Sensitive Detection of Staphylococcus aureus with Vancomycin-Conjugated Magnetic Beads as Enrichment Carriers Combined with Flow Cytometry

The potential risks of paclobutrazol residue on yogurt fermentation from the level of chiral enantiomers

In recent years, pesticide residues in food have increasingly become the focus of public attention. However, the standard system of pesticide maximum residue limits in fermented food is imperfect, which can lead to potential safety risks to consumers. In this context, the aim of the study was to assess the potential effects of paclobutrazol residue on the yogurt fermentation process. We examined the stereoselective behaviors of the 2 paclobutrazol enantiomers from the perspective of chirality during the yogurt fermentation process. The results indicated that no significant degradation occurred for either of the 2 enantiomers (2R, 3R-paclobutrazol, 2S, 3S-paclobutrazol), and no visible enantiomer conversion behavior was observed. In addition, the reason paclobutrazol did not significantly degrade was explained from the perspective of the microbial function. Results from 16S rRNA sequencing indicated that paclobutrazol significantly affected the microbial composition and inhibited metabolic function of microorganisms to exogenous substances, which impeded the degradation of residual pesticide in yogurt. Furthermore, the stable residue of exogenous substance may cause potential food safety problems. Microbial α-diversity analysis indicated that fermentation time played a more important role on diversity than did paclobutrazol concentration. Moreover, Staphylococcus was found in yogurt after treatment with paclobutrazol; Staphylococcus aureus causes dangerous infectious diseases in humans. We devised a method to investigate the presence of pesticide residues during food fermentation and provided a theoretical basis for food safety assessment.

A novel flow cytometry assay based on bacteriophage-derived proteins for Staphylococcus detection in blood

Bloodstream infections (BSIs) are considered a major cause of death worldwide. Staphylococcus spp. are one of the most BSIs prevalent bacteria, classified as high priority due to the increasing multidrug resistant strains. Thus, a fast, specific and sensitive method for detection of these pathogens is of extreme importance. In this study, we have designed a novel assay for detection of Staphylococcus in blood culture samples, which combines the advantages of a phage endolysin cell wall binding domain (CBD) as a specific probe with the accuracy and high-throughput of flow cytometry techniques. In order to select the biorecognition molecule, three different truncations of the C-terminus of Staphylococcus phage endolysin E-LM12, namely the amidase (AMI), SH3 and amidase+SH3 (AMI_SH3) were cloned fused with a green fluorescent protein. From these, a higher binding efficiency to Staphylococcus cells was observed for AMI_SH3, indicating that the amidase domain possibly contributes to a more efficient binding of the SH3 domain. The novel phage endolysin-based flow cytometry assay provided highly reliable and specific detection of 1-5 CFU of Staphylococcus in 10 mL of spiked blood, after 16 hours of enrichment culture. Overall, the method developed herein presents advantages over the standard BSIs diagnostic methods, potentially contributing to an early and effective treatment of BSIs.

Bacterial Detection and Elimination Using a Dual-Functional Porphyrin-Based Porous Organic Polymer with Peroxidase-Like and High Near-Infrared-Light-Enhanced Antibacterial Activity

The efficient fabrication of multifunctional nanoplatforms for bacterial detection and elimination is of great importance in nanobiotechnology. A new porphyrin-based porous organic polymer, FePPOP_BFPB, was synthesized via the reaction between pyrrole and 4-{2,2-bis[(4-formylphenoxy)methyl]-3-(4-formylphenoxy) propoxy} benzaldehyde (BFPB). The C-centric tetrahedral structure of BFPB promoted the formation of FePPOP_BFPB with a 3D interconnected porous structure, high specific surface area, and plentiful surface catalytic active sites. The adjustable structural alkyl chain also enhanced the absorption capability of FePPOP_BFPB in the long-wavelength visible and near-infrared regions (NIR). FePPOP_BFPB exhibited excellent peroxidase-like activity toward a representative peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂. Utilizing these features, a rapid and visual detection of Staphylococcus aureus (S. aureus) based on FePPOP_BFPB was established and exhibited high sensitivity and stability. Combining the catalysis with near-infrared-light (NIR) absorption, FePPOP_BFPB can effectively catalyze the decomposition of biologically relevant concentrations of H₂O₂ to produce vast amounts of •OH radicals via the photo-Fenton reaction, which avoids the utilization of high toxic concentrations of H₂O₂. On the basis of these satisfactory features, FePPOP_BFPB had a conspicuous bactericidal performance against S. aureus under NIR irradiation. To our knowledge, this is the first example of a porphyrin-based porous organic polymer antibacterial agent. The main reactive oxygen species (ROS) produced in this system and the possible antibacterial mechanism of FePPOP_BFPB was also proposed through a series of experiments.

Streptavidin-exposed magnetic nanoparticles for lectin magnetic separation (LMS) of Staphylococcus aureus prior to three quantification strategies

A lectin magnetic separation (LMS) method for Staphylococcus aureus (S. aureus) was developed with the aim to improve the efficiency of magnetic nanoparticles and to expand the scope of bacterial recognition. Poly(ethylene glycol) (PEG)-mediated magnetic nanoparticles modified with streptavidin (MNP-PEG-SA) were synthesized and then applied to a two-step LMS based on the use of wheat germ agglutinin (WGA). Three specific methods for S. aureus detection (suitable for different requirements including detection time and sensitivity) were designed. The new LMS has improved anchoring efficiency (compared to two-step LMS methods) and requires a reduced number of magnetic particles. The Baird-Parker (B-P) method can detect S. aureus with a detection limit of 3 × 10⁰ CFU·mL^-1 within 15 h; the polymerase chain reaction (PCR) method can be finished within 4 h, with the lowest detection limit (LOD) of 3 × 10² CFU·mL^-1. The LOD of HRP-pig IgG-based colorimetric method is 3 × 10⁵ CFU·mL^-1, and the method only lasts for 2 h. If combined with specific detection methods, it meets different needs for rapid detection of S. aureus. Graphical abstractSchematic representation of lectin magnetic separation (LMS) based on biotin-wheat germ agglutinin (WGA) and poly (ethylene glycol) (PEG)-mediated streptavidin-modified magnetic nanoparticles (MNP-PEG-SA) and three different quantification strategies (including B-P culture assay, PCR assay, and colorimetric assay) for S. aureus.

Daptomycin-modified magnetic beads integrated with lysostaphin for selective analysis of Staphylococcus

An antibiotic-affinity method was developed for analyzing Staphylococcus on the basis of the strong binding capability of daptomycin towards Gram-positive bacteria cellular membrane, as well as the selective lytic action of lysostaphin towards Staphylococcus. Daptomycin-modified magnetic beads were adopted to enrich Staphylococcus from sample matrix. Afterwards lysostaphin was adopted to lyse Staphylococcus, which can hydrolyze pentaglycine cross-linkers of peptidoglycan composing the cellular wall of Staphylococcus. The concentration of Staphylococcus was quantified by collecting the bioluminescent signal of the released intracellular adenosine triphosphate of the enriched Staphylococcus. Staphylococcus aureus (S. aureus) was analyzed as a model bacterium to study the feasibility of the proof-of-principle work. For bioluminescent analysis of S. aureus with the developed method, the linear range was 5.0 × 10²-5.0 × 10⁶ colony forming units mL^-1, and the limit of detection was 3.8 × 10² colony forming units mL^-1. The analytical procedure consisting of bacterial enrichment, cell lysis and signal collection can be accomplished within 20 min. Some common Gram-positive bacteria and Gram-negative bacteria all indicated very low interference to the analysis of the target bacterium. It has been successfully used to analyze S. aureus in milk as well as physiological saline injection, indicating its application potential for real samples.

Lysin cell-binding domain-functionalized magnetic beads for detection of Staphylococcus aureus via inhibition of fluorescence of Amplex Red/hydrogen peroxide assay by intracellular catalase

Accurate and rapid identification of Staphylococcus aureus (S. aureus) is of great significance for controlling the food poisoning and infectious diseases caused by S. aureus. In this study, a novel strategy that combines lysin cell-binding domain (CBD)-based magnetic separation with fluorescence detection was developed for the specific and sensitive quantification of S. aureus in authentic samples. The S. aureus cells were separated from the sample matrix by lysin CBD-functionalized magnetic beads. Following lysis by lysostaphin, intracellular catalase was released from S. aureus cells and detected by a fluorometric system composed of horseradish peroxidase (HRP), hydrogen peroxide (H₂O₂), and Amplex Red. S. aureus was quantified via the inhibitory effect of the released intracellular catalase on the fluorometric system since the catalase could decompose the H₂O₂. Optimized conditions afforded a calibration curve for S. aureus ranging from 1.0 × 10² to 1.0 × 10⁷ CFU mL^-1. The detection limit was as low as 78 CFU mL^-1 in phosphate-buffered saline (PBS), and the total detection process could be completed in less than 50 min. Other bacteria associated with common food-borne and nosocomial infections negligibly interfered with S. aureus detection, except for Staphylococcus epidermidis, which may have slightly interfered. Moreover, the potential of this proposed method for practical applications has been demonstrated by detection assays of sterilized milk and human serum. Graphical abstract.

Antibiotic-affinity chromatographic test strip for quantitative analysis and antibiotic resistance testing of Staphylococcus aureus

Bacterial analysis and antibiotic resistance testing (ART) are of great significance in clinical diagnosis and therapy of bacterial infectious diseases. In this work, a portable antibiotic-affinity chromatographic test strip has been developed for rapid analysis of Staphylococcus aureus (S. aureus) and further applied for ART of this pathogen. Porcine IgG was immobilized on a nitrocellulose membrane for capturing S. aureus based on the selective binding capability of the Fc fragment of IgG toward protein A on the surface of the target bacteria. Fluorescent microspheres modified with teicoplanin (TEI) were applied as signal substances to trace S. aureus utilizing the hydrogen bond conjugation between this antibiotic and Gram-positive bacteria. S. aureus can be analyzed within the concentration range from 1.4 × 10³ CFU mL^-1 to 1.4 × 10⁷ CFU mL^-1. The recovery values for spiked samples were 93.3-110.0%. The obtained results of ART for penicillin, daptomycin, gentamicin, cefoxitin and clindamycin against S. aureus showed agreement with those of traditional broth dilution method. The procedures for bacterial analysis and ART can be accomplished within 20 and 110 min, respectively. The antibiotic-affinity chromatographic test strip showed great promise in point-of-care testing because of its ideal portability and rapidity.

Electrochemical immunosensor based on an antibody-hierarchical mesoporous SiO2 for the detection of Staphylococcus aureus

The outbreak of food-borne pathogens has become a serious concern; therefore, the detection of pathogenic bacteria in food is required. Untreated, sensitive, and reliable sensors should be developed for the detection of Staphylococcus aureus (S. aureus). In this study, a sensitive antibody-based electrochemical immunosensor was developed using antibody (Ab)-hierarchical mesoporous silica (HMS) bio-conjugates for label-free detection of low concentrations of S. aureus. First, a bio-template method based on butterfly wings was used to prepare the HMS. Then, the carrier material was amino-functionalized to cross-link the antibody with glutaraldehyde. The Ab-HMS bio-conjugates were then immobilized on a glassy carbon electrode (GCE), and the presence of S. aureus was detected by analyzing the changes in the peak currents after the antigen-antibody complex formation. Differential pulse voltammetry (DPV) was performed with bacterial concentrations ranging from 10 to 2 × 103 colony forming units (CFU) mL-1. Selective tests were performed using Escherichia coli (E. coli), Listeria monocytogenes (L. monocytohenes), and Salmonella, and the selective assays showed specific detection of S. aureus using the sensor. In addition, the immunosensor showed a good linear relationship between the peak current increase and logarithmic S. aureus concentration (R 2 = 0.9759) with a fast detection time (20 min) and detection limit of 11 CFU mL-1. When the electrochemical impedance spectroscopy (EIS) was performed under the same conditions, the results showed a good linear relationship between the impedance change value and the bacterial concentration (R 2 = 0.9720), the limit of detection (LOD) was 12 CFU mL-1. The performance of the sensor was compared with that of the colony counting method in the spiked milk sample test. The results showed no significant difference in the test results. Hence, this electrochemical immunosensor can be used to quickly detect S. aureus in actual food samples with a high sensitivity, specificity and stability.

Fluorescent analysis of Staphylococcus aureus by using daptomycin and immunoglobulin G for dual sites affinity

A dual sites affinity protocol was developed for fluorescent analysis of Staphylococcus aureus (S. aureus) by employing daptomycin and immunoglobulin G (IgG) as the recognition elements. Pig IgG immobilized on microplate was employed as the first recognition element to capture S. aureus owing to the fact that the Fc segment of mammal IgG can selectively bind with protein A on the surface of the target bacteria. Meanwhile, fluorescein isothiocyanate-conjugated daptomycin was employed as the second recognition element as well as the signal tracer for the target bacteria utilizing the binding capability of daptomycin to Gram-positive bacteria. S. aureus can be analyzed within a concentration range of 5.0 × 10³-5.0 × 10⁸ CFU mL^-1 with a detection limit of 3.6 × 10³ CFU mL^-1. The analytical process can be accomplished within 1.5 h by using a pre-coated microplate. The dual sites affinity protocol can exclude the interference led by Gram-negative bacteria and other common Gram-positive bacteria. We have successfully applied it to analyze S. aureus in spiked lake water and physiological saline injection samples, and the recovery values ranged from 88.0% to 120.0%. The results demonstrate its application potential for environmental sanitation and drug safety control.

Functional chimera aptamer and molecular beacon based fluorescent detection of Staphylococcus aureus with strand displacement-target recycling amplification

A fluorescent detection of Staphylococcus aureus (S. aureus) is established based on a finely designed functional chimera sequence, a molecular beacon (MB), and strand displacement target recycling. The chimera sequence, which consists of the aptamer sequence of S. aureus and the complementary sequence of MB, can form a hairpin structure due to the existence of intramolecular complementary regions. When S. aureus is present, it binds to the aptamer region of the chimera, opens the hairpin and unlocks the complementary sequence of MB. Subsequently, the MB is opened and intensive fluorescence signal is restored. To increase the sensitivity of the detection, signal amplification is achieved through strand displacement-based target recycling. With the catalysis of Nb. Bpu10I nicking endonuclease and Bsm DNA polymerase, the MB sequence can be cleaved and then elongated to form a complete duplex with the chimera, during which S. aureus is displaced from the chimera and proceeded to the next round of the reaction. This assay displays a linear correlation between the fluorescence intensity and the logarithm of the concentration of S. aureus within a broad concentration range from 80 CFU/mL to 8 × 10⁶ CFU/mL. The detection limit of 39 CFU/mL can be derived. The assay was applied to detect S. aureus in different water samples, and satisfactory recovery and repeatability were achieved. Hence the designed chimera sequence and established assay have potential application in environmental pollution monitoring.

Peptidoglycan binding protein (PGBP)-modified magnetic nanobeads for efficient magnetic capturing of Staphylococcus aureus associated with sepsis in blood

Peptidoglycan-binding protein-modified magnetic nanobeads (PGBP-MNBs) were prepared for efficient magnetic capturing of Staphylococcus aureus (S. aureus), which is associated with sepsis, using the binding affinity of PGBP for the peptidoglycan (PG) layer on S. aureus. These PGBP-MNBs can simply capture S. aureus in plasma within 1 hr or even 15 min. Importantly, they also can capture various types of Gram-positive bacteria, such as Bacillus cereus and methicillin-resistant and methicillin-susceptible S. aureus (MRSA and MSSA). We believe that PGBP-based systems will be used to develop diagnostic systems for Gram-positive bacteria-related diseases.

Atomic Force Microscopy Imaging Study of Aligning DNA by Dumbbell-like Au-Fe3O4 Magnetic Nanoparticles

Studies on nucleic acid structure and interactions between nucleic acid and its binding molecules are of great importance for understanding and controlling many important biological processes. Atomic force microscopy (AFM) imaging is one of the most efficient methods to disclose the DNA structure and binding modes between DNA and DNA-binding molecules. Long-chain DNA tends to form a random coiled structure, which prevents direct AFM imaging observation of the subtle structure formed by DNA itself or protein binding. Aligning DNA from the random coiled state into the extended state is not only important for applications in DNA nanotechnology but also for elucidating the interaction mechanism between DNA and other molecules. Here, we developed an efficient method based on the magnetic field to align long-chain DNA on a silicon surface. We used AFM imaging to study the alignment of DNA at the single-molecule level, showing that DNA can be stretched and highly aligned by the manipulation of magnetic nanoparticles tethered to one end of DNA and that the aligned DNA can be imaged clearly by AFM. In the absence of the magnetic field, the aligned DNA can relax back to a random coiled state upon rinsing. Such alignment and relaxation can be repeated many times, which provides an efficient method for the manipulation of individual DNA molecules and the investigation of DNA and DNA-binding molecule interactions.

Metal Nanoparticles for Diagnosis and Therapy of Bacterial Infection

Infectious diseases caused by pathogenic bacteria, especially multidrug-resistant bacteria, and their global spreading have become serious public health concerns. Early diagnosis and effective therapy can efficiently prevent deterioration and further spreading of the infections. There is an urgent need for sensitive, selective, and facile diagnosis as well as therapeutically potent treatment. The emergence of nanotechnology has provided more options for diagnosis and treatments of bacterial infections. Metal nanoparticles and metal oxide nanoparticles have drawn intense attention owing to their unique optical, magnetic, and electrical properties. These versatile metal-based nanoparticles have great potential for selective detection of bacteria and/or therapy. This review gives an overview of recent efforts on developing various metal-based nanoparticles for bacterial detection and infection therapy. It begins with an introduction of fundamental concepts and mechanisms in designing diagnostic and therapeutic strategies. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. A brief discussion of challenges and perspective outlook in this field is provided at the end of this review.