Combinatory effect of plant compounds and their derivatives with conventional antibiotics on diarrhoea causing bacteria

Diarrhoeal infections are major cause of morbidity and mortality of children globally [1]. Moreover, emerging antibiotic resistance complicates diarrhoea treatment. Combination of compounds and antibiotics is considered as a new prospective strategy for overcoming bacterial resistance. For example, augmentin (amoxicillin and clavulanic acid) is used to treat certain bacteria-caused diseases such as urinary tract infections. In long time practice, various plant-derived compounds such as berberine sulphate and berberine hydrochloride are useful for diarrhoea control [2]. However, their combinatory effect with conventional antibiotics against diarrhoea causing bacteria has only poorly been investigated.

In this study, we tested in vitro combinations of plant compounds (e.g. berberine chloride, tannic acid and sanguinarine) and their derivatives (e.g. 4, 8-hydroxy-5-nitroquinoline and zinc pyrithione) with selected conventional antibiotics (e.g. ciprofloxacin and tetracycline) against standard strains of diarrheagenic bacteria (e.g. Escherichia coli and Shigella sp.). Minimum inhibitory concentrations of each agent and antibiotics were determined by the broth microdilution method according to Clinical and Laboratory Standards Institute [3] guidelines, whereas the combinatory effect was evaluated according to the sum of fractional inhibitory concentration (ΣFIC) indices obtained by chequerboard method [4].

Several combinations (e.g. sanguinarine with tetracycline) showed additive effects against the majority of bacterial strains tested with ∑FICI ranging from 0.507 to 0.531, whereas the synergistic activity exhibited combination of sanguinarine with ciprofloxacin (∑FICI 0.281 - 0.375) against Vibrio parahaemolyticus and Shigella flexneri.

The results can be used by food and pharmaceutical industries for development of new herbal-based food and pharmaceutical preparations.

• References

• 1 Maroyi A. Treatment of diarrhoea using traditional medicines: Contemporary Research in South Africa and Zimbabwe. Afr J Traditional Complementary Altern Med 2016; 13: 5-10
• 2 Kokoska L, Kloucek P, Leuner O, Plant-Derived NP. Products as Antibacterial and Antifungal Agents in Human Health Care. Curr Med Chem 2019; 26: 1-38
• 3 Clinical and Laboratory Standards Institute. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically, Approved standard M7-A7. 2006. Wayne PA: Clinical and Laboratory Standards Institute;
• 4 European Committee for Antimicrobial Susceptibility Testing (EUCAST). Terminology Relating to Methods for Determination of Susceptibility of Bacteria to Antimicrobial Agents. Clin Microbiol Infect 2000; 6: 503-508