Rapid functional definition of extended spectrum β-lactamase activity in bacterial cultures via competitive inhibition of fluorescent substrate cleavage

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.

Quantitative Insights Into β-Lactamase Inhibitor's Contribution in the Treatment of Carbapenemase-Producing Organisms With β-Lactams

Objectives: Carbapenemase-producing organisms (CPOs) are associated with high mortality rates. The recent development of β-lactamase inhibitors (BLIs) has made it possible to control CPO infections safely and effectively with β-lactams (BLs). This study aims to explicate the quantitative relationship between BLI’s β-lactamase inhibition and CPO’s BL susceptibility restoration, thereby providing the infectious disease society practical scientific grounds for regulating the use of BL/BLI in CPO infection treatment.

Methods: A diverse collection of human CPO infection isolates was challenged by three structurally representative BLIs available in the clinic. The resultant β-lactamase inhibition, BL susceptibility restoration, and their correlation were followed quantitatively for each isolate by coupling FIBA (fluorescence identification of β-lactamase activity) and BL antibiotic susceptibility testing.

Results: The β-lactamase inhibition and BL susceptibility restoration are positively correlated among CPOs under the treatment of BLIs. Both of them are dependent on the target CPO’s carbapenemase molecular identity. Of note, without sufficient β-lactamase inhibition, CPO’s BL susceptibility restoration is universally low across all tested carbapenemase molecular groups. However, a high degree of β-lactamase inhibition would not necessarily lead to a substantial BL susceptibility restoration in CPO probably due to the existence of non-β-lactamase BL resistance mechanisms.

Conclusion: BL/BLI choice and dosing should be guided by quantitative tools that can evaluate the inhibition across the entire β-lactamase background of the CPO upon the BLI administion. Furthermore, rapid molecular diagnostics for BL/BLI resistances, especially those sensitive to β-lactamase independent BL resistance mechanisms, should be exploited to prevent ineffective BL/BLI treatment.

One-Step Detection and Classification of Bacterial Carbapenemases in 10 Minutes Using Fluorescence Identification of β-Lactamase Activity

Rapid and accurate diagnosis of bacterial carbapenemases remains a major challenge for clinical laboratories. A novel assay was developed here using fluorescence identification of β-lactamase activity (FIBA) to permit rapid detection and classification of bacterial carbapenemases. By mixing a fluorogenic β-lactamase substrate, β-LEAF (β-lactamase enzyme-activated fluorophore), with bacterial isolates plus the respective inhibitor (imipenem for noncarbapenemase β-lactamases, clavulanic acid for type A carbapenemases, and EDTA for type B carbapenemases), objective results with 95% to 100% sensitivity and specificity were generated in 10 min. FIBA is ≈$1/test and consists of only a single mixing step. Given the combination of rapidity, accuracy, low cost, and simplicity, this novel carbapenemase detection and classification assay is well positioned to be applied in clinical microbiology laboratories to provide guidance for the choice of proper treatment and control of globally prevalent carbapenemase-positive infections.

Novel Rapid Test for Detecting Carbapenemase

We developed a carbapenemase test based on the ability of imipenem to inhibit noncarbapenemase β-lactamases. The test uses bacterial isolates with a fluorescent β-lactamase substrate, producing objective results with 100% sensitivity and specificity in 10 minutes. The assay is inexpensive and consists of only 1 mixing step.

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization - a Thomas Dougherty Award for Excellence in PDT paper

Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemical, photosensitizer, which preferentially accumulates in tissues/cells and, upon irradiation with the appropriate wavelength of light, confers cytotoxicity by generation of reactive molecular species. The preferential accumulation however is not universal and, depending on the anatomical site, the ratio of tumor to normal tissue may be reversed in favor of normal tissue. Under such circumstances, control of the volume of light illumination provides a second handle of selectivity. Singlet oxygen is the putative favorite reactive molecular species although other entities such as nitric oxide have been credibly implicated. Typically, most photosensitizers in current clinical use have a finite quantum yield of fluorescence which is exploited for surgery guidance and can also be incorporated for monitoring and treatment design. In addition, the photodynamic process alters the cellular, stromal, and/or vascular microenvironment transiently in a process termed photodynamic priming, making it more receptive to subsequent additional therapies including chemo- and immunotherapy. Thus, photodynamic priming may be considered as an enabling technology for the more commonly used frontline treatments. Recently, there has been an increase in the exploitation of the theranostic potential of photodynamic therapy in different preclinical and clinical settings with the use of new photosensitizer formulations and combinatorial therapeutic options. The emergence of nanomedicine has further added to the repertoire of photodynamic therapy's potential and the convergence and co-evolution of these two exciting tools is expected to push the barriers of smart therapies, where such optical approaches might have a special niche. This review provides a perspective on current status of photodynamic therapy in anti-cancer and anti-microbial therapies and it suggests how evolving technologies combined with photochemically-initiated molecular processes may be exploited to become co-conspirators in optimization of treatment outcomes. We also project, at least for the short term, the direction that this modality may be taking in the near future.

Guiding Empiric Treatment for Serious Bacterial Infections via Point of Care [Formula: see text]-Lactamase Characterization

Fever is one of the most common symptoms of illness in infants and represents a clinical challenge due to the potential for serious bacterial infection. As delayed treatment for these infections has been correlated with increased morbidity and mortality, broad-spectrum [Formula: see text]-lactam antibiotics are often prescribed while waiting for microbiological lab results (1-3 days). However, the spread of antibiotic resistance via the [Formula: see text]-lactamase enzyme, which can destroy [Formula: see text]-lactam antibiotics, has confounded this paradigm; empiric antibiotic regimens are increasingly unable to cover all potential bacterial pathogens, leaving some infants effectively untreated until the pathogen is characterized. This can lead to lifelong sequela or death. Here, we introduce a fluorescent, microfluidic assay that can characterize [Formula: see text]-lactamase derived antibiotic susceptibility in 20 min with a sensitivity suitable for direct human specimens. The protocol is extensible, and the antibiotic spectrum investigated can be feasibly adapted for the pathogens of regional relevance. This new assay fills an important need by providing the clinician with hitherto unavailable point of care information for treatment guidance in an inexpensive and simple diagnostic format.

Rapid optical determination of β-lactamase and antibiotic activity

BACKGROUND

The absence of rapid tests evaluating antibiotic susceptibility results in the empirical prescription of antibiotics. This can lead to treatment failures due to escalating antibiotic resistance, and also furthers the emergence of drug-resistant bacteria. This study reports a rapid optical method to detect β-lactamase and thereby assess activity of β-lactam antibiotics, which could provide an approach for targeted prescription of antibiotics. The methodology is centred on a fluorescence quenching based probe (β-LEAF--β-Lactamase Enzyme Activated Fluorophore) that mimics the structure of β-lactam antibiotics.

RESULTS

The β-LEAF assay was performed for rapid determination of β-lactamase production and activity of β-lactam antibiotic (cefazolin) on a panel of Staphylococcus aureus ATCC strains and clinical isolates. Four of the clinical isolates were determined to be lactamase producers, with the capacity to inactivate cefazolin, out of the twenty-five isolates tested. These results were compared against gold standard methods, nitrocefin disk test for β-lactamase detection and disk diffusion for antibiotic susceptibility, showing results to be largely consistent. Furthermore, in the sub-set of β-lactamase producers, it was demonstrated and validated that multiple antibiotics (cefazolin, cefoxitin, cefepime) could be assessed simultaneously to predict the antibiotic that would be most active for a given bacterial isolate.

CONCLUSIONS

The study establishes the rapid β-LEAF assay for β-lactamase detection and prediction of antibiotic activity using S. aureus clinical isolates. Although the focus in the current study is β-lactamase-based resistance, the overall approach represents a broad diagnostic platform. In the long-term, these studies form the basis for the development of assays utilizing a broader variety of targets, pathogens and drugs.