Making Campylobacter Easier to Count

A new agar gel has been developed by Agricultural Research Service (ARS) scientists to isolate and count hard-to-see, microscopic organisms that can cause food poisoning.

For researchers in the laboratory, counting the number of colonies of Campylobacter bacteria growing in round petri dishes can be like trying to count the number of raindrops on your car’s windshield after a light rain.

Historically, agar--the gel material used to grow Campylobacter in tissue culture--has blood components, or charcoal, as ingredients. These components give the agar a dark color. Unfortunately, Campylobacter colonies are clear, often appearing as water droplets on the agar. Now ARS food technologist J. Eric Line of the Poultry Microbiological Safety Research Unit in Athens, Ga., has found a way to make the task a whole lot easier.

Line has found that exposing Campylobacter to low levels of a chemical called triphenyltetrazolium chloride (TTC) was not detrimental to bacterial growth, yet imparted a deep-red to magenta color to the Campylobacter colonies. The new agars used for Campylobacter growth are translucent, resulting in a contrast of dark colonies on a translucent background. This contrast makes it easier for researchers to isolate and count Campylobacter. The new technology also allows researchers to count the bacteria on light boxes or electronically.

Campylobacter is a food-borne pathogen found in numerous raw or mishandled foods, including poultry. This illness is characterized by symptoms such as diarrhea, cramping, abdominal pain and fever. The agar can be used in laboratories to conduct diagnostic testing.

Read more about this research in the October 2004 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.