Development and validation of a rapid multiplex PCR assay for simultaneous detection of common bacterial pathogens and resistance genes in bloodstream infections

Project Abstract

This study reports the development and validation of a rapid multiplex polymerase chain reaction (PCR) assay designed to simultaneously detect common bacterial pathogens implicated in bloodstream infections (BSIs) and key antimicrobial resistance (AMR) genes, enabling timely, targeted therapeutic decisions and improved patient outcomes. The assay was engineered to identify a panel comprising Gram-positive and Gram-negative bacteria frequently recovered from BSI specimens, including Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus spp., Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella spp., alongside clinically relevant resistance determinants such as mecA, blaKPC, blaCTX-M, blaNDM, blaVIM, blaOXA-48-like, vanA/vanB, and mcr-1. Primer and probe sets were meticulously designed to minimize cross-reactivity and to optimize amplification efficiency in a single-told reaction, with an internal amplification control to monitor extraction efficiency and PCR inhibition. The assay workflow integrates rapid nucleic acid extraction from whole blood or positive blood culture bottles, followed by multiplex real-time PCR and data interpretation using a predefined threshold algorithm to yield a qualitative pathogen-identification plus resistance-gene profile within 2–3 hours. Analytical performance was established through the determination of limit of detection (LOD) for each target in simulated and clinical matrices, inclusivity testing across diverse reference strains, and exclusivity testing against phylogenetically related non-target organisms. Sensitivity and specificity were assessed using a prospective cohort of 500 archived and fresh bloodstream specimens, with conventional culture and standard phenotypic antimicrobial susceptibility testing serving as the reference standard. The multiplex assay demonstrated high analytical sensitivity with LODs ranging from 10^1 to 10^3 CFU/mL depending on the organism, and robust specificity with no cross-reactivity to non-target species. In the clinical evaluation, the assay achieved concordance with reference methods in the majority of cases, enabling earlier reporting of pathogen identity and resistance determinants compared with culture-based workflows. Importantly, the assay detected critical resistance genes that informed immediate empiric therapy adjustment and infection-control measures, including identification of methicillin-resistant Staphylococcus aureus (via mecA) and carbapenemase producers (via blaKPC, blaNDM, blaVIM, blaOXA-48-like). Discrepant results were further analyzed, revealing possible mixed infections or low bacterial loads near the detection threshold, underscoring the need for complementary culture in certain scenarios. The study also evaluated workflow feasibility in routine clinical settings, including hands-on time, turnaround time, and cost implications, and conducted a user-acceptance assessment with microbiology staff. The findings establish the multiplex assay as a reliable, rapid, and economical adjunct to conventional culture, enhancing early etiologic attribution and resistance profiling in BSIs. Limitations include the finite target panel and potential for false negatives in very low-copy-number infections or rare pathogens not encompassed by the assay. Future work will expand the panel to cover additional resistance mechanisms and incorporate semi-quantitative outputs to gauge bacterial load, with multi-center validation to ensure generalizability.

Project Overview

What This Project Is About

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The project explores a faster lab test that can detect common bacteria from blood samples at the same time as checking for genes that make them resistant to drugs. It uses a multiplex PCR method, which means multiple targets are tested in one run. The goal is to see if this approach can provide quick and reliable results to guide treatment for bloodstream infections.

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The Problem It Addresses

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Objectives of the Project

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1. Assess whether a multiplex PCR test can detect key bacterial pathogens found in bloodstream infections.
2. Determine if resistance genes to major antibiotics can be identified in the same assay.
3. Compare the new test against standard culture-based methods for accuracy and speed.
4. Evaluate the practicality of the test in a typical clinical laboratory workflow.
5. Identify any limitations and propose improvements for real-world use.

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What You Will Do Step by Step

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1. Review literature on blood culture testing and resistance detection.
2. Design a multiplex PCR panel targeting common pathogens and resistance genes.
3. Obtain and process simulated or archived blood samples for testing.
4. Run the multiplex PCR assays and record results.
5. Validate results by comparing with standard culture methods and known controls.
6. Analyze data for sensitivity, specificity, and turnaround time.
7. Discuss practical considerations for lab implementation.

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Expected Outcome