US breakthrough in Campylobacter detection
colonies of the food poisoning bacterium Campylobacter.
In labs, scientists typically use a technique called direct plating to isolate and count microscopic organisms, but it can often be difficult to differentiate between campylobacter and other micro 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," said Agricultural Research Service (ARS) food technologist J. Eric Line.
However, Line discovered that while exposing Campylobacter to low levels of the chemical triphenyltetrazolium chloride does not harm growth, it 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.
"This greatly facilitates Campylobacter isolation and makes counting them on light boxes or by electronic means possible," said Line.
However, contamination by other organisms can still happen. In this instance, says Line, 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. It is the leading bacterial cause of human gastroenteritis in the US, with 40,000 cases and approximately 680 deaths documented annually.
Doses as low as 500 organisms have been reported to cause illness - equivalent to one drop of raw chicken juice. Campylobacter is routinely found in cattle, sheep, swine, and avian species.
There are several species of Campylobacter (C. jejuni, C. coli, C.lari and C. uppsaliensis) capable of causing human illness. C. jejuni is implicated in approximately 85 per cent of the cases with the remaining 15 per cent being caused by C. coli. These are referred to as thermophilic Campylobacters, being able to grow at 37oC - 42 oC.
A comprehensive review of Campylobacter in poultry processing, published earlier this year by scientists from North Carolina University, suggested that avian species are the most common host, probably because of their higher body temperature. Research has shown that Campylobacter reach their highest populations on poultry during the warmer months when up to 97 per cent of samples tested were positive for C. jejuni. However Campylobacter outbreaks have also been associated with raw milk, contaminated water and contact with pets and farm animals.
The new testing technique, available for licensing, can be used in laboratories to conduct diagnostic testing. The discovery was first published in the October 2004 issue of Agricultural Research magazine.
