A new contrast agent based on maltodextrin has been developed at Georgia Tech that can provide in vivo imaging of bacteria with a sensitivity two orders of magnitude greater than previously achieved.
Unlike most previous methods, the new probes are able to enter bacterial cells by pretending to be food, while avoiding being ingested by the mammalian cells.
From Georgia Tech:
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.
In experiments using a rat model, the researchers found that the contrast agent accumulated in bacteria-infected tissues, but was efficiently cleared from uninfected tissues. They saw a 42-fold increase in fluorescence intensity between bacterial infected and uninfected tissues. However, the contrast agent did not accumulate in the healthy bacterial microflora located in the intestines. Because systemically administered glucose molecules cannot access the interior of the intestines, the bacteria located there never came into contact with the probe.
They also found that the probes could detect as few as one million viable bacteria cells. Current contrast agents for imaging bacteria require at least 100 million bacteria, according to the researchers.
In another experiment, the researchers found that the maltodextrin-based probes could distinguish between bacterial infections and inflammation with high specificity. Tissues infected with E. coli bacteria exhibited a 17-fold increase in fluorescence intensity when compared with inflamed tissues that were not infected.
Additional laboratory experiments showed that the probes could deliver large quantities of imaging probes to gram-positive and gram-negative bacteria for internalization. Both types of bacteria internalized the maltodextrin-based probes at a rate three orders of magnitude faster than mammalian cells.
Abstract in Nature Materials: Maltodextrin-based imaging probes detect bacteria in vivo with high sensitivity and specificity