Biocompatibility and biocidal effects of modified polylactide composites.

Polylactide (PLA) materials treated with antimicrobial fillers represent a suitable alternative to the production of medical devices. Their advantage is that they can prevent the growth of microorganisms and the formation of microbial biofilms on the surface and around composites. The work is focused on the evaluation of biocompatibility and biocide effect of PLA composite films filled with vermiculite and graphene oxide modified with silver (Ag+ and Ag nanoparticles), hexadecylpyridinium (HDP) and hexadecyltrimethylammonium (HDTMA) cations and their degradation leachates monitored at 1-3-6-month intervals. The antimicrobial effect of the leachates was detected by microdilution methods on gram-negative (Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis), gram-positive (Staphylococcus aureus, Streptococcus salivarius) bacteria and yeast (Candida albicans). The biocidal effect of composites on biofilm formation on the surface of composites was monitored by Christensen method and autoaggregation and motility tests. The biocompatibility of the composite and the leachates was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) cytotoxicity assay. The evaluation of the antimicrobial effect of the leachates demonstrated that leachates of PLA composite filled with graphene oxide and Ag+ showed a stronger antimicrobial effect than leachates of PLA composite filled with vermiculite and Ag+ and Ag nanoparticles. The leachates of PLA composites containing vermiculite with HDP and HDTMA cations had a higher antimicrobial effect on G+ bacteria and yeast than G- bacteria. Bacterial growth, biofilm formation, autoaggregation and motility of the tested bacteria were most inhibited by the composite with vermiculite and Ag+ and Ag nanoparticles. Even after a 6-month degradation of this composite, bacterial growth and biofilm formation continued to be strongly inhibited up to 42 and 91%, respectively. The cytotoxic effect was proved only in the leachate of the composite with vermiculite containing HDP after 6 months of its degradation. Tests evaluating the biocompatibility of materials have shown that the vermiculite is the most preferred carrier and can be used in the future to bind other compounds. The study confirmed that PLA composite filled with vermiculite and Ag+ and Ag nanoparticles was the most stable and effective composite with the best biocompatible and biocidal properties.

Resistant Genes and Multidrug-Resistant Bacteria in Wastewater: A Study of Their Transfer to the Water Reservoir in the Czech Republic.

Wastewater is considered the most serious source of the spread of antibiotic resistance in the environment. This work, therefore, focuses on the fate and spread of antibiotic resistance genes (ARGs) in wastewater and the monitoring of multidrug-resistant strains. ARGs were monitored in the nitrification and sedimentation tanks of the wastewater treatment plant (WWTP) and in the dam into which this WWTP flows, at various times. The highest relative abundance was found for the blaTEM > tetW > blaNDM-1 > vanA resistance genes, respectively. An increased concentration of tetracycline (up to 96.00 ng/L) and ampicillin (up to 19.00 ng/L) was found in water samples compared to other antibiotics detected. The increased incidence of seven ARGs and four antibiotics was observed in the November and December sampling times. Isolated ampicillin-resistant strains showed a high degree of resistance to ampicillin (61.2% of the total isolates had a minimum inhibitory concentration (MIC) ≥ 20 mg/mL). In 87.8% of isolates, out of the total number, the occurrence of two or more ARGs was confirmed. These multidrug-resistant strains were most often identified as Aeromonas sp. This strain could represent a significant role in the spread of multidrug resistance through wastewater in the environment.

Beta-lactam resistance development during the treatment processes of municipal wastewater treatment plants.

This work monitored the effect of a municipal and a village wastewater treatment plant (WWTP) technology on the fate of beta-lactam resistance genes in bacterial populations in different phases of the wastewater treatment process. In case of the municipal WWTP1, the bacteria possessing a high ampicillin resistance (minimal inhibitory concentration (MIC) values of 20 mg/mL) accumulated in the sedimentation tank, which was accompanied with a higher concentration of ampicillin in the wastewater samples (28.09 ng/L) and an increase in the relative abundance of the blaTEM gene in the bacterial population. However, an opposite trend was revealed with the blaNDM-1 gene, making the sedimentation processes of WWTP1 crucial only for the accumulation of the blaTEM gene. Similarly, the comparison with the WWTP2 showed that the accumulation of the ampicillin resistance in bacterial population probably depended on the WWTP technology and wastewater composition. Out of the four tested resistance genes (blaTEM, blaKPC, blaNDM-1, and blaOXA-48), blaTEM and blaNDM-1 genes were the only two detected in this study. According to NGS analysis of bacterial 16 S rRNA gene, Gammaproteobacteria dominated the ampicillin-resistant bacteria of the WWTP sedimentation tanks. Their relative abundance in the bacterial population also increased during the sedimentation processes in WWTP1. It could indicate the role of the bacterial taxon in ampicillin resistance accumulation in this WWTP and show that only 9.29% of the original bacterial population from the nitrification tank is involved in the documented shifts in beta-lactam resistance of the bacterial population.

In-Depth Bioinformatic Analyses of Nidovirales Including Human SARS-CoV-2, SARS-CoV, MERS-CoV Viruses Suggest Important Roles of Non-canonical Nucleic Acid Structures in Their Lifecycles.

Non-canonical nucleic acid structures play important roles in the regulation of molecular processes. Considering the importance of the ongoing coronavirus crisis, we decided to evaluate genomes of all coronaviruses sequenced to date (stated more broadly, the order Nidovirales) to determine if they contain non-canonical nucleic acid structures. We discovered much evidence of putative G-quadruplex sites and even much more of inverted repeats (IRs) loci, which in fact are ubiquitous along the whole genomic sequence and indicate a possible mechanism for genomic RNA packaging. The most notable enrichment of IRs was found inside 5'UTR for IRs of size 12+ nucleotides, and the most notable enrichment of putative quadruplex sites (PQSs) was located before 3'UTR, inside 5'UTR, and before mRNA. This indicates crucial regulatory roles for both IRs and PQSs. Moreover, we found multiple G-quadruplex binding motifs in human proteins having potential for binding of SARS-CoV-2 RNA. Non-canonical nucleic acids structures in Nidovirales and in novel SARS-CoV-2 are therefore promising druggable structures that can be targeted and utilized in the future.

Antimicrobial Synergistic Effect Between Ag and Zn in Ag-ZnO·mSiO2 Silicate Composite with High Specific Surface Area.

Antimicrobial materials are widely used for inhibition of microorganisms in the environment. It has been established that bacterial growth can be restrained by silver nanoparticles. Combining these with other antimicrobial agents, such as ZnO, may increase the antimicrobial activity and the use of carrier substrate makes the material easier to handle. In the paper, we present an antimicrobial nanocomposite based on silver nanoparticles nucleated in general silicate nanostructure ZnO·mSiO2. First, we prepared the silicate fine net nanostructure ZnO·mSiO2 with zinc content up to 30 wt% by precipitation of sodium water glass in zinc acetate solution. Silver nanoparticles were then formed within the material by photoreduction of AgNO3 on photoactive ZnO. This resulted into an Ag-ZnO·mSiO2 composite with silica gel-like morphology and the specific surface area of 250 m2/g. The composite, alongside with pure AgNO3 and clear ZnO·mSiO2, were successfully tested for antimicrobial activity on both gram-positive and gram-negative bacterial strains and yeast Candida albicans. With respect to the silver content, the minimal inhibition concentration of Ag-ZnO·mSiO2 was worse than AgNO3 only for gram-negative strains. Moreover, we found a positive synergistic antimicrobial effect between Ag and Zn agents. These properties create an efficient and easily applicable antimicrobial material in the form of powder.