Making Campylobacter Easier To Count

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," says Line.

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 structure.

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 2 and 4.)

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.