Early diagnosis of tuberculosis can dramatically reduce both its transmission and the associated death rate. The extremely slow growth rate of the causative pathogen, Mycobacterium tuberculosis (Mtb), however, makes this challenging at the point of care, particularly in resource-limited settings. Here we report the use of BlaC (an enzyme naturally expressed/secreted by tubercle bacilli) as a marker and the design of BlaC-specific fluorogenic substrates as probes for Mtb detection. These probes showed an enhancement by 100–200 times in fluorescence emission on BlaC activation and a greater than 1,000-fold selectivity for BlaC over TEM-1 β-lactamase, an important factor in reducing false-positive diagnoses. Insight into the BlaC specificity was revealed by successful co-crystallization of the probe/enzyme mutant complex. A refined green fluorescent probe (CDG-OMe) enabled the successful detection of live pathogen in less than ten minutes, even in unprocessed human sputum. This system offers the opportunity for the rapid, accurate detection of very low numbers of Mtb for the clinical diagnosis of tuberculosis in sputum and other specimens.
Current methods for the detection of Mycobacterium tuberculosis (Mtb) are either time consuming or require expensive instruments and are thus are not suitable for point-of-care diagnosis. The design, synthesis, and evaluation of fluorogenic probes with high specificity for BlaC, a biomarker expressed by Mtb, are described. The fluorogenic probe CDG-3 is based on cephalosporin with substitutions at the 2 and 7 positions and it demonstrates over 120 000-fold selectivity for BlaC over TEM-1 Bla, the most common β-lactamase. CDG-3 can detect 10 colony-forming units of the attenuated Mycobacterium bovis strain BCG in human sputum in the presence of high levels of contaminating β-lactamases expressed by other clinically prevalent bacterial strains. In a trial with 50 clinical samples, CDG-3 detected tuberculosis with 90 % sensitivity and 73 % specificity relative to Mtb culture within one hour, thus demonstrating its potential as a low-cost point-of-care test for use in resource-limited areas.
Slow growth of
Mycobacterium tuberculosis
(Mtb), the causative agent of tuberculosis (TB), hinders advancement in all areas of research toward prevention and treatment. Real time imaging, employing reporter enzyme fluorescence (REF) that uses custom fluorogenic substrates for bacterial enzymes, allows rapid and specific detection of Mtb in live animals. We have synthesized a novel REF substrate, CNIR800, which carries a near-infrared (NIR) fluorochrome IRDye 800CW, with a quencher connected through the lactam ring that is hydrolyzed by the enzyme BlaC (β-lactamase) naturally expressed by Mtb. CNIR800 produces long wavelength emission at 795 nm upon excitation (745 nm) and exhibits significantly improved signal-to-noise ratios for detection of Mtb
.
The detection threshold with CNIR800 is ∼100 colony forming units (CFU)
in vitro
and <1000 CFU in the lungs of mice. Additionally, fluorescence signal from cleaved CNIR800 reaches maximal levels at 4-6 h post-administration in live animals, allowing accurate evaluation of anti-tuberculous drug efficacy. Thus, CNIR800 represents an excellent substrate for accurate detection of Mtb rapidly and specifically in animals, facilitating research toward understanding pathogenic mechanisms, evaluation of therapeutic outcomes, and screening new vaccines.
Tuberculosis is the most frequent cause of death in humans from a single infectious agent. Due to low numbers of bacteria present in sputum during early infection, diagnosis does not usually occur until >3 to 4 months after symptoms develop. We created a new more sensitive diagnostic that can be carried out in 10 min with no processing or technical expertise.
Current methods for the detection of Mycobacterium tuberculosis (Mtb) are either time consuming or require expensive instruments and are thus are not suitable for pointof-care diagnosis. The design, synthesis, and evaluation of fluorogenic probes with high specificity for BlaC, a biomarker expressed by Mtb, are described. The fluorogenic probe CDG-3 is based on cephalosporin with substitutions at the 2 and 7 positions and it demonstrates over 120 000-fold selectivity for BlaC over TEM-1 Bla, the most common b-lactamase. CDG-3 can detect 10 colony-forming units of the attenuated Mycobacterium bovis strain BCG in human sputum in the presence of high levels of contaminating b-lactamases expressed by other clinically prevalent bacterial strains. In a trial with 50 clinical samples, CDG-3 detected tuberculosis with 90 % sensitivity and 73 % specificity relative to Mtb culture within one hour, thus demonstrating its potential as a low-cost pointof-care test for use in resource-limited areas.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.