Rapid Detection of Bacterial Resistance to β-Lactam Antibiotics with a Relay-Response Chemiluminescence Assay

Bacterial resistance caused by β-lactamases has been a major threat to public health around the world, seriously weakening the efficacy of β-lactam antibiotics, the most widely used therapeutic agents against infectious diseases. To detect the bacterial resistance to β-lactam antibiotics, particularly specific type of β-lactam antibiotics, in a rapid manner, we report herein a relay-response chemiluminescence assay. This assay mainly consists of two reagents: a β-lactam-caged thiophenol and a thiophenol-sensitive chemiluminescence reporter, both of which are synthetically feasible. The selective hydrolysis of β-lactam by β-lactamase leads to the releasing of free thiophenol, which then triggers the emission of a chemiluminescence signal in a relay manner. Three thiophenol-caged β-lactams, structural analogues of cephalothin, cefotaxime, and meropenem, respectively, have been synthesized. And the application of this assay with these analogues of β-lactam antibiotics allows fast detection of β-lactamase-expressing resistant bacteria and, more impressively, provides detailed information on the resistant scope of bacteria.

Preparation of gelatin-chitosan bilayer film loaded citral nanoemulsion as pH and enzyme stimuli-responsive antibacterial material for food packaging

The responsive release of enzymes, pH, temperature, light and other stimuli is an effective means to reduce the loss of volatile active substances and control the release of active ingredients. The purpose of this study is to design a simple and rapid method to synthesize a multifunctional bilayer membrane, which has good mechanical properties, long-lasting pH and enzyme dual sensitive sustained release properties, and excellent antibacterial activity. The citral nanoemulsion was prepared by ultrasonic method, then the chitosan solution loaded with nanoemulsion was assembled on the gelatin film, and the uniform and smooth gelatin-chitosan bilayer film was successfully prepared. Compared with the control group, the bilayer film loaded with nanoemulsion showed better barrier performance, mechanical properties and antibacterial activity.

Bioluminogenic Probe for Rapid, Ultrasensitive Detection of β-Lactam-Resistant Bacteria

Increasingly difficult-to-treat infections by antibiotic-resistant bacteria have become a major public health challenge. Rapid detection of common resistance mechanisms before empiric antibiotic usage is essential for optimizing therapeutic outcomes and containing further spread of resistance to antibiotics among other bacteria. Herein, we present a bioluminogenic probe, D-Bluco, for rapid detection of β-lactamase activity in viable pathogenic bacteria. D-Bluco is a pro-luciferin caged by a β-lactamase-responsive cephalosporin structure and further conjugated with a dabcyl quencher. The caging and quenching significantly decreased the initial background emission and increased the signal-to-background ratio by more than 1200-fold. D-Bluco was shown to detect a broad range of β-lactamases at the femtomolar level. An ultrasensitive RAPID bioluminescence assay using D-Bluco can detect 102 to 103 colony forming unit per milliliter (cfu/mL) of β-lactamase-producing Enterobacterales in urine samples within 30 min. The high sensitivity and rapid detection make the assay attractive for the use of point-of-care diagnostics for lactam-resistant pathogens.

Nanotechnology: a contemporary therapeutic approach in combating infections from multidrug-resistant bacteria

In the 20th century, the discovery of antibiotics played an essential role in the fight against infectious diseases, including meningitis, typhoid fever, pneumonia and Mycobacterium tuberculosis. The development of multidrug resistance in microflora due to improper antibiotic use created significant public health issues. Antibiotic resistance has increased at an alarming rate in the past few decades. Multidrug-resistant bacteria (superbugs) such as methicillin-resistant Staphylococcus aureus (MRSA) as well as drug-resistant tuberculosis pose serious health implications. Despite the continuous increase in resistant microbes, the discovery of novel antibiotics is constrained by the cost and complexities of discovery of drugs. The nanotechnology has given new hope in combating this problem. In the present review, recent developments in therapeutics utilizing nanotechnology for novel antimicrobial drug development are discussed. The nanoparticles of silver, gold and zinc oxide have proved to be efficient antimicrobial agents against multidrug-resistant Klebsiella, Pseudomonas, Escherichia Coli and MRSA. Using nanostructures as carriers for antimicrobial agents provides better bioavailability, less chances of sub-therapeutic drug accumulation and less drug-related toxicity. Nanophotothermal therapy using fullerene and antibody functionalized nanostructures are other strategies that can prove to be helpful.

β-Lactamase-Mediated Fragmentation: Historical Perspectives and Recent Advances in Diagnostics, Imaging, and Antibacterial Design

The discovery of β-lactam (BL) antibiotics in the early 20th century represented a remarkable advancement in human medicine, allowing for the widespread treatment of infectious diseases that had plagued humanity throughout history. Yet, this triumph was followed closely by the emergence of β-lactamase (BLase), a bacterial weapon to destroy BLs. BLase production is a primary mechanism of resistance to BL antibiotics, and the spread of new homologues with expanded hydrolytic activity represents a pressing threat to global health. Nonetheless, researchers have developed strategies that take advantage of this defense mechanism, exploiting BLase activity in the creation of probes, diagnostic tools, and even novel antibiotics selective for resistant organisms. Early discoveries in the 1960s and 1970s demonstrating that certain BLs expel a leaving group upon BLase cleavage have spawned an entire field dedicated to employing this selective release mechanism, termed BLase-mediated fragmentation. Chemical probes have been developed for imaging and studying BLase-expressing organisms in the laboratory and diagnosing BL-resistant infections in the clinic. Perhaps most promising, new antibiotics have been developed that use BLase-mediated fragmentation to selectively release cytotoxic chemical "warheads" at the site of infection, reducing off-target effects and allowing for the repurposing of putative antibiotics against resistant organisms. This Review will provide some historical background to the emergence of this field and highlight some exciting recent reports that demonstrate the promise of this unique release mechanism.

Ortho-Phosphinoarenesulfonamide-Mediated Staudinger Reduction of Aryl and Alkyl Azides

Conventional Staudinger reductions of organic azides are sluggish with aryl or bulky aliphatic azides. In addition, Staudinger reduction usually requires a large excess of water to promote the decomposition of the aza-ylide intermediate into phosphine oxide and amine products. To overcome the challenges above, we designed a novel triaryl phosphine reagent 2c with an ortho-SO₂NH₂ substituent. Herein, we report that such phosphine reagents are able to mediate the Staudinger reduction of both aryl and alkyl azides in either anhydrous or wet solvents. Good to excellent yields were obtained in all cases (even at a diluted concentration of 0.01 M). The formation of B-TAP, a cyclic aza-ylide, instead of phosphine oxide, eliminates the requirement of water in the Staudinger reduction. In addition, computational studies disclose that the intramolecular protonation of the aza-ylide by the ortho-SO₂NH₂ group is kinetically favorable and responsible for the acceleration of Staudinger reduction of the aryl azides.

Stimuli-Responsive Antibacterial Materials: Molecular Structures, Design Principles, and Biomedical Applications

Infections are regarded as the most severe complication associated with human health, which are urgent to be solved. Stimuli-responsive materials are appealing therapeutic platforms for antibacterial treatments, which provide great potential for accurate theranostics. In this review, the advantages, the response mechanisms, and the key design principles of stimuli-responsive antibacterial materials are highlighted. The biomedical applications, the current challenges, and future directions of stimuli-responsive antibacterial materials are also discussed. First, the categories of stimuli-responsive antibacterial materials are comprehensively itemized based on different sources of stimuli, including external physical environmental stimuli (e.g., temperature, light, electricity, salt, etc.) and bacterial metabolites stimuli (e.g., acid, enzyme, redox, etc.). Second, structural characteristics, design principles, and biomedical applications of the responsive materials are discussed, and the underlying interrelationships are revealed. The molecular structures and design principles are closely related to the sources of stimuli. Finally, the challenging issues of stimuli-responsive materials are proposed. This review will provide scientific guidance to promote the clinical applications of stimuli-responsive antibacterial materials.

Structure of Self-assembled Peptide Determines the Activity of Aggregation-Induced Emission Luminogen-Peptide Conjugate for Detecting Alkaline Phosphatase

The unique property of turning on their fluorescence after aggregation or assembly makes aggregation-induced emission luminogens (AIEgens) ideal luminescent molecules for the construction of self-assembled peptide-based nanoprobes. However, the characteristic highly twisted or propeller-shaped molecular conformation of AIEgens tends to prevent the assembly of AIEgen-peptides. Here, we show that (i) the distance between tetraphenylethene (TPE) and assembled peptides should not be too far (less than five glycines), otherwise the self-assembly of peptides cannot limit the intramolecular rotation of conjugated TPE and the luminous efficiency of TPE-peptide to alkaline phosphatase (ALP) will decrease; (ii) properly increasing the number of amino acids with self-assembly ability (three phenylalanines) can improve their ALP-responsive self-assembly and luminescence ability; (iii) the strategy of co-assembly with a non-AIEgen-capped self-assembled peptide is a simple and effective way to realize the efficient assembly and luminescence of AIEgen-peptides; and (iv) the hydrophilic and hydrophobic balance of the probe should always be considered in the construction of an efficient AIEgen-peptide probe. In addition, AIEgen-peptide probes show good selectivity and sensitivity for ALP detection both in vitro and in live bacteria. These insights illustrated here are crucial for guiding the design of AIEgen-conjugated supramolecular materials, especially for the construction of AIEgen-peptides, for enzymes detection, biomarker imaging, diseases therapy, and other biomedical fields.

Enzyme-responsive strategy as a prospective cue to construct intelligent biomaterials for disease diagnosis and therapy

Stimuli-responsive materials have been widely studied and applied in biomedical field. Under the stimulation of enzymes, the enzyme-responsive materials (ERMs) can be triggered to change their structures, properties and functions....

Small-molecule fluorescent probes: big future for specific bacterial labeling and infection detection

Bacterial infections remain a global healthcare problem that is particularly attributed to the spread of antibiotic resistance and the evolving pathogenicity. Accurate and swift approaches for infection diagnosis are urgently needed to facilitate antibiotic stewardship and effective medical treatment. Direct optical imaging for specific bacterial labeling and infection detection offers an attractive prospect of precisely monitoring the infectious disease status and therapeutic response in real time. This feature article focuses on the recent advances of small-molecule probes developed for fluorescent imaging of bacteria and infection, which covers the probe design, responsive mechanisms and representative applications. In addition, the perspective and challenges to advance small-molecule fluorescent probes in the field of rapid drug-resistant bacterial detection and clinical diagnosis of bacterial infections are discussed. We envision that the continuous advancement and clinical translations of such a technique will have a strong impact on future anti-infective medicine.

Specific detection of IMP-1 β-lactamase activity using a trans cephalosporin-based fluorogenic probe

A fluorogenic probe for the specific detection of IMP-1 β-lactamase activity has been developed. This imaging reagent features a unique trans-acetylamino cephalosporin as an enzymatic recognition moiety, exhibiting excellent selectivity to IMP-1 β-lactamase over other β-lactamases, including serine- and metallo-β-lactamases. The selective activation of the probe by IMP-1 β-lactamase leads to over 30-fold enhancement in the fluorescence intensity, which allows enzyme activity to be reported with high sensitivity.

Tailoring metal-organic frameworks-based nanozymes for bacterial theranostics

Nanozymes are next-generation artificial enzymes having distinguished features such as cost-effective, enhanced surface area, and high stability. However, limited selectivity and moderate activity of nanozymes in the biochemical environment hindered their usage and encouraged researchers to seek alternative catalytic materials. Recently, metal-organic frameworks (MOFs) characterized by distinct crystalline porous structures with large surface area, tunable pores, and uniformly dispersed active sites emerged, that filled the gap between natural enzymes and nanozymes. Moreover, by selecting suitable metal ions and organic linkers, MOFs can be designed for effective bacterial theranostics. In this review, we briefly presented the design and fabrication of MOFs. Then, we demonstrated the applications of MOFs in bacterial theranostics and their safety considerations. Finally, we proposed the major obstacles and opportunities for further development in research on the interface of nanozymes and MOFs. We expect that MOFs based nanozymes with unique physicochemical and intrinsic enzyme-mimicking properties will gain broad interest in both fundamental research and biomedical applications.

Screening aptamers for serine β-lactamase-expressing bacteria with Precision-SELEX

Klebsiella pneumoniae carbapenemase 2 (KPC-2) is a serine β-lactamase that can hydrolyze almost all β-lactam antibiotics. The drug resistant problem of bacteria expressing carbapenemases is currently a global problem, therefore, rapid and specific detection of pathogenic bacteria is urgent. In order to obtain an aptamer that can specifically recognize bacteria expressing KPC-2, we have established a method called Precision-SELEX. Precision-SELEX combined protein SELEX and bacterium SELEX. In this method, KPC-2 was used as a target protein, and Escherichia coli expressing KPC-2 (KPC-2 E. coli) was used as a target bacterium. After precision-SELEX, the same aptamer named XK-10 that can recognize KPC-2 and KPC-2 E. coli was obtained while the screening process could be shortened to 4 rounds. Dissociation equilibrium constants were calculated as 0.81 nM by SPR. In addition, XK-10 could specifically bind to KPC-2 E. coli, which was confirmed through flow cytometry and molecular Docking Simulations. The high-content imaging method could detect KPC-2 E. coli. In all, the Precision-SELEX provides an accurate and efficient method to screening aptamers for bacteria.

Fluorescent Mesoporous Nanoparticles for β-Lactamase Screening Assays

We present a sensitive and rapid screening method for the determination of β-lactamase activity of antibiotic-resistant bacteria, by designing a pH-sensitive fluorescent dye-doped mesoporous silica nanoparticle encapsulated with penicillin G as a substrate. When penicillin G was hydrolysed by β-lactamase and converted into penicilloic acid, the acidic environment resulted in fluorescence quenching of the dye. The dye-doped mesoporous nanoparticles not only enhanced the β-lactamase-catalyzed reaction rate but also stablized the substrate, penicillin G, which degrades into penicilloic acid in a water solution without β-lactamase. Twentyfive clinical bacterial samples were tested and the antibiotic resistant and susceptible strains were identified. The proposed method may detect the presence of β -lactamases of clinically relevant samples in less than 1 hour. Moreover, the detection limit of β-lactamase activity was as low as 7.8×10-4 U/mL, which was determined within two hours.

β-Lactamase triggered visual detection of bacteria using cephalosporin functionalized biomaterials

We report the conjugation of a chromogenic cephalosporin β-lactamase (βL) substrate to polymers and integration into biomaterials for facile, visual βL detection. Identification of these bacterial enzymes, which are a leading cause of antibiotic resistance, is critical in the treatment of infectious diseases. The βL substrate polymer conjugate undergoes a clear to deep yellow color change upon incubation with common pathogenic Gram-positive and Gram-negative bacteria species. We have demonstrated the feasibility of formulating hydrogels with the βL substrate covalently tethered to a poly(ethylene glycol) (PEG) polymer matrix, exhibiting a visible color change in the presence of βLs. This approach has the potential to be used in diagnostic biomaterials for point-of-care detection of βL-producing bacteria, helping combat the spread of drug resistant microbes.

Fluorogenic Probes/Inhibitors of β-Lactamase and their Applications in Drug-Resistant Bacteria

β-Lactam antibiotics are generally perceived as one of the greatest inventions of the 20^th century, and these small molecular compounds have saved millions of lives. However, upon clinical application of antibiotics, the β-lactamase secreted by pathogenic bacteria can lead to the gradual development of drug resistance. β-Lactamase is a hydrolase that can efficiently hydrolyze and destroy β-lactam antibiotics. It develops and spreads rapidly in pathogens, and the drug-resistant bacteria pose a severe threat to human health and development. As a result, detecting and inhibiting the activities of β-lactamase are of great value for the rational use of antibiotics and the treatment of infectious diseases. At present, many specific detection methods and inhibitors of β-lactamase have been developed and applied in clinical practice. In this Minireview, we describe the resistance mechanism of bacteria producing β-lactamase and further summarize the fluorogenic probes, inhibitors of β-lactamase, and their applications in the treatment of infectious diseases. It may be valuable to design fluorogenic probes with improved selectivity, sensitivity, and effectiveness to further identify the inhibitors for β-lactamases and eventually overcome bacterial resistance.

A novel fluorescent probe for the detection of AmpC beta-lactamase and the application in screening beta-lactamase inhibitors

The rapid detection of β-lactamases (Blas) and effective screening of Bla inhibitors are critically important and urgent for solving antibiotic resistance and improving precision medicine. Here a novel fluorescent probe CDC-559 was designed and synthesized, which can be used for the selective and direct detection of AmpC Blas. More importantly, it can realize screening the Bla inhibitors with sulbactam sodium and tazobactam as model compounds, and the half-maximal inhibitory concentration are 0.279 μM and 0.053 μM, respectively. CDC-559 can be applied not only to examine the resistance of bacterial strains, but also to categorize its mode of action specifically, which is consistent with the essential result of the Blas. The research suggests that CDC-559 probe has tremendous potential in the rapid detection of AmpC Blas as well as the strains with AmpC-encoded gene, which is instructive in promoting better antibiotic stewardship practices and developments.

A minor structure modification serendipitously leads to a highly carbapenemase-specific fluorogenic probe

Reported herein is a fluorogenic probe for the detection of carbapenemase activity. This reagent features carbapenem as an enzyme recognition motif and a carbon-carbon double bond between carbapenem and the fluorophore, exhibiting high specificity to all carbapenemases, including metallo carbapenemases and serine carbapenemases, over other β-lactamases.

Colorimetric Band-aids for Point-of-Care Sensing and Treating Bacterial Infection

Sensing bacterial infections and monitoring drug resistance are very important for the selection of treatment options. However, the common methods of sensing resistance are limited by time-consuming, the requirement for professional personnel, and expensive instruments. Moreover, the abuse of antibiotics causes the accelerated process of bacterial resistance. Herein, we construct a portable paper-based band-aid (PBA) which implements a selective antibacterial strategy after sensing of drug resistance. The colors of PBA indicate bacterial infection (yellow) and drug resistance (red), just like a bacterial resistance colorimetric card. On the basis of color, antibiotic-based chemotherapy and Zr-MOF PCN-224-based photodynamic therapy (PDT) are used on site to treat sensitive and resistant strains, respectively. Eventually, it takes 4 h to sense, and the limit of detection is 10⁴ CFU/mL for drug-resistant E. coli. Compared with traditional PDT-based antibacterial strategies, our design can alleviate off-target side effects, maximize therapeutic efficacy, and track the drug resistance in real time with the naked eye. This work develops a new way for the rational use of antibiotics. Given the low cost and easy operation of this point-of-care device, it can be developed for practical applications.

Highly selective and wash-free visualization of resistant bacteria with a relebactam-derived fluorogenic probe

An unprecedented relebactam-based fluorogenic probe is reported for the wash-free imaging of resistant bacteria.

Folic acid-modified mesoporous silica nanoparticles with pH-responsiveness loaded with Amp for an enhanced effect against anti-drug-resistant bacteria by overcoming efflux pump systems

Efflux pump system-mediated bacterial multidrug resistance is one of the main causes of antibiotic failure. Therefore, it is necessary to develop a novel nanocarrier that could effectively inhibit drug-resistant bacteria by increasing the intake and retention time of antibiotics. Herein, we constructed a pH-responsive nanocarrier (MSN@FA@CaP@FA) with double folic acid (FA) and calcium phosphate (CaP) covered on the surface of mesoporous silica (MSN) by electrostatic attraction and biomineralization, respectively. Afterward, loading the nanocomposites with ampicillin (Amp) effectively increased the uptake and reduced the efflux effect in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by the specific targeting of FA. Moreover, Amp-MSN@FA@CaP@FA could specifically transport Amp to the bacterial infection site. Similarly, antibacterial experiments revealed that the Amp-MSN@FA@CaP@FA could significantly enhance the activity of Amp for inhibiting drug-resistant bacteria, without producing drug resistance. Additionally, the Amp-MSN@FA@CaP@FA could reduce the content of protein and inhibit the protein activity in drug-resistant bacteria, so that it destroyed the bacterial membrane and led to the bacteria death. In vivo antibacterial experiments showed that the Amp-MSN@FA@CaP@FA could effectively reduce the mortality of drug-resistant E. coli infection and promote wound healing of drug-resistant S. aureus infection. In summary, Amp-MSN@FA@CaP@FA has a potential for application in sustained-release nanostructures and to inhibit drug-resistant bacteria.

A core-shell nanoparticle-peptide@metal-organic framework as pH and enzyme dual-recognition switch for stepwise-responsive imaging in living cells

A core-shell nanostructure is fabricated with a pH-sensitive metal-organic framework shell and a peptide functionalized gold nanoparticle core via a mild synthetic route. The nanostructure can be applied as a dual-recognition switch in response to an acidic environment and enzyme activity, sequentially, leading to a stepwise-responsive strategy for imaging lysosomal cathepsin B.

Unique Fluorescent Imaging Probe for Bacterial Surface Localization and Resistant Enzyme Imaging

Emergence of antibiotic bacterial resistance has caused serious clinical issues worldwide due to increasingly difficult treatment. Development of a specific approach for selective visualization of resistant bacteria will be highly significant for clinical investigations to promote timely diagnosis and treatment of bacterial infections. In this article, we present an effective method that not only is able to selectively recognize drug resistant AmpC β-lactamases enzyme but, more importantly, is able to interact with bacterial cell wall components, resulting in a desired localization effect on the bacterial surface. A unique and specific enzyme-responsive cephalosporin probe (DFD-1) has been developed for the selective recognition of resistance bacteria AmpC β-lactamase, by employing fluorescence resonance energy transfer with an "off-on" bioimaging. To achieve the desired localization, a lipid-azide conjugate (LA-12) was utilized to facilitate its penetration into the bacterial surface, followed by copper-free click chemistry. This enables the probe DFD-1 to be anchored onto the cell surface. In the presence of AmpC enzymes, the cephalosporin β-lactam ring on DFD-1 will be hydrolyzed, leading to the quencher release, thus generating fluorescence for real-time resistant bacterial screening. More importantly, the bulky dibenzocyclooctyne group in DFD-1 allowed selective recognition toward the AmpC bacterial enzyme instead of its counterpart ( e.g., TEM-1 β-lactamase). Both live cell imaging and cell cytometry assays showed the great selectivity of DFD-1 to drug resistant bacterial pathogens containing the AmpC enzyme with significant fluorescence enhancement (∼67-fold). This probe presented promising capability to selectively localize and screen for AmpC resistance bacteria, providing great promise for clinical microbiological applications.

Novel Self-assembled Organic Nanoprobe for Molecular Imaging and Treatment of Gram-positive Bacterial Infection

Background: Increasing bacterial infections as well as a rise in bacterial resistance call for the development of novel and safe antimicrobial agents without inducing bacterial resistance. Nanoparticles (NPs) present some advantages in treating bacterial infections and provide an alternative strategy to discover new antibiotics. Here, we report the development of novel self-assembled fluorescent organic nanoparticles (FONs) with excellent antibacterial efficacy and good biocompatibility. Methods: Self-assembly of 1-(12-(pyridin-1-ium-1-yl)dodecyl)-4-(1,4,5-triphenyl-1H-imidazol-2-yl)pyridin-1-ium (TPIP) in aqueous solution was investigated using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The bacteria were imaged under a laser scanning confocal microscope. We evaluated the antibacterial efficacy of TPIP-FONsin vitro using sugar plate test. The antimicrobial mechanism was explored by SEM. The biocompatibility of the nanoparticles was examined using cytotoxicity test, hemolysis assay, and histological staining. We further tested the antibacterial efficacy of TPIP-FONsin vivo using the S. aureus-infected rats. Results: In aqueous solution, TPIP could self-assemble into nanoparticles (TPIP-FONs) with characteristic aggregation-induced emission (AIE). TPIP-FONs could simultaneously image gram-positive bacteria without the washing process. In vitro antimicrobial activity suggested that TPIP-FONs had excellent antibacterial activity against S. aureus (MIC = 2.0 µg mL^-1). Furthermore, TPIP-FONs exhibited intrinsic biocompatibility with mammalian cells, in particular, red blood cells. In vivo studies further demonstrated that TPIP-FONs had excellent antibacterial efficacy and significantly reduced bacterial load in the infectious sites. Conclusion: The integrated design of bacterial imaging and antibacterial functions in the self-assembled small molecules provides a promising strategy for the development of novel antimicrobial nanomaterials.

Branched peptides for enzymatic supramolecular hydrogelation

The use of protease (e.g., enterokinase) to cut branched peptides generates supramolecular hydrogels, opening a new way to explore soft materials for biomedicine.