Recombinase polymerase amplification-lateral flow (RPA-LF) assay combined with immunomagnetic separation for rapid visual detection of Vibrio parahaemolyticus in raw oysters

This study was the first attempt to optimize a recombinase polymerase amplification (RPA) and lateral flow (LF) assay combined with immunomagnetic separation (IMS) for the detection of Vibrio parahaemolyticus in raw oysters. The newly developed IMS-RPA-LF assay effectively combines sample preparation, amplification, and detection into a single platform. Under optimal conditions, the average capture efficiency (CE) for 10⁴ colony forming units (CFU)/mL of four V. parahaemolyticus strains with 0.4 mg of immunomagnetic beads within 45 min was 80.3%. After optimization, the RPA-LF assay was able to detect V. parahaemolyticus within 15 min, comprising DNA amplification with RPA for 10 min at 37 °C and visualization of the amplicons through LF strips for 5 min. The RPA-LF assay exhibited good specificity by showing a test line for eight V. parahaemolyticus strains with different serotypes but no cross-reaction with 12 non-V. parahaemolyticus bacteria. RPA-LF assay was found to be sensitive and detected as low as 10 pg genomic DNA of V. parahaemolyticus. For spiked oyster samples, the detection sensitivity of V. parahaemolyticus was improved to 2 CFU/g by IMS-RPA-LF after enrichment for 4 h; in contrast, the IMS-PCR method required 8 h. Hence, even when V. parahaemolyticus was present in very low numbers in samples, the IMS-RPA-LF assay could be completed within half a workday. Because of the high sensitivity, specificity, and speed of the IMS-RPA-LF assay, this newly developed method opens a novel pathway for rapid diagnostic screening of V. parahaemolyticus in seafood, which is an increasingly important health issue worldwide. Graphical abstract.

Application of new host biomarker profiles in quantitative point-of-care tests facilitates leprosy diagnosis in the field

BACKGROUND

Transmission of Mycobacterium leprae, the pathogen causing leprosy, is still persistent. To facilitate timely (prophylactic) treatment and reduce transmission it is vital to both early diagnose leprosy, and identify infected individuals lacking clinical symptoms. However, leprosy-specific biomarkers are limited, particularly for paucibacillary disease. Therefore, our objective was to identify new biomarkers for leprosy and assess their applicability in point-of-care (POC) tests.

METHODS

Using multiplex-bead-arrays, 60 host-proteins were measured in a cross-sectional approach in 24-h whole blood assays (WBAs) collected in Bangladesh (79 patients; 54 contacts; 51 endemic controls (EC)). Next, 17 promising biomarkers were validated in WBAs of a separate cohort (55 patients; 27 EC). Finally, in a third cohort (36 patients; 20 EC), five candidate markers detectable in plasma were assessed for application in POC tests.

FINDINGS

This study identified three new biomarkers for leprosy (ApoA1, IL-1Ra, S100A12), and confirmed five previously described biomarkers (CCL4, CRP, IL-10, IP-10, αPGL-I IgM). Overnight stimulation in WBAs provided increased specificity for leprosy and was required for IL-10, IL-1Ra and CCL4. The remaining five biomarkers were directly detectable in plasma, hence suitable for rapid POC tests. Indeed, lateral flow assays (LFAs) utilizing this five-marker profile detected both multi- and paucibacillary leprosy patients with variable immune responses.

INTERPRETATION

Application of novel host-biomarker profiles to rapid, quantitative LFAs improves leprosy diagnosis and allows POC testing in low-resource settings. This platform can thus aid diagnosis and classification of leprosy and also provides a tool to detect M.leprae infection in large-scale contact screening in the field.