Antibacterial efficacies and time-kill kinetics of indigenous Ghanaian spice extracts against Listeria monocytogenes and some other food-borne pathogenic bacteria

Abstract

Increase in food-borne outbreaks has become public health concern worldwide. Exploitation of the antimicrobial properties of dietary spices has become important pharmaceutical tool for controlling food-borne pathogens. This study aimed at evaluating the antibacterial potentials of Ghanaian spices against Listeria monocytogenes and other prevalent food-borne pathogens. In preliminary studies, Listeria was isolated from some food samples. The overall prevalence of Listeria spp. was 23% (13/56). Of the 56 samples examined, 7% showed pathogenic potential for L. monocytogenes. Different solvent extracts of thirteen spices namely Calabash nutmeg, West African black pepper, Aidan, Grains of paradise, Negro pepper, Aniseed, African locust bean, Cinnamon, Black pepper, Clove, Cayenne, Basil, and Rauvolfia were tested for their potentials to inhibit clinical and isolated strains of L. monocytogenes using qualitative and quantitative antimicrobial assay methods. Only clove and negro pepper among the thirteen different solvent extracts showed bacteriostatic and bactericidal activity against L. monocytogenes indicated by minimum inhibitory concentrations ranging from 0.05% to 0.4% and minimum bactericidal concentrations ranging from 0.1% to > 0.4% under experimental conditions. Time-kill study demonstrated listericidal activity of ethanolic clove and negro pepper extracts indicated by absolute mortality of more than 3 log units at 2x MIC and 4x MIC. GC-MS analysis revealed three and eight major chemical components present in clove and negro pepper respectively. Staphylococcus aureus, methicillin-resistant S. aureus, Bacillus cereus, and B. subtilis also showed satisfactory susceptibilities to ethanolic extracts with MIC ranging from 0.025% to > 0.8%. In general, negro pepper showed broad activity eliciting inhibitory effects against all the tested pathogens. The findings suggest that clove and negro pepper may be promising antibacterial candidates for the decontamination and control bacterial pathogens in food and food supply chain.

Keywords: Antibacterial activity; Dietary spices; GC-MS; Ghana; L. monocytogenes; Time-kill kinetics.