A nitrocefin-based amperometric assay for the rapid quantification of extended-spectrum β-lactamase-producing Escherichia coli in wastewaters

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 electrochemical detection of Mycobacterium tuberculosis in sputum by measuring Ag85 activity with disposable carbon sensors

An electrochemical assay for the detection of the enzymatic activity of the antigen 85 (Ag85) tuberculosis (TB) biomarker was developed and evaluated for the qualitative detection of Mycobacterium tuberculosis in decontaminated sputum. For this purpose, the electroactive properties of both synthetic p-aminophenyl-6-O-octanoyl-3-d-glucopyranoside (p-APOG) substrate and p-aminophenyl-6-3-d-glucopyranoside (p-APG) product released after the removal of the octanoyl fatty acid by the Ag85 were investigated with disposable carbon screen-printed electrodes by cyclic voltammetry. Since specific anodic responses were obtained for the p-APOG substrate and the p-APG product, the intensity of the oxidation peak of the p-APG (E = + 0.35 V vs. Ag/AgCl) was selected as the analytical response for the detection of the Ag85 acyltransferase activity. Once the proof of concept of the Ag85 electrochemical assay was validated with a commercially-available Ag85B protein, its specificity was further assessed by analyzing pure cultures of various bacteria including tuberculous and non-tuberculous mycobacteria as well as different species found in patients' sputum. Finally, with a specificity of 78% and a sensitivity of 89%, the method was successfully compared to microscopy and culture routine tests for TB testing in 36 frozen fluidized and decontaminated sputum. This suggests that owing to its convenience, rapidity, low-cost and portability, the reported Ag85 electrochemical assay is a promising tool to screen patients for TB.

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.

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.

Rapid Detection of β-Lactamase-Producing Bacteria Using the Integrated Comprehensive Droplet Digital Detection (IC 3D) System

Antibiotic-resistant bacteria have emerged as an imminent global threat. The lack of rapid and sensitive diagnostic techniques leaves health care providers with inadequate resources for guiding therapy and risks the lives of patients. The traditional plate culturing methods for identifying antibiotic-resistant bacteria is laborious and time-consuming. Bulk PCR (Polymerase Chain Reaction) and qPCR are limited by poor detection sensitivity, which is critical for the early-stage detection of bloodstream infections. In this study, we introduce a technique for detecting β-lactamase-producing bacteria at single-cell sensitivity based on a commercial β-lactamase sensor (Fluorocillin), droplet microfluidics, and a custom 3D particle counter. Bacteria-containing samples were encapsulated within picoliter-sized droplets at the single-cell level and cultured within water-in-oil droplets containing antibiotics and the Fluorocillin sensor. Then, fluorescent droplets were digitally quantified with the 3D particle counter, which is capable of analyzing milliliter-scale volumes of collected droplets within 10 min. The fluorescence signal from single-colony droplets was detectable in less than 5 h, and the 3D scanning was performed in less than 10 min, which was significantly faster than conventional culture-based methods. In this approach, the limit of detection achieved was about 10 bacterial cells per mL of sample, and the turnaround time from sample to result was less than 6 h. This study demonstrates a promising strategy for the detection of β-lactamase-producing bacteria using the recently developed IC 3D system.

The coupling of immunomagnetic enrichment of bacteria with paper-based platform

In this study, the coupling of magnetic enrichment of bacteria from real samples with rapid surface enhanced Raman spectroscopy (SERS) detection was reported. The selective isolation and enrichment for the model bacteria Escherichia coli (E. coli) was performed using E. coli (primary) antibody bound-magnetic gold (Fe₃O₄@Au) nanoparticles. Following isolation and enrichment, the rennet enzyme was used to cleave of casein modified Fe₃O₄/Au-PEI nanoparticles from primary antibody-bound bacteria to prevent the nanoparticle aggregation and provide the movement of bacteria on nitrocellulose membrane. In the first part of the study, optimization studies were carried out namely; the amounts of gold nanoparticles (AuNPs), polyethyleneimine coated magnetic gold (Fe₃O₄/Au-PEI) nanoparticles, casein and rennet enzyme. The SERS signals of DTNB (5,5'-Dithiobis(2-nitrobenzoic acid)) molecule were collected on the test line and a calibration curve was plotted by using signal intensities. The correlation between the concentration of E. coli and SERS signal was found to be linear within the range of 10¹-10⁷ cfu/mL (R² = 0.984, LOD = 0.52 cfu/mL and LOQ = 1.57 cfu/mL). The selectivity of the paper-based lateral flow immunoassay (LFIA) was examined with Bacillus subtilis (B. subtilis), Micrococcus luteus (M. luteus), Salmonella enteritidis (S. enteritidis) which did not produce any significant response compared with E. coli measurement. Finally, the developed paper-based LFIA was tested with urine and milk samples. The obtained SERS results were compared with a plate counting method results which were in a good accordance. The developed method was found as rapid and sensitive to E. coli with a total analysis time of less than 60 min.