR bacteria. CONCLUSION: The overall results of the present study provide information for the possible use of the studied plants, especially Nauclea latifolia in the control of Gram-negative bacterial infections including MDR species as antibacterials as well as resistance modulators. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12906-016-1105-1) contains supplementary material, which is available to authorized users.