New Contrast Agents Detect Bacterial İnfections With High Sensitivity and Specificity

A new family of contrast agents that sneak into bacteria disguised as glucose food can detect bacterial infections in animals with high sensitivity and specificity. These agents -- called maltodextrin-based imaging probes -- can also distinguish a bacterial infection from other inflammatory conditions. "These contrast agents fill the need for probes that can accurately image small numbers of bacteria in vivo and distinguish infections from other pathologies like cancer," said Niren Murthy, an associate professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "These probes could ultimately improve the diagnosis and treatment of bacterial infections, which remains a major challenge in medicine."

The imaging probes were described in the July 17, 2011 advance online edition of the journal Nature Materials. The research was sponsored by the National Science Foundation and National Institutes of Health.

Coulter Department postdoctoral fellows Xinghai Ning and Seungjun Lee led the project. University of Georgia Complex Carbohydrate Research Center postdoctoral associate Zhirui Wang; and Georgia State University Department of Biology associate professor Eric Gilbert and student Bryan Subblefield also contributed to the work.

In the United States in 2010, bacterial infections caused 40,000 deaths from sepsis and were the leading cause of limb amputations. A major limitation preventing the effective treatment of bacterial infections is an inability to detect them inside the body with accuracy and sensitivity. To image bacterial infections, probes must first deliver a large quantity of the contrast agent into bacteria.

"Most existing imaging probes target the bacterial cell wall and cannot access the inside of the bacteria, but maltodextrin-based imaging probes target a bacterial ingestion pathway, which allows the contrast agent to reach a high concentration within bacteria," said Murthy.

Maltodextrin-based imaging probes consist of a fluorescent dye linked to maltohexaose, which is a major source of glucose for bacteria. The probes deliver the contrast agent into bacteria through the organism's maltodextrin transporter, which only exists in bacterial cells and not mammalian cells.

"To our knowledge, this represents the first demonstration of a targeting strategy that can deliver millimolar concentrations of an imaging probe within bacteria," noted Murthy.