Sprouts found in Canadian grocery stores home to scores of bacteria: Study
By Randy Shore, Postmedia News June 23, 2011
VANCOUVER — A University of B.C.-led study of micro-organisms on domestic produce found detectable levels of bacteria on 93 per cent of samples of sprouts taken from grocery stores across Canada.
Sprouts are grown in a warm, moist environment for three to five days, a perfect breeding ground for bacteria, said lead researcher Kevin Allen, a UBC food microbiologist, who likens the risk associated with eating commercially grown sprouts to consuming uncooked seafood.
Although the enterococcus bacteria detected on the sprouts poses no direct threat to health, the growing conditions that allow it to thrive can also encourage the growth of more harmful bacteria, such as E. coli and salmonella.
Nearly 80 per cent of sprout samples — including bean, alfalfa, broccoli, garlic and onion — showed microbial loads too numerous to count. Herbs, salad greens and spinach showed far fewer positive results and generally lower microbial loads.
Allen's produce testing revealed that seven per cent of fresh herb samples and two per cent of sprout samples contained a generic non-deadly form of E. coli, while about half of all samples of herbs, spinach, sprouts and leafy greens contained detectable levels of coliform, which may indicate fecal contamination of soil or water.
The distribution and concentration of enterococcus in the sprouts was much higher than expected, Allen said. Samples of produce were collected from grocery stores in five Canadian cities in March.
A deadly outbreak of a previously unseen variant of E. coli on sprouts in Germany this month puts an exclamation mark on the potential risks. More than 30 people died and up to 4,000 people were sickened in 13 countries as a result of the contamination.
Earlier this year, sprouts were recalled from Walmart stores in British Columbia, Alberta and Saskatchewan due to contamination with salmonella. In 2010, a massive recall was initiated for ready-to-eat salads from California that sickened 30 people due to E. coli contamination. Contaminated mung bean sprouts sickened 650 people in Ontario in 2005.
Kansas State University food safety professor Doug Powell, a collaborator with Allen, has recorded 38 outbreaks of illness associated with the consumption of raw sprouts over the past 20 years.
Once rare, contamination events involving fresh produce are increasingly common, said Allen.
"Thirty years ago, less than one per cent of all outbreaks of food-borne illness were associated with produce; now 14 per cent of outbreaks are linked to produce," he said. Increased packaging and handling of salad items and water contamination by cattle both play a significant role in the rise in outbreaks.
Allen warns that the very young, the very old and anyone whose immune system is compromised should avoid eating uncooked sprouts.
The deadly strain of E. coli that killed dozens of people in Germany has only been seen a handful of times before and represents a significant new threat, said Allen. The bacteria look just like relatively benign strains of E. coli, but this new strain appears to have acquired genes that transformed it into a shiga-toxin producing bacteria, Allen said.
"It really represents a new food-borne pathogen," he said.
The Canadian Food Inspection Agency ramped up testing of produce imported from the European Union in response to the crisis. All the results to date are negative.
"From a consumer's perspective, if produce is contaminated when it comes into the household, there is almost nothing they can do short of cooking it that will reduce or eliminate that risk," said Allen.
Sprouts are often consumed raw in salads or on sandwiches.
Allen's group is studying enterococcus because of its ability to incorporate DNA that leads to new drug resistant strains of the bacteria.
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