Original Pan XX Antibacterial Technology Circle
First author: Lisa M. Stabryla
Component author: Leanne M. Gilbertson
Communication unit: University of Pittsburgh
Research quick look
Recently, Leanne M. Gilbertson's research team at Nature Nanotechnology published research on the role of differential resistance mechanisms of silver nanoparticles and silver ions in bacterial activity. Unlike the traditional antibacterial agent , the study of bacteria's resistance to silver nanoparticles (AgNPs) is still in its early stages, and its evolution mechanism is limited and uncertain. The core question remains whether bacterial resistance is driven by AgNPs, released Ag(I) ions, or a combination of these and other factors. Here, we demonstrated specific resistance of the Escherichia coli K-12 MG1655 strain to the sub-inhibitory concentration of AgNPs, rather than the Ag(I) ions, indicating that the minimum inhibitory concentration increased by more than twofold after 8 repeated passages after AgNPs were removed and reintroduced, which is statistically significant. Whole population genome sequencing found that a cusS mutation was associated with genetic resistance, possibly increasing silver ion efflux. Finally, we excluded the effects of particle aggregation antagonism and proposed that the mechanisms of resistance may be enhanced or mediated by flagellar-based motor.
Key points analysis
Key points 1: experimental design principles. E. coli multiple passages in a population repeatedly exposed to sub-inhibited concentrations of Ag(I) ions in response to AgNPs, as well as genetic stability of drug-resistant phenotypes transmitted when stress removal. The methods used included non-selected cell-only control populations and antibiotic sequence passage controls, and confirmed the drug resistance phenotype by robust statistical analysis. By comparing the drug resistance responses of highly motile E. coli K-12 MG1655 (+IS1) strains and non-motile E. coli K-12 JW1881 strains (ΔflhD::kan), the important role of bacterial motility (the key fitness trait of many bacteria) and other possible strain-specific traits in E. coli AgNP resistance is emphasized.
Picture and text introduction
Figure 1: high exercise (+IS1) E. coli drug resistance spectrum . a - c, resistance spectrum (purple triangle, c) for AgNPs (black triangle, a), Ag(I) ions (blue triangle, b) and ampicillin (positive control) were plotted as a doubling of MIC with passage algebra. Non-selective passage control under each condition is included in the red circle, which is associated with continuous passages of untreated bacteria, in which (i.e., the first time) one is exposed to the antibiotic of interest. The tan box indicates no antibacterial pressure.
Figure 2: Drug resistance spectrum of non-motile E. coli (ΔflhD::kan). a, b, resistance spectrum for AgNPs (black triangle, a) and ampicillin (positive control) (purple triangle, b), plotted as a multiplication of MIC with passage algebra. Channel control is included in the red circle. mean ±s.d. = 2-3 replicates. The non-motile E. coli (ΔflhD::kan) strain did not develop resistance to AgNPs and ampicillin .
Figure 3: AgNPs (12.5 μg ml−1) [AgNP]) were incubated in broth for 21 h and filtered with a 0.45 μm PVDF membrane filter to remove bacterial cells from aggregation before and after. a, c, after incubation with E. coli, the increase in particle size (hydrodynamic diameter) is shown by DLS. b, d, UV-visible-near-infrared absorption spectra (a.u) of any unit AgNPs show that after incubation with E. coli, the characteristic LSPr widens at λmax≈420 nm, indicating that aggregation is occurring. a, b, AgNPs of non-motile E. coli (agnp-sensitive only). c,d, AgNPs both exhibited similar aggregation behavior in the presence of highly active E. coli AgNP-sensitive strain and AgNP resistant strains (after passage 20).
Conclusion
This work study shows that after repeated exposure to sub-inhibitory concentrations of Ag(I) ions and AgNPs, the drug resistance response of highly motile and non-motile E. coli strains is different.AgNP resistance was found in highly motile E. coli (i.e., MIC increased statistically significantly more than twofold) and remained stable without returning to AgNP sensitivity, while non-motile E. coli did not show resistance. Permanent mutations of cusS were found in highly motile E. coli strains, suggesting that the direct mechanism of generating resistance by increasing silver ion efflux may be co-mediated or enhanced by the motor phenotype. These findings provide key insights into the development of bacteria's resistance to AgNPs, highlighting the potential role of bacterial motility. It is a good result to determine that bacterial motility may play an independent role outside of particle aggregation, as it guides future research to uncover detailed mechanisms of drug resistance. Furthermore, this study has great hope to find findings for reducing the burden of pathogenic diseases and infections, as there are many non-motivation, clinically relevant drug-resistant strains that are potential targets for AgNP treatment. CDC lists Clostridium difficile , Pseudomonas aeruginosa , Staphylococcus aureus , and various Acinetobacter and Streptococcus as urgent and serious threats, all of which are immobile, or in the case of Pseudomonas aeruginosa, which may occur in advanced and chronic infections. Our data suggest that AgNPs may be effective and remain effective against non-motor strains, without resistance or potential delayed resistance.
Full text link: https://doi.org/10.1038/s41565-021-00929-w
References: L.M. Stabryla, K.A. Johnston, N.A. Diemler, V.S. Cooper, J.E. Millstone, S.J. Haig, L.M. Gilbertson, Role of bacterial motility in differential resistance mechanisms of silver nanoparticles and silver ions, Nat Nanotechnol 16(9) (2021) 996-1003.
DOI: 10.1038/s41565-021-00929-w
Submission Contact: [email protected]
