Rikenella microfusus is an essential intestinal probiotic with great potential. The latest research shows that imbalance in the intestinal flora are related to the occurrence of various diseases, such as intestinal diseases, immune diseases, and metabolic diseases. Rikenella may be a target or biomarker for some diseases, providing a new possibility for preventing and treating these diseases by monitoring and optimizing the abundance of Rikenella in the intestine. However, the current monitoring methods have disadvantages, such as long detection times, complicated operations, and high costs, which seriously limit the possibility of clinical application of microbiome-based treatment options. Therefore, the intention of this study was to evolve an enriched aptamer library to be used for specific labeling of R. microfusus, allowing rapid and low-cost detection methods and, ultimately the construction of aptamer-based biosensors. In this study, we used Rikenella as the target bacterium for an in vitro whole Cell-SELEX (Systematic Evolution of Ligands by EXponential Enrichment) to evolve and enrich specific DNA oligonucleotide aptamers. Five other prominent anaerobic gut bacteria were included in this process for counterselection and served as control cells. The aptamer library R.m-R13 was evolved with high specificity and strong affinity (K_d = 9.597 nM after 13 rounds of selection). With this enriched aptamer library, R. microfusus could efficiently be discriminated from the control bacteria in complex mixtures using different analysis techniques, including fluorescence microscopy or fluorometric suspension assays, and even in human stool samples. These preliminary results open new avenues toward the development of aptamer-based microbiome bio-sensing applications for fast and reliable monitoring of R. microfusus.

The diminishing portfolio of mankind’s available antibiotics urges science to develop novel potent drugs. Here, we present a peptide fitting the typical blueprint of amphipathic and membrane-active antimicrobial peptides, denominated C14R. This 2 kDa peptide consists of 16 amino acid residues, with seven being either hydrophobic, aromatic, or non-polar, and nine being polar or positively charged, strictly separated on opposite sides of the predicted α-helix. The affinity of the peptide C14R to P. aeruginosa membranes and its intrinsic tendency to productively insert into membranes of such composition were analyzed by dynamic simulations. Its biological impact on the viability of two different P. aeruginosa reference strains was demonstrated by determining the minimal inhibitory concentrations (MICs), which were found to be in the range of 10–15 µg/mL. C14R’s pore-forming capability was verified in a permeabilization assay based on the peptide-triggered uptake of fluorescent dyes into the bacterial cells. Finally, the peptide was used in radial diffusion assays, which are commonly used for susceptibility testing of antimicrobial peptides in clinical microbiology. In comparison to reference strains, six clinical P. aeruginosa isolates were clearly affected, thereby paving the way for further in-depth analyses of C14R as a promising new AMP drug in the future.

Rikenella microfusus is an essential intestinal probiotic with great potential. The latest research shows that its imbalance in the intestinal flora is related to the occurrence of various diseases, such as intestinal diseases, immune diseases, and metabolic diseases. Rikenella may be a target or biomarker for some diseases, providing a new possibility for preventing and treating these diseas-es by monitoring and changing the abundance of Rikenella in the intestine. However, the current detection methods have disadvantages such as long detection time, complicated operation, and high cost, which seriously limit the possibility of clinical application of this new treatment method. Therefore, developing rapid and low-cost detection methods has become an urgent problem to be solved. In this study, we used Rikenella as the target bacterium, meanwhile including five other prominent gut bacteria Akkermansia muciniphila, Allobaculum stercoricanis, Blautia producta, Rose-buria intestinalis and Parabacteroides distasonis as control organisms. The aptamer library R.m-R13 was evolved with high specificity and strong affinity (Kd = 9.597 nM) in an iterative Cell-SELEX process after 13 rounds of selection. R. microfusus can efficiently be discriminated from other major gut bacteria in complex mixtures in different analysis techniques including fluorescence micros-copy or fluorometric suspension assays and even in human stool samples. These preliminary re-sults open new avenues towards the development of aptamer-based microbiome bio-sensing ap-plications for fast and reliable R. microfusus monitoring.

Infections caused by yeasts of the genus Candida are likely to occur not only in immunocompromised patients but also in healthy individuals, leading to infections of the gastrointestinal tract, urinary tract, and respiratory tract. Due to the rapid increase in the frequency of reported Candidiasis cases in recent years, diagnostic research has become the subject of many studies, and therefore, we developed a polyclonal aptamer library-based fluorometric assay with high specificity and affinity towards Candida spec. to quantify the pathogens in clinical samples with high sensitivity. We recently obtained the specific aptamer library R10, which explicitly recognized Candida and evolved it by mimicking an early skin infection model caused by Candida using the FluCell-SELEX system. In the follow-up study presented here, we demonstrate that the aptamer library R10-based bioassay specifically recognizes invasive clinical Candida isolates, including not only C. albicans but also strains like C. tropcialis, C. krusei, or C. glabrata. The next-generation fluorometric bioassay presented here can reliably and easily detect an early Candida infection and could be used for further clinical research or could even be developed into a full in vitro diagnostic tool.

Background/Objectives: Infections caused by Candida albicans, Candidozyma auris, and Candida parapsilosis increasingly challenge current treatment options as resistance to currently used antifungals is continuously developing. Neutralizing antimicrobial peptides (nAMPs), which modulate pathogenic behavior rather than inducing cell death, represent a promising approach to fighting against fungal infections. Methods: This study established a whole-cell phage display workflow to identify novel nAMPs, and therefore three independent biopanning processes with the Ph.D.-12 phage display library against C. albicans, C. auris, and C. parapsilosis cells were conducted. Results: Phage display produced species-selective, high-affinity peptides that were non-cytotoxic to human cells and did not affect planktonic Candida viability. These peptides inhibited early biofilm formation, and several also slowed early biofilm maturation down. Conclusions: These findings demonstrate that whole-cell phage display as a powerful and adaptable discovery tool is suitable for identifying nAMPs that neutralize biofilm development without toxicity towards human cells. Beyond the peptides described here, this approach expands the methodological toolbox for antifungal research and provides a sustainable approach for generating targeted peptides.

The global rise in antimicrobial resistance among the ESKAPE pathogens represents a major challenge to public health. Here, we report the broad-spectrum antibacterial activity of the synthetic antimicrobial and pore-forming peptide C14R against all six ESKAPE species. Using a radial diffusion assay and resazurin-based viability testing, C14R exhibited a potent bactericidal effect with minimum inhibitory concentrations (MICs), defined as the lowest concentration of an antimicrobial agent that completely inhibits visible growth of planktonic microorganisms, ranging from 3.4 µg/mL (Enterococcus faecium, vancomycin-resistant) to 45.2 µg/mL (Klebsiella quasipneumoniae, ESBL). C14R also inhibited biofilm formation by Gram-positive pathogens, with minimum biofilm inhibitory concentrations (MBICs), referring to the minimal concentration required to prevent the development of biofilms, of 15.0 µg/mL (Staphylococcus aureus, MRSA) and 22.0 µg/mL (E. faecium, VRE), whereas Gram-negative biofilms showed higher tolerance. Together, these findings demonstrate that C14R retains high activity against multidrug-resistant ESKAPE strains, highlighting its potential as a lead compound for the development of next-generation antimicrobial drugs to expand the portfolio of available antibiotics and brace health systems against emerging severe infections.