Imagine trying to count the raindrops on your car's windshield after
a light rain. That's what it can be like for a researcher to count Campylobacter
colonies growing in round petri dishes.
Historically, the medium, called agar, used to grow Campylobacter
contains blood components or charcoal, giving the agar a dark color.
Unfortunately, Campylobacter colonies are clear, often appearing
like water droplets on the agar.
Now, Agricultural Research Service
food technologist J. Eric Line has found a way to make the task of counting
them a whole lot easier.
Scientists typically use a technique called direct plating to isolate
and count microscopic organisms. "Direct plating can be used to
grow and count Campylobacter from a variety of sample types.
But distinguishing Campylobacter from non-Campylobacter
contaminants that often grow on many existing agars is difficult,"
Line has determined that exposing Campylobacter to low levels
of the chemical triphenyltetrazolium chloride does not harm growth,
yet stains the colonies deep red to magenta. New agars used for Campylobacter
growth are translucent, resulting in a contrast of dark colonies on
the translucent background. Line explains, "This greatly facilitates
Campylobacter isolation and makes counting them on light boxes
or by electronic means possible."
But contamination by other organisms can still happen. In this instance,
even if contaminant colonies show up as red, most of them are easily
distinguished from Campylobacter by differences in shape and
Campylobacter is a foodborne pathogen found in several raw or
mishandled foods, including poultry. More than 10,000 cases of human
campylobacteriosis are reported to the Centers for Disease Control and
Prevention each year, though many more cases go undiagnosed or unreported.
This illness is characterized by diarrhea, cramping, abdominal pain,
and fever. (See related articles on pages
The new technique, available for licensing, can be used in laboratories
to conduct diagnostic testing.By Sharon
Durham, Agricultural Research Service Information Staff.
Eric Line is
in the USDA-ARS Poultry
Microbiological Safety Research Unit, Richard B. Russell Agricultural
Research Center, 950 College Station Rd., Athens, GA 32604; phone (706)
546-3522, fax (706) 546-3771.
"Making Campylobacter Easier To Count" was published
in the October
2004 issue of Agricultural Research magazine.