A Multi-armed Approach for Identifying Circulating Bacterial Proteins in Melioidosis

The detection of pathogen-associated macromolecules in clinical samples is a powerful alternative to more traditional gold standards of diagnosing infectious diseases. Burkholderia pseudomallei, the causative agents of melioidosis, is a facultative, intracellular bacteria categorized as a Tier 1 Select Agent by the United States Federal Government for its capacity for large-scale dissemination, elevated rates of mortality and morbidity, and minimal medical countermeasures in place. B. pseudomallei is prevalent in tropical regions and is intrinsically resistant to many first-line antibiotics. The current gold standard for diagnosing melioidosis is blood culture, however this method is inadequate and timely. The multifaceted display of clinical presentations of melioidosis further emphasize the need for specific, yet rapid diagnostics. To further characterize viable bacterial targets present during an infection, a multi-armed approach was used to analyze clinical melioidosis samples through direct and indirect platforms. First, the In vivo Microbial Antigen Discovery (InMAD) platform utilized syngeneic CD1 mice to indirectly detected bacterial proteins in clinical samples in conjunction with a high-density nucleic acid protein array (HD-NAPPA). Secondly, patient serology was evaluated on the HD-NAPPA to determine generated antibody response in the host as these proteins may be shed targets from these intracellular pathogens. Third, protein profiling by liquid chromatography with tandem mass spectrometry (LC-MS/MS) would depict proteins in an unbiased proteomic methodology. Converging data from each approach resulted in multiple targets of interest to be evaluated as biomarkers of melioidosis.

Development of a dual antigen lateral flow immunoassay for detecting Yersinia pestis

Background

Yersinia pestis is the causative agent of plague, a zoonosis associated with small mammals. Plague is a severe disease, especially in the pneumonic and septicemic forms, where fatality rates approach 100% if left untreated. The bacterium is primarily transmitted via flea bite or through direct contact with an infected host. The 2017 plague outbreak in Madagascar resulted in more than 2,400 cases and was highlighted by an increased number of pneumonic infections. Standard diagnostics for plague include laboratory-based assays such as bacterial culture and serology, which are inadequate for administering immediate patient care for pneumonic and septicemic plague.

Principal findings

The goal of this study was to develop a sensitive rapid plague prototype that can detect all virulent strains of Y. pestis. Monoclonal antibodies (mAbs) were produced against two Y. pestis antigens, low-calcium response V (LcrV) and capsular fraction-1 (F1), and prototype lateral flow immunoassays (LFI) and enzyme-linked immunosorbent assays (ELISA) were constructed. The LFIs developed for the detection of LcrV and F1 had limits of detection (LOD) of roughly 1–2 ng/mL in surrogate clinical samples (antigens spiked into normal human sera). The optimized antigen-capture ELISAs produced LODs of 74 pg/mL for LcrV and 61 pg/mL for F1 when these antigens were spiked into buffer. A dual antigen LFI prototype comprised of two test lines was evaluated for the detection of both antigens in Y. pestis lysates. The dual format was also evaluated for specificity using a small panel of clinical near-neighbors and other Tier 1 bacterial Select Agents.

Conclusions

LcrV is expressed by all virulent Y. pestis strains, but homologs produced by other Yersinia species can confound assay specificity. F1 is specific to Y. pestis but is not expressed by all virulent strains. Utilizing highly reactive mAbs, a dual-antigen detection (multiplexed) LFI was developed to capitalize on the diagnostic strengths of each target.