Antimicrobial, antibiofilm, and antivirulence properties of Eisenia bicyclis-extracts and Eisenia bicyclis-gold nanoparticles towards microbial pathogens.

Nanomaterials derived from seaweed have developed as an alternative option for fighting infections caused by biofilm-forming microbial pathogens. This research aimed to discover potential seaweed-derived nanomaterials with antimicrobial and antibiofilm action against bacterial and fungal pathogens. Among seven algal species, the extract from Eisenia bicyclis inhibited biofilms of Klebsiella pneumoniae, Staphylococcus aureus, and Listeria monocytogenes most effectively at sub-MIC levels. As a result, in the present study, E. bicyclis was chosen as a prospective seaweed for producing E. bicyclis-gold nanoparticles (EB-AuNPs). Furthermore, the mass spectra of E. bicyclis reveal the presence of a number of potentially beneficial chemicals. The polyhedral shape of the synthesized EB-AuNP with a size value of 154.74 ± 33.46 nm was extensively described. The lowest inhibitory concentration of EB-AuNPs against bacterial pathogens (e.g., L.monocytogenes, S. aureus, Pseudomonas aeruginosa, and K. pneumoniae) and fungal pathogens (Candida albicans) ranges from 512 to >2048 µg/mL. Sub-MIC of EB-AuNPs reduces biofilm formation in P. aeruginosa, K. pneumoniae, L. monocytogenes, and S. aureus by 57.22 %, 58.60 %, 33.80 %, and 91.13 %, respectively. EB-AuNPs eliminate the mature biofilm of K. pneumoniae at > MIC, MIC, and sub-MIC concentrations. Furthermore, EB-AuNPs at the sub-MIC level suppress key virulence factors generated by P. aeruginosa, including motility, protease activity, pyoverdine, and pyocyanin, whereas it also suppresses the production of staphyloxanthin virulence factor from S. aureus. The current research reveals that seaweed extracts and a biocompatible seaweed-AuNP have substantial antibacterial, antibiofilm, and antivirulence actions against bacterial and fungal pathogens.

Antibiofilm and antivirulence activities of laminarin-gold nanoparticles in standard and host-mimicking media.

The rapidly rising antimicrobial resistance (AMR) in pathogenic bacteria has become one of the most serious public health challenges, with a high death rate. Most pathogenic bacteria have been recognized as a source of AMR and a primary barrier to antimicrobial treatment failure due to the development of biofilms and the production of virulence factors. In this work, nanotechnology was employed as a substitute method to control the formation of biofilms and attenuate virulence features in Pseudomonas aeruginosa and Staphylococcus aureus. We synthesized biocompatible gold nanoparticles from marine-derived laminarin as potential biofilm and virulence treatments. Laminarin-gold nanoparticles (Lam-AuNPs) have been identified as spherical, 49.84 ± 7.32 nm in size and - 26.49 ± 1.29 mV zeta potential. The MIC value of Lam-AuNPs against several drug-resistant microbial pathogens varied from 2 to 1024 µg/mL in both standard and host-mimicking media. Sub-MIC values of Lam-AuNPs were reported to effectively reduce the production of P. aeruginosa and S. aureus biofilms in both standard and host-mimicking growth media. Furthermore, the sub-MIC of Lam-AuNPs strongly reduced hemolysis, pyocyanin, pyoverdine, protease, and several forms of flagellar and pili-mediated motility in P. aeruginosa. Lam-AuNPs also inhibited S. aureus hemolysis and the production of amyloid fibrils. The Lam-AuNPs strongly dispersed the preformed mature biofilm of these pathogens in a dose-dependent manner. The Lam-AuNPs would be considered an alternative antibiofilm and antivirulence agent to control P. aeruginosa and S. aureus infections. KEY POINTS: • Lam-AuNPs were biosynthesized to control biofilm and virulence. • Lam-AuNPs show effective biofilm inhibition in standard and host-mimicking media. • Lam-AuNPs suppress various virulence factors of P. aeruginosa and S. aureus.

Description of Brachybacterium sillae sp. nov., a thermophilic bacterium isolated from a hot spring.

The taxonomic position of strain EF45031T, isolated from the Neungam Carbonate hot spring, was examined using the polyphasic taxonomic approach. Strain EF45031T shared the highest percentage of 16S rRNA gene sequence with Brachybacterium nesterenkovii CIP 104813 T (97.7%). The average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH) values between strain EF45031T and the type strains B. nesterenkovii CIP 104813 T and B. phenoliresistens Phenol-AT were 77.0%, 69.15%, 21.9% and 75.73%, 68.81%, 20.5%, respectively. Phylogenomic analysis using an up-to-date bacterial core gene (UBCG) set revealed that strain EF45031T belonged to the genus Brachybacterium. Growth occurred between 25 and 50 ℃ at pH 6.0-9.0 and could tolerate salinity up to 5% (w/v). Strain had anteiso-C15:0 and anteiso-C17:0 as major fatty acids. Menaquinone-7 (MK-7) was the predominant respiratory menaquinone. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, three aminolipids, and two unidentified glycolipids. The cell-wall peptidoglycan contained meso-diaminopimelic acid as a diagnostic diamino acid. The genome comprised 2,663,796 bp, with a G + C content of 70.9%. Stress-responsive periplasmic chaperone/protease coding genes were identified in the genome of EF45031T and were not detected in other Brachybacterium species. The polyphasic taxonomic properties indicate that the strain represents a novel species within the genus Brachybacterium, for which the name Brachybacterium sillae sp. nov. is proposed. The type strain is EF45031T (= KCTC 49702 T = NBRC 115869 T).

Description of Microbacterium neungamense sp. nov. isolated from a hot spring.

The Gram-positive, nonmotile, rod-shaped bacterium EF45044T was isolated from a hot spring in Chungju, South Korea. The strain was able to grow at concentrations of 0‒5% (w/v) NaCl, at pH 6.0‒10.0 and in the temperature range of 18‒50 °C. Strain EF45044T showed the highest 16S rRNA gene sequence similarity (98.2%) with Microbacterium ketosireducens DSM 12510T, and the digital DNA‒DNA hybridization (dDDH), average amino acid identity (AAI), and average nucleotide identity (ANI) values were all lower than the accepted species threshold. Strain EF45044T contained MK‒12 and MK‒13 as the predominant respiratory quinones and anteiso‒C17:0, anteiso‒C15:0, and iso‒C16:0 as the major fatty acids. Diphosphatidylglycerol, phosphatidylglycerol, and glycolipid were detected as the major polar lipids. The cell-wall peptidoglycan contained ornithine. The DNA G + C content was 71.4 mol%. Based on the polyphasic data, strain EF45044T (= KCTC 49703T) presents a novel species of the genus Microbacterium, for which the name Microbacterium neungamense sp. nov. is proposed.

Caffeine-loaded gold nanoparticles: antibiofilm and anti-persister activities against pathogenic bacteria.

The formation of biofilms by bacterial pathogens and the presence of persister cells in biofilms have become major concerns in the health sector, owing to their antibiotic resistance and tolerance. The transformation of bacterial pathogens into persister cells, either stochastically or due to stressful environmental factors, results in recalcitrant and recurring infections. Here, we sought to prepare gold nanoparticles from naturally occurring caffeine and explore their inhibitory action against biofilm formation and persister cells. Fourier transform infrared spectroscopy, UV-visible absorption spectroscopy, field emission transmission electron microscopy, energy-dispersive X-ray diffraction, and dynamic light scattering were used to characterize the gold nanoparticles obtained from caffeine (Caff-AuNPs). The Caff-AuNPs were found to exhibit a number of properties, including the ability to prevent biofilm formation, disperse mature biofilms, and kill different types of persister of gram-positive (Staphylococcus aureus and Listeria monocytogenes) and gram-negative (Pseudomonas aeruginosa and Escherichia coli) pathogenic bacteria. Microscopic analysis of the aforementioned bacterial cells, treated with Caff-AuNPs, revealed the bactericidal effect of Caff-AuNPs, although the underlying mechanism remains unknown. Collectively, the Caff-AuNPs synthesized in this study may be used as potential drugs to combat chronic infections caused by biofilm-forming pathogenic bacteria. KEY POINTS: • Biofilm and persister cells are clinically relevant, as they either prolong or completely resist antibiotic treatments. • Caffeine is used in the green synthesis of Caff-AuNPs, which have antibacterial and antibiofilm properties. • Caff-AuNPs are effective against various pathogenic bacterial persister cells.

Antibiofilm and Antivirulence Activities of Gold and Zinc Oxide Nanoparticles Synthesized from Kimchi-Isolated Leuconostoc sp. Strain C2.

The rapid emergence of antimicrobial resistance (AMR) among bacterial pathogens results in antimicrobial treatment failure and the high mortality rate associated with AMR. The application of nanoparticles synthesized from probiotics will be widely accepted due to their efficacy and biocompatibility in treating microbial infections in humans. The current work sought to isolate and identify lactic acid bacteria (LAB) from Kimchi. Based on 16S rRNA gene sequencing, the LAB isolate C2 was identified as a member of the genus Leuconostoc. The obtained supernatant from Leuconostoc sp. strain C2 was employed for the green synthesis of metal (AuNPs) and metal oxide (ZnONPs) nanoparticles. UV-vis absorption spectra, FTIR analysis, XRD, DLS, FE-TEM, and EDS mapping were used to fully characterize these C2-AuNPs and C2-ZnONPs. The C2-AuNPs were found to be spherical in shape, with a size of 47.77 ± 5.7 nm and zeta potential of -19.35 ± 0.67 mV. The C2-ZnONPs were observed to be rod-shaped and 173.77 ± 14.53 nm in size. The C2-ZnONPs zeta potential was determined to be 26.62 ± 0.35 mV. The C2-AuNPs and C2-ZnONPs were shown to have antimicrobial activity against different pathogens. Furthermore, these nanoparticles inhibited the growth of Candida albicans. The antibiofilm and antivirulence properties of these NPs against Pseudomonas aeruginosa and Staphylococcus aureus were thoroughly investigated. C2-AuNPs were reported to be antibiofilm and antivirulence against P. aeruginosa, whereas C2-ZnONPs were antibiofilm and antivirulence against both P. aeruginosa and S. aureus. Furthermore, these nanoparticles disrupted the preformed mature biofilm of P. aeruginosa and S. aureus. The inhibitory impact was discovered to be concentration-dependent. The current research demonstrated that C2-AuNPs and C2-ZnONPs exhibited potential inhibitory effects on the biofilm and virulence features of bacterial pathogens. Further studies are needed to unravel the molecular mechanism behind biofilm inhibition and virulence attenuation.

Inhibitory activities of phloroglucinol-chitosan nanoparticles on mono- and dual-species biofilms of Candida albicans and bacteria.

Phloroglucinol (PG) was encapsulated into chitosan nanoparticles (CSNPs) using a simple ionic gelification technique, and the inhibitory activity of the resulting nanoparticles on microbial mono- and dual-species biofilms was investigated. PG-CSNPs were determined to be spherical with a rough surface, and had an average diameter and zeta potential of 414.0 ± 48.5 nm and 21.1 ± 1.2 mV, respectively. The rate of PG release from the loaded CSNPs was found to increase in acidic environment. The loading capacity and encapsulation efficiency of PG to CSNPs were determined to be 18.74% and 22.4%, respectively. The prepared PG-CSNPs exhibited inhibitory effects on mono-species biofilms such as Candida albicans, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus mutans, and dual-species such as C. albicans-K. pneumoniae/S. aureus/S. mutans. The PG-CSNPs were found to be more effective in inhibiting and eradicating mono- and dual-species biofilms than pure PG. In addition, PG-CSNPs were found to enhance the efficacy of several antimicrobial drugs against mature mono- and dual-species biofilms. This work demonstrates that PG-CSNPs may provide an alternative method for treating infections caused by biofilm-forming pathogens.

Isolation and Characterization of Thermophilic Bacteria from Hot Springs in Republic of Korea.

Thermophiles that produce extracellular hydrolases are of great importance due to their applications in various industries. Thermophilic enzymes are of interest for industrial applications due to their compatibility with industrial processes, and the availability of the organisms is essential to develop their full potential. In this study, a culture-dependent approach was used to identify thermophilic bacteria from five hot springs in Republic of Korea. Characterization, taxonomic identification, and extracellular hydrolase (amylase, lipase, and protease) activity of 29 thermophilic bacterial isolates from the Neungam carbonate, Mungang sulfur, Deokgu, Baegam, and Dongnae hot springs were investigated. Identification based on the full-length 16S rRNA gene sequence revealed that strains belonged to the phylum Bacillota and were classified as Aeribacillus, Bacillus, Caldibacillus, Geobacillus, and Thermoactinomyces genera. It was found that 22 isolates could produce at least one extracellular enzyme. Geobacillus, representing 41.4% of the isolates, was the most abundant. The highest amount of proteolytic and lipolytic enzymes was secreted by strains of the genus Geobacillus, whereas Caldibacillus species produced the highest amount of amylolytic enzyme. The Geobacillus species producing hydrolytic extracellular enzymes appeared to be the most promising.

Draft genome sequence of the extremely halophilic Halorubrum sp. SAH-A6 isolated from rock salts of the Danakil depression, Ethiopia.

The draft genome sequence of Halorubrum sp. SAH-A6, isolated from commercial rock salts of the Danakil depression, Ethiopia. The genome comprised 3,325,770 bp, with the G + C content of 68.0%. The strain has many genes which are responsible for secondary metabolites biosynthesis, transport and catabolism as compared to other Halorubrum archaea members. Abundant genes responsible for numerous transport systems, solute accumulation, and aromatic/sulfur decomposition were detected. The first genomic analysis encourages further research on comparative genomics, and biotechnological applications. The NCBI accession number for this genome is SAMN04278861 and ID: 4278861 and strain deposited with accession number KCTC 43215.