Bacterial infections are a major cause of mortality and morbidity in the world, and new strategies for improving their treatment are greatly needed. A key issue limiting treatment of bacterial infections is an inability to rapidly determine antibioti susceptibilities. Conventional microbiological diagnosis depends on culturing from bodily specimens, often requiring 1-3 day incubations that can be further delayed by the presence of fastidious pathogens. The objective of this proposal is to develop a flow cytometric strategy for rapidly determining MICs of antibiotics against the six most common blood stream infections (BSI). Requiring <1-hr antibiotic incubation times to see characteristic responses, this new susceptibility strategy is designed to determine antimicrobial MICs within 4 hours of blood culture positivity, portending significant improvements to patient treatment outcomes and lowered incidence of drug resistance caused by excessive antibiotic use. The flow cytometric methods proposed here rely on statistical, scattered light and selective bacterial (vs. mammalian cell) delivery and enrichment technologies recently developed in our laboratories. The central hypothesis of this proposal is that "Antimicrobial susceptibility can be generated within 4 hours of positive blood culture, for the six most common BSI-causing bacteria, using a combination of flow cytometry technologies that measure antibiotic-induced ROS and scatter changes in bacteria, each coupled with rigorous multidimensional statistical distance metrics for quantification." The experiments in this proposal will develop a complementary set of flow cytometric technologies that rapidly detect antibacterial MICs of bacteria either grown in culture or when tagged directly within positive blood cultures. When successful, these studies will reduce the time to antibiotic sensitivity determinations to as little as ~4 hours, post positive blood culture. Removing this treatment bottleneck will enable action- able information to be garnered at least 36 hours faster than currently possible, directly impacting patient out- comes and minimizing antibiotic overuse and resistance concerns.
Each Aim utilizes highly innovative technologies to achieve these potential significant benefits to human health.
In Aim 1, our unique maltodextrin-based bacterial targeting, and our highly sensitive fluorogenic ROS dosimeters will be combined and applied to quantify the demonstrated ROS production upon near-MIC antibiotic exposure.
Aim 2 will demonstrate that <1-hr, near-MIC antibiotic exposure induces characteristic bacterial morphology changes are detectable with scattered light. Multidimensional statistical distance metrics vs. paired and unpaired controls are developed to quantify these changes and determine label-free MICs in the presence of biovariability.
Aim 3 will combine the innovations of Aims 1 &2 to probe clinical isolates using ROS and scatter with 3-D statistical distance metrics, while further decreasing time-to-result by gating on fluorophore-targeted bacteria directly within blood culture. We anticipate widespread interest in the experiments proposed here, given the great need for new bacterial diagnostics and the tremendous human and economic costs of bacterial infections.

Public Health Relevance

This proposal develops new technologies to speed antimicrobial sensitivity testing from the current ~48 hours to ~4 hours after positive blood culture using both fluorescent and label-free detection. Actionable treatment information requires both identification and antibiotic sensitivity determinations - the latter being the true bottleneck in treatment that both negatively impacts patient health and increases antibiotic resistance through empiric treatments. New flow cytometric scatter and fluorescence sensing measurements, coupled with adaptive, multidimensional statistical methods developed specifically for this purpose suggest eventual translation to the clinic to positively impact treatment and overall human health.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
High Priority, Short Term Project Award (R56)
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Enabling Bioanalytical and Imaging Technologies Study Section (EBIT)
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Ritchie, Alec
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Georgia Institute of Technology
Schools of Arts and Sciences
United States
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