Chemical sensors for the early diagnosis of bacterial resistance to β-lactam antibiotics

β-Lactamases are bacterial enzymes that inactivate β-lactam antibiotics and, as such, are the most prevalent cause of antibiotic resistance in Gram-negative bacteria. The ever-increasing production and worldwide dissemination of bacterial strains producing carbapenemases is currently a global health concern. These enzymes catalyze the hydrolysis of carbapenems - the β-lactam antibiotics with the broadest spectrum of activity that are often considered as drugs of last resort. The incidence of carbapenem-resistant pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii and carbapenemase or extended spectrum beta-lactamase (ESBL)-producing Enterobacterales, which are frequent in clinical settings, is worrisome since, in some cases, no therapies are available. These include all metallo-β-lactamases (VIM, IMP, NDM, SMP, and L1), and serine-carbapenemases of classes A (KPC, SME, IMI, and GES), and of classes D (OXA-23, OXA-24/40, OXA-48 and OXA-58). Consequently, the early diagnosis of bacterial strains harboring carbapenemases is a pivotal task in clinical microbiology in order to track antibiotic bacterial resistance and to improve the worldwide management of infectious diseases. Recent research efforts on the development of chromogenic and fluorescent chemical sensors for the specific and sensitive detection and quantification of β-lactamase production in multidrug-resistant pathogens are summarized herein. Studies to circumvent the main limitations of the phenotypic and molecular methods are discussed. Recently reported chromogenic and fluorogenic cephalosporin- and carbapenem-based β-lactamase substrates will be reviewed as alternative options to the currently available nitrocefin and related compounds, a chromogenic cephalosporin-based reagent widely used in clinical microbiology laboratories. The scope of these new chemical sensors, along with the synthetic approaches to synthesize them, is also summarized.

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.

Advances in the detection of β-lactamase: A review

β-lactamase, an enzyme secreted by bacteria, is the main resistant mechanism of Gram-negative bacteria to β-lactam antibiotics. The resistance of bacteria to β-lactam antibiotics can be evaluated by testing the activity of β-lactamase. Traditional phenotypic detection is a golden principle, but it is time-consuming. In recent years, many new methods have emerged, which improve the efficiency by virtue of their sensitivity, low cost, easy operation, and other advantages. In this paper, we systematically review these researches and emphasize their limits of detection, sample operation, and test duration. Noteworthily, some detection systems can identify the β-lactamase subtype conveniently. We mainly divide these tests into three categories to elaborate their characteristics and application status. Both advantages and disadvantages of these methods are discussed. Additionally, we analyze the recent 5 years published researches to predict the trend of development in this field.

Culture-Independent Multiplexed Detection of Drug-Resistant Bacteria Using Surface-Enhanced Raman Scattering

The rapid and accurate detection of bacteria resistance to β-lactam antibiotics is critical to inform optimal treatment and prevent overprescription of potent antibiotics. Here, we present a fast, culture-independent method for the detection of extended-spectrum β-lactamases (ESBLs) using surface-enhanced Raman scattering (SERS). The method uses Raman probes that release sulfur-based Raman active molecules in the presence of β-lactamases. The released thiol molecules can be captured by gold nanoparticles, leading to amplified Raman signals. A broad-spectrum cephalosporin probe R1G and an ESBL-specific probe R3G are designed to enable duplex detection of bacteria expressing broad-spectrum β-lactamases or ESBLs with a detection limit of 103 cfu/mL in 1 h incubation. Combined with a portable Raman microscope, our culturing-free SERS assay has reduced screening time to 1.5 h without compromising sensitivity and specificity.

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.

Dismantling the bacterial glycocalyx: Chemical tools to probe, perturb, and image bacterial glycans

The bacterial glycocalyx is a quintessential drug target comprised of structurally distinct glycans. Bacterial glycans bear unusual monosaccharide building blocks whose proper construction is critical for bacterial fitness, survival, and colonization in the human host. Despite their appeal as therapeutic targets, bacterial glycans are difficult to study due to the presence of rare bacterial monosaccharides that are linked and modified in atypical manners. Their structural complexity ultimately hampers their analytical characterization. This review highlights recent advances in bacterial chemical glycobiology and focuses on the development of chemical tools to probe, perturb, and image bacterial glycans and their biosynthesis. Current technologies have enabled the study of bacterial glycosylation machinery even in the absence of detailed structural information.

A dual-caged resorufin probe for rapid screening of infections resistant to lactam antibiotics

The alarming increase of antimicrobial resistance urges rapid diagnosis and pathogen specific infection management. This work reports a rapid screening assay for pathogenic bacteria resistant to lactam antibiotics. We designed a fluorogenic N-cephalosporin caged 3,7-diesterphenoxazine probe CDA that requires sequential activations to become fluorescent resorufin. A series of studies with recombinant β-lactamases and clinically prevalent pathogens including Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Serratia marcescens demonstrated that CDA possessed superior sensitivity in reporting the activity of β-lactamases including cephalosporinases and carbapenemases. After a simple filtration, lactam-resistant bacteria in urine samples could be detected at 103 colony-forming units per milliliter within 2 hours.

Chemiluminescence Detection of Hydrogen Sulfide Release by β-Lactamase-Catalyzed β-Lactam Biodegradation: Unprecedented Pathway for Monitoring β-Lactam Antibiotic Bacterial Resistance

β-Lactamase positive bacteria represent a growing threat to human health because of their resistance to commonly used antibiotics. Therefore, development of new diagnostic methods for identification of β-lactamase positive bacteria is of high importance for monitoring the spread of antibiotic-resistant bacteria. Here, we report the discovery of a new biodegradation metabolite (H2S), generated through β-lactamase-catalyzed hydrolysis of β-lactam antibiotics. This discovery directed us to develop a distinct molecular technique for monitoring bacterial antibiotic resistance. The technique is based on a highly efficient chemiluminescence probe, designed for detection of the metabolite, hydrogen sulfide, that is released upon biodegradation of β-lactam by β-lactamases. Such an assay can directly indicate if antibiotic bacterial resistance exists for a certain examined β-lactam. The assay was successfully demonstrated for five different β-lactam antibiotics and eight β-lactam resistant bacterial strains. Importantly, in a functional bacterial assay, our chemiluminescence probe was able to clearly distinguish between a β-lactam resistant bacterial strain and a sensitive one. As far as we know, there is no previous documentation for such a biodegradation pathway of β-lactam antibiotics. Bearing in mind the data obtained in this study, we propose that hydrogen sulfide should be considered as an emerging β-lactam metabolite for detection of bacterial resistance.

Fluorescent antibiotics for real-time tracking of pathogenic bacteria

The harm of pathogenic bacteria to humans has promoted extensive research on physiological processes of pathogens, such as the mechanism of bacterial infection, antibiotic mode of action, and bacterial antimicrobial resistance. Most of these processes can be better investigated by timely tracking of fluorophore-derived antibiotics in living cells. In this paper, we will review the recent development of fluorescent antibiotics featuring the conjugation with various fluorophores, and focus on their applications in fluorescent imaging and real-time detection for various physiological processes of bacteria in vivo.

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Profiles of Fluorophores-derived Antibiotics in Development.

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Discussing the influence on antibiotic activity after conjugating fluorophore.

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Fluorescent Tracking to better understand physiological processes of Pathogenic bacteria.

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Live-Cell imaging to investigate bacteria in their native environment.

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.

Performance of a Novel Fluorogenic Assay for Detection of Carbapenemase-Producing Enterobacteriaceae from Bacterial Colonies and Directly from Positive Blood Cultures

Rapid and accurate detection of carbapenemase-producing Enterobacteriaceae (CPE) is critical for appropriate treatment and infection control. We compared a rapid fluorogenic assay using a carbapenem-based fluorogenic probe with other phenotypic assays: modified carbapenem inactivation method (mCIM), Carba NP test (CNP), and carbapenemase inhibition test (CIT). A total of 217 characterized isolates of Enterobacteriaceae were included as follows: 63 CPE; 48 non-carbapenemase-producing carbapenem-resistant Enterobacteriaceae (non-CP-CRE); 53 extended-spectrum β-lactamase producers; and 53 third-generation-cephalosporin-susceptible isolates. The fluorogenic assay using bacterial colonies (Fluore-C) was conducted by lysing the isolates followed by centrifugation and mixing the supernatant with fluorogenic probe. In addition, for the fluorogenic assay using spiked blood culture bottles (Fluore-Direct), pellets were obtained via the saponin preparation method, which can directly identify the pathogens using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The fluorescence signal was measured over 50 min using a fluorometer. The fluorescent signal of CPE was significantly higher than that of non-CPE in both Fluore-C (median relative fluorescence units [RFU] [range], 5,814 [240 to 32,009] versus 804 [36 to 2,480], respectively; P < 0.0001) and Fluore-Direct (median RFU [range], 10,355 [1,689 to 31,463] versus 1,068 [428 to 2,155], respectively; P < 0.0001) tests. Overall, positive and negative percent agreements of Fluore-C, mCIM, CNP, CIT, and Fluore-Direct were 100% and 98.7%, 98.3% and 97.5%, 88.1% and 100%, 96.4% and 98.7%, and 98.3% and 98.1%, respectively. The relatively lower positive percent agreement (PPA) of CNP was mainly observed in OXA-type CPE. The fluorogenic assay showed excellent performance with bacterial colonies and also directly from positive blood cultures. We included many non-CP-CRE isolates for strict evaluation. The fluorogenic assay will be a useful tool for clinical microbiology laboratories.

Development of carbapenem-based fluorogenic probes for the clinical screening of carbapenemase-producing bacteria

This report describes the synthesis of a library of fluorogenic carbapenemase substrates consisting of carbapenem derivatives, fluorescence dyes, and active cleavable linkers and their evaluation for specifically detecting carbapenemase-producing organisms (CPOs). We synthesized a series of compounds having three different types of linkers such as benzyl ether, carbamate, and amine using hydroxymethyl carbapenem 7a and hydroxyallyl carbapenem 7b as key intermediates. Probe 1b exhibited high stability and a prompt turn-on fluorescence signal upon hydrolysis by carbapenemases. In particular, the screening of clinical samples indicated that the probe 1b exhibited excellent selectivity to the CPOs over other β-lactamases or non-carbapenemase producing bacteria, which may be of clinical use for the rapid and accurate detection of CPOs for timely diagnosis and treatment.

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.

Fluorescent Antibiotics: New Research Tools to Fight Antibiotic Resistance

Better understanding how multidrug-resistant (MDR) bacteria can evade current and novel antibiotics requires a better understanding of the chemical biology of antibiotic action. This necessitates using new tools and techniques to advance our knowledge of bacterial responses to antibiotics, ideally in live cells in real time, to selectively investigate bacterial growth, division, metabolism, and resistance in response to antibiotic challenge. In this review, we discuss the preparation and biological evaluation of fluorescent antibiotics, focussing on how these reporters and assay methods can help elucidate resistance mechanisms. We also examine the potential utility of such probes for real-time in vivo diagnosis of infections.

A simple design of fluorescent probes for indirect detection of β-lactamase based on AIE and ESIPT processes

A fluorescent probe with both AIE and ESIPT characteristics has been developed for β-lactamase based on an indirect approach.