Antimicrobial and resistance modulatory activity of alpinia katsumadai seed phenolic extract, essential oil and post-distillation extract

Antimicrobial resistance of food-related bacterial pathogens is becoming a serious problem, especially after the emergence of multidrug-resistant strains. To overcome this problem, new and effective antimicrobials or resistance modulators are highly needed and plant kingdom represents a valuable source of these compounds. We investigated antimicrobial and resistance modulatory activity of the phenolic extract, essential oil and post-distillation extract of Alpinia katsumadai seeds against Campylobacter jejuni and Staphylococcus aureus. Among the tested plant formulations, A. katsumadai seed phenolic extract and post-distillation extract showed moderate antimicrobial activity against C. jejuni, while S. aureus was more resistant. When evaluating resistance modulatory potential of A. katsumadai phenolic extract, essential oil and post-distillation extract in C. jejuni against ciprofloxacin, erythromycin, triclosan, bile salts and ethidium bromide, plant formulations exhibited modulatory activity in combination with all antimicrobials. Modulation of resistance was more strain-and antimicrobial-specific in S. aureus, but very efficient in the case of reduced resistance to bile salts. Essential oil from A. katsumadai seeds efficiently increased intracellular ethidium bromide accumulation and was thus confirmed as potential inhibitor of efflux pumps in C. jejuni and S. aureus.