Background Antimicrobial resistance (AMR) remains an important global health issue but the gap between AMR and development of new antimicrobials is increasing. Plant extracts may have good activity per se or may be sources of effective antimicrobial compounds which can act against planktonic and/or biofilms of pathogens. We determined the antimicrobial efficacy and cytotoxicity of some under-investigated plants from the Myrtaceae family endemic to South Africa. The ability of the plant extracts to inhibit or destroy pre-formed bacterial biofilms was also determined. Methods Based on previous preliminary in vitro screening and on chemotaxonomy, nine species from the Myrtaceae family were selected. The antimicrobial activity of the crude acetone leaf extracts was determined against six common nosocomial pathogens, namely: Gram-positive bacteria ( Bacillus cereus , Enterococcus faecalis , Staphylococcus aureus ), Gram-negative bacteria ( Escherichia coli , Pseudomonas aeruginosa , Salmonella Typhimurium) using a two-fold serial microdilution assay with p-iodonitrotetrazolium violet as growth indicator. The number of antimicrobial compounds present in extracts was determined by bioautography. Cytotoxicity of extracts was determined against Vero kidney cells using a colorimetric tetrazolium-based assay. The total antibacterial activity (TAA) in ml/g and selectivity index (LC 50 /MIC) of the plant extracts were calculated. A modified crystal violet assay was used to determine the antibiofilm activity of the extracts. Results Syzygium legatii , Syzygium masukuense , and Syzygium species A had the best activities against Gram-negative and Gram-positive bacteria (MIC) values ranging from 0.04–0.08 mg/ml. Eugenia erythrophylla had the best MIC (0.02 mg/ml) against Bacillus cereus . Many extracts had relatively low cytotoxicity (LC 50 > 20 μg/ml) leading to reasonable selectivity indices. Three leaf extracts ( Syzygium masukuense , Syzygium species A, and Eugenia natalitia ) were moderately cytotoxic (20 μg/ml < LC 50 < 100 μg/ml). The plant extracts had a good capacity to reduce biofilm formation and good to poor potential to destroy pre-formed biofilms. Conclusions The plant species examined in this study had varying degrees of antibacterial activity against bacterial planktonic and biofilm forms with some having good activity against both forms. Several of these selected species may be potential candidates for further investigation to isolate antimicrobial compounds and to determ...

a b s t r a c t Edited by J Van Staden Keywords: Medicinal plants Tuberculosis Mycobacterium CytotoxicityMany plants are used in traditional medicine to treat tuberculosis and other respiratory disorders in Africa. The emergence of multiple drug resistance has become a major threat and thus calls for an urgent need to search for new effective and safe anti-TB agents. The aim was to determine the antimycobacterial activity and the safety of the acetone leaf extracts of 14 plant species used in southern Africa to treat tuberculosis and pulmonary ailments. The antimycobacterial activity was evaluated by a tetrazolium violet based broth microdilution method against three fast-growing mycobacteria species (Mycobacterium smegmatis, Mycobacterium aurum and M. fortuitum) and one pathogenic M. tuberculosis field strain. The in vitro cellular toxicity was determined using the MTT assay on Vero monkey kidney cells. The extraction yield, the LC 50 and MIC values were used to determine the total activity (TA) and the selectivity index (SI) of the extracts. Extracts had moderate to weak activity with the MIC values ranging from 0.039 to N 2.5 mg/mL. M. fortuitum appeared to be better predictor of activity against pathogenic M. tuberculosis than M. smegmatis and M. aurum. Extracts from Heteropyxis natalensis (3.3) and Hexalobus monopetalus (2.47) had the highest selectivity index. The results substantiate the safety and in some cases the potential efficacy of the traditional use of these species against tuberculosis and pulmonary ailments.

BackgroundInfluenza infection is a major public health threat. The role of influenza A virus-induced inflammatory response in severe cases of this disease is widely recognized. Drug resistance and side effects of chemical treatments have been observed, resulting in increased interest in alternative use of herbal medications for prophylaxis against this infection.The South African medicinal plant, Rapanea melanophloeos (RM) (L.) Mez of the family Myrsinaceae was selected owing to its traditional use for the treatment of several diseases such as respiratory ailments and also previous preliminary studies of anti-influenza activity of its methanolic extract. The aim of this study was to investigate the immunomodulatory properties of a glycoside flavone isolated from RM against influenza A virus.MethodsThe non-cytotoxic concentration of the quercetin-3-O-α-L-rhamnopyranoside (Q3R) was determined by MTT assay and tested for activity against influenza A virus (IAV) in simultaneous, pre-penetration and post-penetration combination treatments over 1 h incubation on MDCK cells. The virus titer and viral load targeting NP and M2 viral genes were determined using HA and qPCR, respectively. TNF-α and IL-27 as pro- and anti-inflammatory cytokines were measured at RNA and protein levels by qPCR and ELISA, respectively.ResultsQuercetin-3-O-α-L-rhamnopyranoside at 150 μg/ml decreased the viral titer by 6 logs (p < 0.01) in the simultaneous procedure. The NP and M2 genes copy numbers as viral target genes, calculated based on the Ct values and standard formula, significantly decreased in simultaneous treatment (p < 0.01). The expression of cytokines was also considerably affected by the compound treatment.ConclusionsThis is the first report of quercetin-3-O-α-L-rhamnopyranoside from RM and its immunomodulatory properties against influenza A virus. Further research will focus on detecting the specific mechanism of virus-host interactions.Electronic supplementary materialThe online version of this article (10.1186/s12906-018-2246-1) contains supplementary material, which is available to authorized users.