Killer applications: Toward affordable rapid cell-based diagnostics for malaria and tuberculosis

Extreme Drug Tolerance of Mycobacterium tuberculosis in Caseum

Tuberculosis (TB) recently became the leading infectious cause of death in adults, while attempts to shorten therapy have largely failed. Dormancy, persistence, and drug tolerance are among the factors driving the long therapy duration. Assays to measure in situ drug susceptibility of Mycobacterium tuberculosis bacteria in pulmonary lesions are needed if we are to discover new fast-acting regimens and address the global TB threat. Here we take a first step toward this goal and describe an ex vivo assay developed to measure the cidal activity of anti-TB drugs against M. tuberculosis bacilli present in cavity caseum obtained from rabbits with active TB. We show that caseum M. tuberculosis bacilli are largely nonreplicating, maintain viability over the course of the assay, and exhibit extreme tolerance to many first- and second-line TB drugs. Among the drugs tested, only the rifamycins fully sterilized caseum. A similar trend of phenotypic drug resistance was observed in the hypoxia- and starvation-induced nonreplicating models, but with notable qualitative and quantitative differences: (i) caseum M. tuberculosis exhibits higher drug tolerance than nonreplicating M. tuberculosis in the Wayne and Loebel models, and (ii) pyrazinamide is cidal in caseum but has no detectable activity in these classic nonreplicating assays. Thus, ex vivo caseum constitutes a unique tool to evaluate drug potency against slowly replicating or nonreplicating bacilli in their native caseous environment. Intracaseum cidal concentrations can now be related to the concentrations achieved in the necrotic foci of granulomas and cavities to establish correlations between clinical outcome and lesion-centered pharmacokinetics-pharmacodynamics (PK-PD) parameters.

Dual-label flow cytometry-based host cell adhesion assay to ascertain the prospect of probiotic Lactobacillus plantarum in niche-specific antibacterial therapy

Host cell adhesion assays that provide quantitative insight on the potential of lactic acid bacteria (LAB) to inhibit adhesion of intestinal pathogens can be leveraged for the development of niche-specific anti-adhesion therapy. Herein, we report a dual-colour flow cytometry (FCM) analysis to assess the ability of probiotic Lactobacillus plantarum strains to impede adhesion of Enterococcus faecalis, Listeria monocytogenes and Staphylococcus aureus onto HT-29 cells. FCM in conjunction with a hierarchical cluster analysis could discern the anti-adhesion potential of L. plantarum strains, wherein the efficacy of L. plantarum DF9 was on a par with the probiotic L. rhamnosus GG. Combination of FCM with principal component analysis illustrated the relative influence of LAB strains on adhesion parameters kd and em of the pathogen and identified probiotic LAB suitable for anti-adhesion intervention. The analytical merit of the FCM analysis was captured in host cell adhesion assays that measured relative elimination of adhered LAB vis-à-vis pathogens, on exposure to either LAB bacteriocins or therapeutic antibiotics. It is envisaged that the dual-colour FCM-based adhesion assay described herein would enable a fundamental understanding of the host cell adhesion process and stimulate interest in probiotic LAB as safe anti-adhesion therapeutic agents against gastrointestinal pathogens.

The development, evaluation and performance of molecular diagnostics for detection of Mycobacterium tuberculosis

The unique pathogenesis of tuberculosis (TB) poses several barriers to the development of accurate diagnostics: a) the establishment of life-long latency by Mycobacterium tuberculosis (M.tb) after primary infection confounds the development of classical antibody or antigen based assays; b) our poor understanding of the molecular pathways that influence progression from latent to active disease; c) the intracellular nature of M.tb infection in tissues means that M.tb and/or its components, are not readily detectable in peripheral specimens; and d) the variable presence of M.tb bacilli in specimens from patients with extrapulmonary TB or children. The literature on the current portfolio of molecular diagnostics tests for TB is reviewed here and the developmental pipeline is summarized. Also reviewed are data from recently published operational research on the GeneXpert MTB/RIF assay and discussed are the lessons that can be taken forward for the design of studies to evaluate the impact of TB diagnostics.

Light-emitting diode fluorescence microscopy for tuberculosis diagnosis: a meta-analysis

Light-emitting diode fluorescence microscopy (LED-FM) is recommended by the World Health Organization to replace conventional Ziehl-Neelsen microscopy for pulmonary tuberculosis diagnosis. Uptake of LED-FM has been slow. One reason is its reported loss of specificity compared with Ziehl-Neelsen microscopy. We aimed to determine the diagnostic accuracy of LED-FM for tuberculosis detection and explore potential factors that might affect its performance.A comprehensive search strategy based on pre-specified criteria was employed to identify eligible studies between January 1, 2000 and April 1, 2014 in 11 databases. Standardised study selection, data extraction and quality assessment were conducted. Pooled sensitivity and specificity of LED-FM using culture as the reference standard were estimated through meta-analyses using a bivariate random-effects model. Investigation of heterogeneity was performed by subgroup analyses.We identified 12 unique studies, half of which were from peripheral healthcare facilities. LED-FM achieved a pooled sensitivity of 66.9% (95% CI 60.5-72.7%) and pooled specificity of 96.8% (95% CI 93.1-98.6%). A pooled sensitivity of 53.0% (95% CI 42.8-63.0%) and pooled specificity of 96.1% (95% CI 86.0-99.0%) were obtained by LED-FM among HIV-infected patients. Study methodology factors and differences in the LED-FM procedure or device could also affect the performance.LED-FM specificity is high and should not be a barrier to device introduction, particularly among peripheral healthcare settings where this technology is meant to be used. Sensitivity is reduced in HIV-infected patients.

Rifabutin reduces systemic exposure of an antimalarial drug 97/78 upon co-administration in rats: An in-vivo &in-vitro analysis

OBJECTIVE

To determine the potential drug-drug interactions between anti-malarial candidate 97/78 and anti-tubercular drug rifabutin in-vivo in rats followed by in-vitro investigation of the underlying mechanisms of drug interaction.

METHODS

Single oral dose study was conducted in male and female rats at 40 mg/kg and 70 mg/kg for 97/78 and rifabutin respectively.

RESULTS

It was reported that rifabutin co-administration altered pharmacokinetics of 97/63 (active metabolite of 97/78). A significant decrease was reported in the systemic exposure of 97/63 by a factor of 3-4. The AUC0-last values were (4.03 ± 0.60) and (5.44 ± 1.15) μg h mL(-1) upon 97/78 administration alone, while the values were decreased to (1.13 ± 0.10) and (1.23 ± 1.13) μg h mL(-1) upon rifabutin co-administration in male and female rats respectively. Statistically significant differences were also reported in Cmax and Tmax values upon rifabutin co-administration. In-vitro drug metabolism study in rat liver microsomes has shown that the metabolism of 97/63 was increased by 10%-12% upon rifabutin co-incubation. The extent of plasma protein binding of 97/63 was found to be decreased from 54%-55% to 6%-8% upon rifabutin addition.

CONCLUSIONS

It was concluded that rifabutin co-administration altered PK parameters of 97/63 in SD rats. However, no intersex influences were reported in the interaction pattern. The results obtained in the in-vivo study were well correlated with the in-vitro findings and can further be applied to explore other aspects of potential drug interactions between these two drugs.

One nanoprobe, two pathogens: gold nanoprobes multiplexing for point-of-care

Background

Gold nanoparticles have been widely employed for biosensing purposes with remarkable efficacy for DNA detection. Amongst the proposed systems, colorimetric strategies based on the remarkable optical properties have provided for simple yet effective sequence discrimination with potential for molecular diagnostics at point of need. These systems may also been used for parallel detection of several targets to provide additional information on diagnostics of pathogens.

Results

For the first time, we demonstrate that a single Au-nanoprobe may provide for detection of two distinct targets (pathogens) allowing colorimetric multi-target detection. We demonstrate this concept by using one single gold-nanoprobe capable to detect members of the Mycobacterium tuberculosis complex and Plasmodium sp., the etiologic agents of tuberculosis and malaria, respectively. Following characterisation, the developed gold-nanoprobe allowed detection of either target in individual samples or in samples containing both DNA species with the same efficacy.

Conclusions

Using one single probe via the non-cross-linking colorimetric methodology it is possible to identify multiple targets in one sample in one reaction. This proof-of-concept approach may easily be integrated into sensing platforms allowing for fast and simple multiplexing of Au-nanoprobe based detection at point-of-need.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-015-0109-1) contains supplementary material, which is available to authorized users.

High-throughput multi-parameter flow-cytometric analysis from micro-quantities of plasmodium-infected blood

Despite significant technological and conceptual advances over the last century, evaluation of the efficacy of anti-malarial vaccines or drugs continues to rely principally on direct microscopic visualisation of parasites on thick and/or thin Giemsa-stained blood smears. This requires technical expertise of the microscopist, is highly subjective and error-prone, and does not account for aberrations such as anaemia. Many published methods have shown that flow cytometric analysis of blood is a highly versatile method that can readily detect nucleic acid-stained parasitised red blood cells within cultured cell populations and in ex-vivo samples. However several impediments, including the difficulty in distinguishing reticulocytes from infected red blood cells and the fickle nature of red blood cells, have precluded the development and universal adoption of flow-cytometric based assays for ex-vivo sample analysis. We have developed a novel high-throughput assay for the flow cytometric assessment of blood that overcomes these impediments by utilising the unique properties of the nucleic acid stain DAPI to differentially stain RNA and DNA, combined with novel fixation and analysis protocols. The assay allows the rapid and reliable analysis of multiple parameters from micro-volumes of blood, including: parasitaemia, platelet count, reticulocyte count, normocyte count, white blood cell count and delineation of subsets and phenotypic markers including, but not limited to, CD4(+) and CD8(+) T cells, and the expression of phenotypic markers such as PD-L1 or intracellular cytokines. The assay requires less than one drop of blood and is therefore suitable for short interval time-course experiments and allows the progression of infection and immune responses to be closely monitored in the laboratory or cytometer-equipped field locations. Herein, we describe the technique and demonstrate its application in vaccinology and with a range of rodent and human parasite species including Plasmodium yoelii, Plasmodium chabaudi, Plasmodium berghei and Plasmodium falciparum.

Methodology and application of flow cytometry for investigation of human malaria parasites

Historically, examinations of the inhibition of malaria parasite growth/invasion, whether using drugs or antibodies, have relied on the use of microscopy or radioactive hypoxanthine uptake. These are considered gold standards for measuring the effectiveness of antimalarial treatments, however, these methods have well known shortcomings. With the advent of flow cytometry coupled with the use of fluorescent DNA stains allowed for increased speed, reproducibility, and qualitative estimates of the effectiveness of antibodies and drugs to limit malaria parasite growth which addresses the challenges of traditional techniques. Because materials and machines available to research facilities are so varied, different methods have been developed to investigate malaria parasites by flow cytometry. This review is intended to serve as a reference guide for advanced users and importantly, as a primer for new users, to support expanded use and improvements to malaria flow cytometry, particularly in endemic countries.

A research agenda for malaria eradication: diagnoses and diagnostics

Many of malaria's signs and symptoms are indistinguishable from those of other febrile diseases. Detection of the presence of Plasmodium parasites is essential, therefore, to guide case management. Improved diagnostic tools are required to enable targeted treatment of infected individuals. In addition, field-ready diagnostic tools for mass screening and surveillance that can detect asymptomatic infections of very low parasite densities are needed to monitor transmission reduction and ensure elimination. Antibody-based tests for infection and novel methods based on biomarkers need further development and validation, as do methods for the detection and treatment of Plasmodium vivax. Current rapid diagnostic tests targeting P. vivax are generally less effective than those targeting Plasmodium falciparum. Moreover, because current drugs for radical cure may cause serious side effects in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, more information is needed on the distribution of G6PD-deficiency variants as well as tests to identify at-risk individuals. Finally, in an environment of very low or absent malaria transmission, sustaining interest in elimination and maintaining resources will become increasingly important. Thus, research is required into the context in which malaria diagnostic tests are used, into diagnostics for other febrile diseases, and into the integration of these tests into health systems.

The cytometric future: it ain't necessarily flow!

Initial approaches to cytometry for classifying and characterizing cells were based on microscopy; it was necessary to collect relatively high-resolution images of cells because only a few specific reagents usable for cell identification were available. Although flow cytometry, now the dominant cytometric technology, typically utilizes lenses similar to microscope lenses for light collection, improved, more quantitative reagents allow the necessary information to be acquired in the form of whole-cell measurements of the intensities of light transmission, scattering, and/or fluorescence.Much of the cost and complexity of both automated microscopes and flow cytometers arises from the necessity for them to measure one cell at a time. Recent developments in digital camera technology now offer an alternative in which one or more low-magnification, low-resolution images are made of a wide field containing many cells, using inexpensive light-emitting diodes (LEDs) for illumination. Minimalist widefield imaging cytometers can provide a smaller, less complex, and substantially less expensive alternative to flow cytometry, critical in systems intended for in resource-poor areas. Minimalism is, likewise, a good philosophy in developing instrumentation and methodology for both clinical and large-scale research use; it simplifies quality assurance and compliance with regulatory requirements, as well as reduces capital outlays, material costs, and personnel training requirements. Also, importantly, it yields "greener" technology.

Is flow cytometry better in counting malaria pigment-containing leukocytes compared to microscopy?

Background

Detection of malaria pigment (or haemozoin; Hz)-containing leukocytes may have prognostic relevance in malaria; however, studies reported conflicting results, with microscopic counts suggestive of being inaccurate and imprecise.

Methods

Numbers of Hz-containing leukocytes from a malaria patient obtained with a flow cytometer counting 50.000 gated events were compared with thin film microscopy as applied under field conditions.

Results

Flow cytometry identified 5.8% Hz-containing monocytes and 1.8% Hz-containing neutrophils. The microscopic examination yielded 10% and 13% of Hz-containing monocytes, as well as 0% and 0.5% of Hz-containing neutrophils for observers one and two, respectively.

Conclusion

Novel, robust and affordable cytometric methods should be evaluated in the field as they may assist in utilizing Hz-containing cells as clinically useful parameter.

Fuchsin fluorescence in Mycobacterium tuberculosis: the Ziehl-Neelsen stain in a new light

Tuberculosis (TB) is often diagnosed by observation of reddish pink fuchsin-stained Mycobacterium tuberculosis (MTB) in Ziehl-Neelsen (Z-N) stained smears by transmitted light microscopy. MTB too faintly stained with fuchsin to be seen by transmitted light may be detected by their green-excited orange-red fluorescence; this finding may be clinically relevant.

The future looks bright: low-cost fluorescent microscopes for detection of Mycobacterium tuberculosis and Coccidiae

In many resource-poor countries, diagnosis of tuberculosis is based on microscopy of Ziehl-Neelsen-stained smears. However, the fluorescent stain auramine performs better and allows the detection of more positive smears. The limitation for its widespread use has been the high cost for fluorescent microscopes, especially the frequent replacement of the expensive light source, which lasts only 200-300 h. Novel light-emitting diodes (LED) are alternatives and last ten thousands of hours. Based on LEDs, rather inexpensive solutions for fluorescent microscopes are now available and thus auramine may be a cost-effective step to improve the diagnosis of tuberculosis in resource-poor countries.