Biology subjects

Kahru, A.

Publications and source records attributed to Kahru, A..

3 recordsLinked to original sources

bioRxiv2024

Do silver-chitosan nanocomposites promote bacterial resistance to silver or common antibiotics?

Silver-containing nanomaterials are versatile antimicrobials for slowing down the rapid increase of nosocomial infections caused by antibiotic-resistant bacteria. However, silver can also promote resistance in bacteria to both silver itself and conventional antibiotics. Despite this, the topic is still poorly studied. Silver-chitosan nanocomposites (nAgCSs) with a primary size of [~]50 nm and weight ratios of 1:1 (nAgCS-1) and 1:3 (nAgCS-3) were synthesised and studied for potential antimicrobials, such as wound dressings, antimicrobial coatings. These nAgCSs exhibited antibacterial efficacy at level of 6.25-14.6 mg Ag/L level (minimal inhibitory concentration, MIC) against Escherichia coli and Staphylococcus aureus being comparable to the efficiency of AgNO3 (MIC 3.13-7.29 mg Ag/L) or benzalkonium chloride (MIC 0.91-6.25 mg/L). Low molecular weight chitosan also demonstrated antibacterial activity against S. aureus (MIC 25 mg/L), though it was less effective against E. coli (MIC 70 mg/L). Notably, nAgCS-3 was almost as efficient as AgNO3 against S. aureus (MIC 6.25-7.29 mg/L) and benzalkonium chloride against E. coli (MIC 6. mg/L). Confocal laser scanning microscopy revealed a noticeable aggregation of S. aureus cells caused by exposure to nAgCS-3, an effect that was less pronounced in E. coli. The development of bacterial resistance to nAgCSs and AgNO3 and cross-resistance to 14 conventional antibiotics upon continuous exposure (up to 5 weeks) to sub-inhibitory concentrations (EC20) of the studied silver compounds was examined. No resistance development was observed for the studied silver compounds and antibiotics in either E. coli or S. aureus. Thus, silver-chitosan nanocomposites show promise as efficient and not AMR-inducing compounds for antimicrobial applications, such as wound dressings and surfaces.

microbiology↗

bioRxiv2020

Selective antibiofilm properties and biocompatibility of nano-ZnO and nano-ZnO/Ag coated surfaces

Spread of pathogenic microbes and antibiotic-resistant bacteria in health-care settings and public spaces is a serious public health challenge. Materials that prevent solid surface colonization or impede touch-transfer of viable microbes could provide means to decrease pathogen transfer from high-touch surfaces in critical applications. ZnO and Ag nanoparticles have shown great potential in antimicrobial applications. Less is known about nano-enabled surfaces. Here we demonstrate that surfaces coated with nano-ZnO or nano-ZnO/Ag composites are not cytotoxic to human keratinocytes and possess species-selective medium-dependent antibiofilm activity against Escherichia coli, Staphylococcus aureus and Candida albicans. Colonization of nano-ZnO and nano-ZnO/Ag surfaces by E. coli and S. aureus was decreased in static oligotrophic conditions (no planktonic growth). Moderate to no effect was observed for bacterial biofilms in growth medium (supporting exponential growth). Inversely, nano-ZnO surfaces enhanced biofilm formation by C. albicans in oligotrophic conditions. However, enhanced C. albicans biofilm formation on nano-ZnO surfaces was effectively counteracted by the addition of Ag. Possible selective enhancement of biofilm formation by the yeast C. albicans on Zn-enabled surfaces should be taken into account in antimicrobial surface development. Our results also indicated the importance of the use of application-appropriate test conditions and exposure medium in antimicrobial surface testing.

microbiology↗

bioRxiv2018

Bacterial plasma membrane is the main cellular target of silver nanoparticles in Escherichia coli and Pseudomonas aeruginosa

Silver nanoparticles (AgNP) are widely used in consumer products, mostly due to their excellent antimicrobial properties. One of the well-established antibacterial mechanisms of AgNP is their efficient contact with bacteria and dissolution on cell membranes. To our knowledge, the primary mechanism of cell wall damage and the event(s) initiating bactericidal action of AgNP are not yet elucidated.\n\nIn this study we used a combination of different assays to reveal the effect of AgNP on i) bacterial envelope in general, ii) outer membrane (OM) and iii) on plasma membrane (PM). We showed that bacterial PM was the main target of AgNP in Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. AgNP depolarized bacterial PM, induced the leakage of the intracellular K+, inhibited respiration and caused the depletion of the intracellular ATP. In contrast, AgNP had no significant effect on the bacterial OM. Most of the adverse effects on bacterial envelope and PM occurred within the seconds and in the concentration range of 7-160 M AgNP, depending on the bacteria and assay used, while irreversible inhibition of bacterial growth (minimal bactericidal concentration after 1-h exposure of bacteria to AgNP) occurred at 40 M AgNP for P. aeruginosa and at 320 M AgNP for E. coli.\n\nFlow cytometry analysis showed that AgNP were binding to P. aeruginosa but not to E. coli cells and were found inside the P. aeruginosa cells. Taking into account that AgNP did not damage OM, we speculate that AgNP entered P. aeruginosa via specific mechanism, e.g., transport through porins.

microbiology↗