Aggregation-Based Bacterial Separation with Gram-Positive Selectivity by Using a Benzoxaborole-Modified Dendrimer.

Antimicrobial-resistant (AMR) bacteria have become a critical global issue in recent years. The inefficacy of antimicrobial agents against AMR bacteria has led to increased difficulty in treating many infectious diseases. Analyses of the environmental distribution of bacteria are important for monitoring the AMR problem, and a rapid as well as viable pH- and temperature-independent bacterial separation method is required for collecting and concentrating bacteria from environmental samples. Thus, we aimed to develop a useful and selective bacterial separation method using a chemically synthesized nanoprobe. The metal-free benzoxaborole-based dendrimer probe BenzoB-PAMAM(+), which was synthesized from carboxy-benzoxaborole and a poly(amidoamine) (PAMAM) dendrimer, could help achieve Gram-positive bacterial separation by recognizing Gram-positive bacterial surfaces over a wide pH range, leading to the formation of large aggregations. The recognition site of benzoxaborole has a desirable high acidity and may therefore be responsible for the improved Gram-positive selectivity. The Gram-positive bacterial aggregation was then successfully collected by using a 10 µm membrane filter, with Gram-negative bacteria remaining in the filtrate solution. BenzoB-PAMAM(+) will thus be useful for application in biological analyses and could contribute to further investigations of bacterial distributions in environmental soil or water.

Specific nanoantibiotics for selective removal of antibiotic-resistant bacteria: New insights in bacterial imprinting based on interfacial biomimetic mineralization.

Antibiotic resistance has been a worsening global concern and selective elimination of antibiotic-resistant bacteria (ARB) while retaining the co-existed beneficial bacteria has been essential in environmental protection, which having attracted considerable interest. In this work, by integrating the whole cell imprinting and epitope imprinting strategy, magnetic bacterial imprinted polymers (BIPs) towards ARB were synthesized with interfacial biomimetic mineralization followed by a screening process. The binding data showed that the BIPs owned highly specific affinity towards the target bacteria. Taking advantage of this specific binding ability of BIPs, a two-step selective antimicrobial approach was developed. Remarkably, the BIP nanoantibiotics (nAbts) could efficiently destroy ARB without harming the beneficial bacteria. In comparison with the non-bacterial imprinted polymers, the biocompatible BIP nAbts showed a 12.5-fold increase in the survival percentage for the beneficial bacteria in wastewater. To the best of our knowledge, this is the first time that bacterial imprinting via interfacial biomimetic mineralization was developed, and also the first report of killing ARB without harming the beneficial bacteria in wastewater. We believe that this strategy provides a new insight into the design of novel affinity materials for the selective elimination of ARB in biological treatment for environmental protection.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application.

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

Poly(vinylidene fluoride)/partially alkylated poly(vinyl imidazole) interpolymer ultrafiltration membranes with intrinsic anti-biofouling and antifouling property for the removal of bacteria.

Bacterial contaminated water causes potential health issues. Conventional chlorine treatment has shortcomings of environmental hazards and chlorine adoptability by the bacterial cells. Ultrafiltration membrane can intercept bacterial species from feed water. Membrane having anti-biofouling/antifouling properties is needed for the removal of bacteria from feed water. Herein, interpolymer membranes with inherent antimicrobial activity and fouling release property have been prepared by the blend of poly(vinylidene fluoride) (PVDF), poly(vinyl pyrrolidone) and partially long chain alkylated (C12 chain) poly(vinyl imidazole) copolymer (PVIm-co-PVIm-C12) followed by cross-linking of the remaining VIm groups with an activated di-halide compound. The membranes obtain with copolymers of degree of alkyl substitution (DSC12) in the range of 0.75-0.85 and amount in the range of 0.9-3.5% w/w in the casting solutions exhibit good antimicrobial activity (>99 % of inhibition) and dynamic anti-biofouling property. The membrane prepared with 0.9% w/w of the copolymer (DSC12=0.85) shows higher flux recovery ratio (91 % for bacterial filtration and 88 % for protein filtration) compare to a pristine membrane (57 % for bacterial filtration and 58 % for protein filtration). The membrane is able to reject the bacteria completely. Use of small amount of copolymer and facile fabrication of stable anti-biofouling/antifouling membranes show potential for the purification of bacterial contaminated water.

Recent Advances in the Use of Mesoporous Silica Nanoparticles for the Diagnosis of Bacterial Infections.

Public awareness of infectious diseases has increased in recent months, not only due to the current COVID-19 outbreak but also because of antimicrobial resistance (AMR) being declared a top-10 global health threat by the World Health Organization (WHO) in 2019. These global issues have spiked the realization that new and more efficient methods and approaches are urgently required to efficiently combat and overcome the failures in the diagnosis and therapy of infectious disease. This holds true not only for current diseases, but we should also have enough readiness to fight the unforeseen diseases so as to avoid future pandemics. A paradigm shift is needed, not only in infection treatment, but also diagnostic practices, to overcome the potential failures associated with early diagnosis stages, leading to unnecessary and inefficient treatments, while simultaneously promoting AMR. With the development of nanotechnology, nanomaterials fabricated as multifunctional nano-platforms for antibacterial therapeutics, diagnostics, or both (known as "theranostics") have attracted increasing attention. In the research field of nanomedicine, mesoporous silica nanoparticles (MSN) with a tailored structure, large surface area, high loading capacity, abundant chemical versatility, and acceptable biocompatibility, have shown great potential to integrate the desired functions for diagnosis of bacterial infections. The focus of this review is to present the advances in mesoporous materials in the form of nanoparticles (NPs) or composites that can easily and flexibly accommodate dual or multifunctional capabilities of separation, identification and tracking performed during the diagnosis of infectious diseases together with the inspiring NP designs in diagnosis of bacterial infections.

Combining Inducible Lectin Expression and Magnetic Glyconanoparticles for the Selective Isolation of Bacteria from Mixed Populations.

The selective isolation of bacteria from mixed populations has been investigated in varied applications ranging from differential pathogen identification in medical diagnostics and food safety to the monitoring of microbial stress dynamics in industrial bioreactors. Selective isolation techniques are generally limited to the confinement of small populations in defined locations, may be unable to target specific bacteria, or rely on immunomagnetic separation, which is not universally applicable. In this proof-of-concept work, we describe a novel strategy combining inducible bacterial lectin expression with magnetic glyconanoparticles (MGNPs) as a platform technology to enable selective bacterial isolation from cocultures. An inducible mutant of the type 1 fimbriae, displaying the mannose-specific lectin FimH, was constructed in Escherichia coli allowing for "on-demand" glycan-binding protein presentation following external chemical stimulation. Binding to glycopolymers was only observed upon fimbrial induction and was specific for mannosylated materials. A library of MGNPs was produced via the grafting of well-defined catechol-terminal glycopolymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization to magnetic nanoparticles. Thermal analysis revealed high functionalization (≥85% polymer by weight). Delivery of MGNPs to cocultures of fluorescently labeled bacteria followed by magnetic extraction resulted in efficient depletion of type 1 fimbriated target cells from wild-type or afimbriate E. coli. Extraction efficiency was found to be dependent on the molecular weight of the glycopolymers utilized to engineer the nanoparticles, with MGNPs decorated with shorter Dopa-(ManAA)50 mannosylated glycopolymers found to perform better than those assembled from a longer Dopa-(ManAA)200 analogue. The extraction efficiency of fimbriated E. coli was also improved when the counterpart strain did not harbor the genetic apparatus for the expression of the type 1 fimbriae. Overall, this work suggests that the modulation of the genetic apparatus encoding bacterial surface-associated lectins coupled with capture through MGNPs could be a versatile tool for the extraction of bacteria from mixed populations.

Factors affecting sedimentational separation of bacteria from blood.

Rapid diagnosis of blood infections requires fast and efficient separation of bacteria from blood. We have developed spinning hollow disks that separate bacteria from blood cells via the differences in sedimentation velocities of these particles. Factors affecting separation included the spinning speed and duration, and disk size. These factors were varied in dozens of experiments for which the volume of separated plasma, and the concentration of bacteria and red blood cells (RBCs) in separated plasma were measured. Data were correlated by a parameter of characteristic sedimentation length, which is the distance that an idealized RBC would travel during the entire spin. Results show that characteristic sedimentation length of 20 to 25 mm produces an optimal separation and collection of bacteria in plasma. This corresponds to spinning a 12-cm-diameter disk at 3,000 rpm for 13 s. Following the spin, a careful deceleration preserves the separation of cells from plasma and provides a bacterial recovery of about 61 ± 5%.

Acoustofluidic bacteria separation.

Bacterial separation from human blood samples can help with the identification of pathogenic bacteria for sepsis diagnosis. In this work, we report an acoustofluidic device for label-free bacterial separation from human blood samples. In particular, we exploit the acoustic radiation force generated from a tilted-angle standing surface acoustic wave (taSSAW) field to separate E. coli from human blood cells based on their size difference. Flow cytometry analysis of the E. coli separated from red blood cells (RBCs) shows a purity of more than 96%. Moreover, the label-free electrochemical detection of the separated E. coli displays reduced non-specific signals due to the removal of blood cells. Our acoustofluidic bacterial separation platform has advantages such as label-free separation, high biocompatibility, flexibility, low cost, miniaturization, automation, and ease of in-line integration. The platform can be incorporated with an on-chip sensor to realize a point-of-care (POC) sepsis diagnostic device.

Rapid separation of bacteria from blood - Chemical aspects.

To rapidly diagnose infectious organisms causing blood sepsis, bacteria must be rapidly separated from blood, a very difficult process considering that concentrations of bacteria are many orders of magnitude lower than concentrations of blood cells. We have successfully separated bacteria from red and white blood cells using a sedimentation process in which the separation is driven by differences in density and size. Seven mL of whole human blood spiked with bacteria is placed in a 12-cm hollow disk and spun at 3000rpm for 1min. The red and white cells sediment more than 30-fold faster than bacteria, leaving much of the bacteria in the plasma. When the disk is slowly decelerated, the plasma flows to a collection site and the red and white cells are trapped in the disk. Analysis of the recovered plasma shows that about 36% of the bacteria is recovered in the plasma. The plasma is not perfectly clear of red blood cells, but about 94% have been removed. This paper describes the effects of various chemical aspects of this process, including the influence of anticoagulant chemistry on the separation efficiency and the use of wetting agents and platelet aggregators that may influence the bacterial recovery. In a clinical scenario, the recovered bacteria can be subsequently analyzed to determine their species and resistance to various antibiotics.

First Observation of Physically Capturing and Maneuvering Bacteria using Magnetic Clays.

A new class of nanohybrids composed of structurally exfoliated silicate platelets and magnetic iron oxide nanoparticles was synthesized and shown to be capable of capturing microbes in liquid microbiological media. Nanoscale silicate platelets with an approximate thickness of 1.0 nm were prepared from the naturally occurring mineral clays montmorillonite and mica; these clays yielded platelets with lateral dimensions on the order of 80-100 nm and 300-1000 nm, respectively. The magnetic Fe3O4 nanoparticles, approximately 8.3 nm in diameter, were coated in situ onto the silicates during the synthesis process, which involved the coprecipitation of aqueous Fe(2+)/Fe(3+) salts. Owing to the high surface area-to-volume ratios and the presence of ionically charged groups (i.e., ≡SiO(-)Na(+)), the silicate nanoplatelets exhibited intense noncovalent bonding forces between Fe3O4 nanoparticles and the surrounding microorganisms. The Fe3O4-on-nanoplatelet nanohybrids enabled the entrapment of bacterial cells in liquid microbiological media. These captured bacteria formed bacterial aggregates on the order of micrometers that became physically maneuverable under a magnetic field. This phenomenon was demonstrated with Staphylococcus aureus in liquid microbiological media by physically removing them using a magnetic bar; in two experimental examples, bacterial concentrations were reduced from 10(6) to 10(2) and from 10(4) to 10(0) CFU/mL (colony formation unit/mL con). Under a scanning electron microscope, these bacteria appeared to have rough and wrinkled surfaces due to the accumulated silicate platelets. Furthermore, the external application of a high-frequency magnetic field completely destroyed these aggregated microbes by the magnetically induced heat. Hence, the newly developed nanohybrids were shown to be viable for physically capturing microbes and also for potential hyperthermia treatment applications.

Pathogen enrichment device (PED) enables one-step growth, enrichment and separation of pathogen from food matrices for detection using bioanalytical platforms.

The bottleneck for accurate detection of foodborne pathogens is separation of target analytes from complex food matrices. Currently used sample preparation methods are cumbersome, arduous and lengthy; thus, a user-friendly system is desirable. A hand-held sample preparation system designated pathogen enrichment device (PED) was built that contains a growth chamber, filters, and an ion exchange cartridge to deliver bacteria directly onto the detection platforms. Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes were used as model pathogens. Spinach, ground beef, hotdogs, and eggs were used as model foods to evaluate PED performance, and results were compared with traditional bag enrichment method. Bacterial cells were inoculated at 1, 10, and 100 CFU/g of the sample and enriched in PED using appropriate pathogen-specific selective enrichment broths. The bacterial cell counts in both PED and stomacher-bag were comparable and the pH in PED-recovered cell suspension was close to neutral whereas the pH of cell suspension in the stomacher-bag was slightly acidic. The bacterial recovery from the PED was 79-100% and was directly detected by lateral-flow immunoassay (LFIA), quantitative PCR (qPCR) and light scattering sensor with sample-to-result time of 8-24h with a detection limit of 1CFU/g. In qPCR, the amplified PCR products appeared in 4-5 cycles earlier with PED-enriched cultures compared to the cultures enriched in stomacher-bag. The hand-held PED proved to be a one-step procedure for enrichment and recovery of homogenous particle-free bacterial cells for detection using immunological, molecular or biosensor-based platforms.