Being able to quickly confirm the presence of infectious bacteria in a patient's bloodstream, and then identifying the specific species and strain, can make the difference between life and death for that patient. While traditional detection and identification methods are fairly accurate, they can also take too long to perform. A chemist from the University of Illinois, however, has developed an inexpensive new system that is much quicker – and it works by sniffing out the harmful bacteria.
Hospitals typically test for infectious bacteria by incubating blood samples in vials for 24 to 48 hours, at which point a carbon dioxide sensor in the vial indicates whether or not bacteria is present. After that, however, it is still necessary to determine what type of bacteria it is, and that process can take up to one more day. "In 72 hours they may have diagnosed the problem, but the patient may already have died of sepsis," said U Illinois' Prof. Ken Suslick.
To address the problem, Suslick developed a so-called "artificial nose." More specifically, it's a system incorporating cards printed with an array of 36 cross-reactive pigment dots, that change color as they detect chemicals in the surrounding air – chemicals such as those produced by metabolizing bacteria, which some microbiologists can distinguish between simply using their sense of smell.
To test the system, blood samples were applied to growth gels in Petri dishes, each dish having one of the arrays attached to the inside of its lid. The arrays were checked every half-hour, and the changes in the color of each dot were noted. Based on that data, all ten of the tested bacteria could subsequently be identified with 98.8 percent accuracy, by observing the unique sequence in which each of the dots changed color over time.
"We don't have an upper limit. We haven't yet found any bacteria that we can't detect and distinguish from other bacteria," said Suslick. "We picked out a sampling of human pathogenic bacteria as a starting point."
Not only does the system only take a few hours to produce results, while simplifying things by combining detection and identification into one step, but it is also able to indicate antibiotic resistance in bacteria.
The technology is now being improved, and will be commercialized through iSense, a company that Suslick co-founded.
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