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In the search for alternative treatment options for infections with multi-resistant germs, traditionally used medicinal plants are currently being examined more intensively. In this study, the antimicrobial and anti-biofilm activities of 14 herbal drugs were investigated. Nine of the tested drugs were traditionally used in Europe for treatment of local infections. For comparison, another five drugs monographed in the European Pharmacopoeia were used. Additionally, the total tannin and flavonoid contents of all tested drugs were analyzed. HPLC fingerprints were recorded to obtain further insights into the components of the extracts. The aim of the study was to identify herbal drugs that might be useable for treatment of infectious diseases, even with multidrug resistant E. coli, and to correlate the antimicrobial activity with the total content of tannins and flavonoids. The agar diffusion test and anti-biofilm assay were used to evaluate the antimicrobial potential of different extracts from the plants. Colorimetric methods (from European Pharmacopeia) were used for determination of total tannins and flavonoids. The direct antimicrobial activity of most of the tested extracts was low to moderate. The anti-biofilm activity was found to be down to 10 µg mL−1 for some extracts. Tannin contents between 2.2% and 10.4% of dry weight and total flavonoid contents between 0.1% and 1.6% were found. Correlation analysis indicates that the antimicrobial and the anti-biofilm activity is significantly (p < 0.05) dependent on tannin content, but not on flavonoid content. The data analysis revealed that tannin-rich herbal drugs inhibit pathogens in different ways. Thus, some of the tested herbal drugs might be useable for local infections with multi-resistant biofilm-forming pathogens. For some of the tested drugs, this is the first report about anti-biofilm activity, as well as total tannin and flavonoid content.
Background
In addition to the broad dissemination of pathogenic extended-spectrum beta-lactamase (ESBL)-producing Escherichia (E.) coli in human and veterinary medicine and the community, their occurrence in wildlife and the environment is a growing concern. Wild birds in particular often carry clinically relevant ESBL-producing E. coli.
Objectives
We analyzed ESBL-producing and non-ESBL-producing E. coli obtained from wild birds in Mongolia to identify phylogenetic and functional characteristics that would explain the predominance of a particular E. coli clonal lineage in this area.
Methods
We investigated ESBL-producing E. coli using whole-genome sequencing and phylogenetics to describe the population structure, resistance and virulence features and performed phenotypic experiments like biofilm formation and adhesion to epithelial cells. We compared the phenotypic characteristics to non-ESBL-producing E. coli from the same background (Mongolian wild birds) and genomic results to publicly available genomes.
Results and Conclusion
We found ESBL-producing E. coli sequence type (ST) 1159 among wild birds in Mongolia. This clonal lineage carried virulence features typical for extra-intestinal pathogenic or enterotoxigenic E. coli. Comparative functional experiments suggested no burden of resistance in the ST1159 isolates, which is despite their carriage of ESBL-plasmids. Wild birds will likely disseminate these antibiotic-resistant pathogens further during migration.
The study aimed to examine the influence of a rotating magnetic field (RMF) of two different frequencies (5 and 50 Hz) on the expression of regulatory (agrA, hld, rot) and staphylococcal enterotoxin (SE—sea, sec, sel) genes as well as the production of SEs (SEA, SEC, SEL) by the Staphylococcus aureus FRI913 strain cultured on a medium supplemented with a subinhibitory concentration of trans-anethole (TA). Furthermore, a theoretical model of interactions between the bacterial medium and bacterial cells exposed to RMF was proposed. Gene expression and SEs production were measured using quantitative real-time PCR and ELISA techniques, respectively. Based on the obtained results, it was found that there were no significant differences in the expression of regulatory and SE genes in bacteria simultaneously cultured on a medium supplemented with TA and exposed to RMF at the same time in comparison to the control (unexposed to TA and RMF). In contrast, when the bacteria were cultured on a medium supplemented with TA but were not exposed to RMF or when they were exposed to RMF of 50 Hz (but not to TA), a significant increase in agrA and sea transcripts as compared to the unexposed control was found. Moreover, the decreased level of sec transcripts in bacteria cultured without TA but exposed to RMF of 50 Hz was also revealed. In turn, a significant increase in SEA and decrease in SEC and SEL production was observed in bacteria cultured on a medium supplemented with TA and simultaneously exposed to RMFs. It can be concluded, that depending on SE and regulatory genes expression as well as production of SEs, the effect exerted by the RMF and TA may be positive (i.e., manifests as the increase in SEs and/or regulatory gene expression of SEs production) or negative (i.e., manifests as the reduction in both aforementioned features) or none.
Abstract
Aim
To verify synergistic effects, we investigated the antimicrobial activity of seven phenolic phytochemicals (gallic acid; epicatechin; epigallocatechin gallate; daidzein; genistein; myricetin; 3‐hydroxy‐6‐methoxyflavone) in combination with six antibiotics against multidrug‐resistant isolates from the ESKAPE group.
Methods and Results
To investigate single phytochemicals and combinations, initial microdilution and checkerboard assays were used, followed by time‐kill assays to evaluate the obtained results. The research revealed that phenolic compounds on their own resulted in little or no inhibitory effects. During preliminary tests, most of the combinations resulted in indifference (134 [71.3%]). In all, 30 combinations led to antagonism (15.9%); however, 24 showed synergistic effects (12.8%). The main tests resulted in nine synergistic combinations for the treatment of four different bacteria strains, including two substances (3‐hydroxy‐6‐methoxyflavone, genistein) never tested before in such setup. Time‐kill curves for combinations with possible synergistic effects confirmed the results against Acinetobacter baumannii as the one with the greatest need for research.
Conclusions
The results highlight the potential use of antibiotic–phytocompound combinations for combating infections with multi‐resistant pathogens. Synergistic combinations could downregulate the resistance mechanisms of bacteria.
Significance and Impact of the Study
The aim of this study is to demonstrate the potential use of phenolic natural compounds in combination with conventional antibiotics against multidrug‐resistant bacteria of the ESKAPE group. Due to synergistic effects of natural phenolic compounds combined with antibiotics, pathogens that are already resistant to antibiotics could be resensitized as we were able to reduce their MICs back to sensitive. In addition, combination therapies could prevent the development of resistance by reducing the dose of antibiotics. This approach opens up the basis for future development of antimicrobial therapy strategies, which are so urgently needed in the age of multidrug‐resistant pathogens.