The resistance of commensal 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 production1. 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 antibiotics2. 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 combine with ampicillin, piperacillin, imipenem, vancomycin, gentamicin and aztreonam and the effects were investigate with the chequerboard method. We found 29 combinations that worked synergistically, mainly with ampicillin and gentamicin on the gram positive strains. Five synergistic combinations were found for the first line antibiotics ampicillin (Enterococcus faecium) and piperacillin (Pseudomonas aeruginosa) and two for the last line antibiotic vancomycin (Enterococcus faecium). 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.
[1] World Health Organization. Antimicrobial Resistance Global Report on Surveillance. Geneva: WHO Press; 2014
[2] Abreu AC, McBain AJ, Simões M. Nat Prod Rep 2012; 29(9): 1007-1021