A Microtiter Plate Assay at Acidic pH to Identify Potentiators that Enhance Pyrazinamide Activity Against Mycobacterium tuberculosis.

Pyrazinamide (PZA) is a key component of chemotherapy for the treatment of drug-susceptible tuberculosis (TB) and is likely to continue to be included in new drug combinations. Potentiation of PZA could be used to reduce the emergence of resistance, shorten treatment times, and lead to a reduction in the quantity of PZA consumed by patients, thereby reducing the toxic effects. Acidified medium is required for the activity of PZA against Mycobacterium tuberculosis. In vitro assessments of pyrazinamide activity are often avoided because of the lack of standardization, which has led to a lack of effective in vitro tools for assessing and/or enhancing PZA activity.We have developed and optimized a novel, robust, and reproducible, microtiter plate assay, that centers around acidity levels that are low enough for PZA activity. The assay can be applied to the evaluation of novel compounds for the identification of potentiators that enhance PZA activity. In this assay, potentiation of PZA is demonstrated to be statistically significant with the addition of rifampicin (RIF), which can, therefore, be used as a positive control. Conversely, norfloxacin demonstrates no potentiating activity with PZA and can be used as a negative control. The method, and the associated considerations, described here, can be adapted in the search for potentiators of other antimicrobials.

A combination of nirmatrelvir and ombitasvir boosts inhibition of SARS-CoV-2 replication.

Antiviral therapeutics are highly effective countermeasures for the treatment of coronavirus disease 2019 (COVID-19). However, development of resistance to antivirals undermines their effectiveness. Combining multiple antivirals during patient treatment has the potential to overcome the evolutionary selective pressure towards antiviral resistance, as well as provide a more robust and efficacious treatment option. The current evidence for effective antiviral combinations to inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication is limited. Here, we demonstrate a combination of nirmatrelvir with ombitasvir, to jointly bring about potent inhibition of SARS-CoV-2 replication. We developed an in vitro 384- well plate cytopathic effect assay for the evaluation of antiviral combinations against Calu-3 cells infected with SARS-CoV-2 and found, that a combination of ombitasvir and nirmatrelvir was synergistic; thereby decreasing the nirmatrelvir IC50 by approx. 16-fold. The increased potency of the nirmatrelvir-ombitasvir combination, over nirmatrelvir alone afforded a greater than 3 log10 reduction in viral titre, which is sufficient to fully prevent the detection of progeny SARS-CoV-2 viral particles at 48 h post infection. The mechanism of this potentiated effect was shown to be, in-part, due to joint inhibition of the 3-chymotrypsin-like protease via a positive allosteric modulation mechanism.

Antibiotic-Loaded Polymersomes for Clearance of Intracellular Burkholderia thailandensis.

Melioidosis caused by the facultative intracellular pathogen Burkholderia pseudomallei is difficult to treat due to poor intracellular bioavailability of antibiotics and antibiotic resistance. In the absence of novel compounds, polymersome (PM) encapsulation may increase the efficacy of existing antibiotics and reduce antibiotic resistance by promoting targeted, infection-specific intracellular uptake. In this study, we developed PMs composed of widely available poly(ethylene oxide)-polycaprolactone block copolymers and demonstrated their delivery to intracellular B. thailandensis infection using multispectral imaging flow cytometry (IFC) and coherent anti-Stokes Raman scattering microscopy. Antibiotics were tightly sequestered in PMs and did not inhibit the growth of free-living B. thailandensis. However, on uptake of antibiotic-loaded PMs by infected macrophages, IFC demonstrated PM colocalization with intracellular B. thailandensis and a significant inhibition of their growth. We conclude that PMs are a viable approach for the targeted antibiotic treatment of persistent intracellular Burkholderia infection.