Natural products as modifiers of antibiotic resistance

The resistance of bacteria to first and second line antibiotics has reached an alarming level in many parts of the world and endangers the effective treatment of infectious diseases. It is a complex global public health challenge that leads to prolonged illness and increased mortality, increases the costs for the health-care sector, and has an impact on animal health, which also could lead to an effect on food production [1]. The development of resistance-modifying agents (RMAs) can mitigate the spread of bacterial drug resistance and possibly extend the useful life of an antibiotic, importantly in consideration of the lack of new antibiotics [2]. We investigated the activity of nine methanolic extracts of plants, which were used traditionally to cure wounds, and some single substances as an RMA of multi-resistant clinical isolates of Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus (MRSA) and Enterococcus faecium (VRE) which can be involved in wound infections. The extracts and single substances were combined with ampicillin, piperacillin, imipenem, vancomycin, gentamicin and aztreonam and the effects were investigated with the chequerboard method. We found 29 combinations that worked synergistically, mainly with ampicillin and gentamicin on the gram positive strains. The highest diminishment of antibiotic resistance shows the extract of Cetraria islandica with gentamicin (MIC shift: 16 to 0.001953125 µg/mL), extract of Salvia officinalis with vancomycin (MIC shift: 256 to ≤0.015625 µg/mL) and glycyrrhizic acid with gentamicin (MIC shift: 131072 to between 8 and 16 µg/mL, high-level resistant isolates) on Enterococcus faecium.

• References

• 1 World Health Organization. Antimicrobial Resistance Global Report on Surveillance. Geneva: WHO Press; 2014
• 2 Abreu AC, McBain AJ, Simões M. Plants as sources of new antimicrobials and resistance-modifying agents. Nat Prod Rep 2012; 29 (09) : 1007-1021