Aims:  The antibiofilm activity of extracts obtained from selected herbs, spices, beverages and commercially important medicinal plants was investigated on Listeria monocytogenes. Methods and Results:  The growth and development of the biofilm was assessed using the crystal violet (CV) assay. The respiratory activity was assessed using the 2, 3‐bis [2‐methyloxy‐4‐nitro‐5‐sulfophenyl]‐2H‐tetrazolium‐5‐carboxanilide (XTT) reduction assay. The majority of extracts tested prevented cell adhesion to the polyvinyl chloride (PVC) surface. Seven of the 15 extracts reduced biofilm adhesion of both the clinical and the type strains by at least 50%. In contrast, inhibition of a preformed biofilm was more difficult to achieve, with only three extracts (Rosmarinus officinalis, Mentha piperita and Melaleuca alternifolia) inhibiting the growth of both strains by at least 50%. Conclusions:  Although most extracts were able to reduce initial cell attachment, inhibition of growth in a preformed biofilm was more difficult to achieve. Significance and Impact of the Study:  The ability to reduce biofilm biomass as shown by several plant extracts warrants further investigation to explore the use of natural products in antibiofilm adhesion.

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Plectranthus ecklonii Benth. is traditionally used in South Africa for treating stomach aches, nausea, vomiting and meningitis. Bioassay-guided fractionation of the ethyl acetate extract of the plant led to the isolation of two known compounds, parvifloron D and parvifloron F, neither of which has been previously reported for this species. The compounds exhibited minimum inhibitory concentrations of 15.6 and 31.2 µg/mL, respectively against Listeria monocytogenes, whereas the values against a drug-sensitive strain of Mycobacterium tuberculosis were 190 and 95 µg/mL, respectively. The ethyl acetate extract of P. ecklonii and its isolated compounds were tested for their activity on tyrosinase inhibition. The concentration at which half the tyrosinase activity was inhibited (IC 50) by the extract was found to be 61.7 ± 2.7 µg/mL. The antibacterial activity of the extract and its isolated compounds correlates with the traditional use of the plant for various ailments such as stomach aches, diarrhea and skin diseases. The fifty percent inhibitory concentrations of parvifloron D and parvifloron F against vero cell lines were found to be 2.9 µg/mL and 1.6 µg/mL, respectively. This is the first report of the bioactivity of P. ecklonii extract and its constituents.

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