Lynn Savage, email@example.com
ATHENS, Ga. – In the battle against the pathogens that lurk
on the carcasses of the animals we eat, sometimes the most difficult task is identifying
which tiny enemy you are fighting. Scientists at the US Department of Agriculture’s
Agricultural Research Service have developed a technique that allows them to identify
and isolate one major bacterial foe, Campylobacter, within 24 hours. The novel approach
uses hyperspectral imaging to distinguish Campylobacter targets from similar but
Shaped like puffy spiral staircases, members of the Campylobacter
family are a major cause of food-borne illness. They typically flourish in the guts
and waste of chickens, sheep, cattle and other animals, but can find themselves
in the bellies of unsuspecting people if the animals’ carcasses aren’t
processed and cooked appropriately. With millions of animals processed each year
for human consumption, the USDA and other regulatory bodies, as well as food producers
themselves, need a fast and accurate method for detecting Campylobacter.
Investigators at the USDA’s Agricultural Research Service are
using hyperspectral imaging to identify and isolate Campylobacter pathogens more
rapidly than standard plating techniques can. Courtesy of Seung-Chul Yoon.
The standard screening method for food-borne pathogens is to swab
the animal, add the collected residue to a petri dish prepared in a growth medium
such as agar, and then incubate the sample for up to 48 hours. Once bacterial colonies
have been established, someone must visually ascertain whether the result is Campylobacter
or something that looks like it. This adds time to the screening process.
At the Agricultural Research Service, Seung-Chul Yoon and his
colleagues have been working on hyperspectral imaging methods since the 1990s. Their
latest technique captures spectral information across a wide swath of wavelengths
for every pixel on an imaging array aimed at a target. In Yoon’s lab, the
target was petri dishes loaded with pure samples of Campylobacter along with other
microorganisms typically found on poultry carcasses.
The group’s hypothesis was that Campylobacter and various
other bacteria have just enough chemical differences that could be picked out by
reading their spectral signatures.
The researchers used a hyperspectral imaging system made by the
Institute for Technology Development at the John C. Stennis Space Center in Mississippi.
The CCD-based system features a diffraction grating spectrograph manufactured by
Specim Spectral Imaging Ltd. of Oulu, Finland. The group used a pair of 50-W tungsten
halogen lamps to light the samples, acquiring line scans of each sample; the diffraction
grating enabled them to acquire 256 spectra in the range of 400 to 900 nm –
at each of 640 pixels.
They found that the optimum wavelength to differentiate Campylobacter
from unrelated species was 503 nm when the bacteria were grown in blood agar and
501 nm when they were grown in Campy-Cefex agar. The technique worked with up to
99 percent accuracy, even when cultures were incubated for only 24 hours. They reported
their efforts in the journal Sensing and Instrumentation for Food Quality and Safety
in March 2010.
According to Yoon, whereas scanning in the 400- to 900-nm range
was enough to identify Campylobacter from among other bacteria, it could not differentiate
one subspecies of Campylobacter from another.
The next steps the group will take are designed to increase the
level of difficulty to approach real-world conditions.
“Our main efforts will be to establish a hyperspectral imaging
technique [that is] reliably sensitive and specific for mixed cultures and carcass
rinses with the 24-hour time window,” Yoon said. He added that the technique
also might be used to screen such pathogens as salmonella and Escherichia coli.