Sanitisation effects of selected medicinal plant extracts against Escherichia coliO157:H7 and Salmonella enterica subsp.enterica(Serovar Typhi) on Malus pumila Mill. fruit surfaces

Abstract

Raw fruit and vegetables have become a major risk factor for diarrhoea outbreaks across the world. Salmonella enterica and Shiga toxin-producing Escherichia coli account for 21% and 10% of all diarrhoeal outbreaks around the globe. Despite these statistics, the quantitative risk of consuming RTEFV remains unknown. The potential utility of medicinal plant extracts as disinfectants of RTEFV has remained unexplored. This study sought to assess the efficacy of extracts of Vernonia amygdalina and Ximenia caffra in the removal of Salmonella typhi and E. coli on Malus pumilaMill. fruit surfaces. Two-cm2 square sections of apple epidermal tissues from apples spiked with S. typhi and E. coli were soaked in prepared extracts for 90 minutes. Microbial loads on washed surfaces were determined using conventional agar plate based techniques. Washing of apple surfaces with ethanolic extracts of freshly crushed leaves of X. caffra (X-FLEE) and dry leaves of V. amygdalina (V-DLEE) achieved at least 7 log reductions in counts of E. coli and S. typhi without changes in surface morphology and colour. The selected extracts were shown to be rich in alkaloids, tannins and flavonoids, which are known to harbour antimicrobial activities (inhibitory and cidal effects). Extracts from the selected plants, especially ethanolic extracts of X. caffra and V. amygdalina have potential as sanitisers of apples against diarrhoeagenic E. coli and S. typhi. We therefore recommend the use of ethanol as a solvent of choice in obtaining plant extracts for use-, as well as the use of as well as vinegar, chlorinated water or bicarbonate of soda as sanitisers of fresh apple surfaces.