A new Consumer Reports test found common indicators of poor sanitation and fecal contamination in pre-washed, bagged salad greens that were purchased before their use-by dates.
The March 2010 issue of the magazine says the relatively small sample – 208 containers representing 16 brands purchased at stores in Connecticut, New Jersey, and New York — did not find pathogens such as E. coli O157:H7, Salmonella or Listeria but the review did find problematic levels of bacteria.
“Several industry experts we consulted suggested that for leafy greens, an unacceptable level of total coliforms or enterococcus is 10,000 or more colony forming units per gram (CFU/g) or a comparable estimate. In our tests, 39 percent of samples exceeded that level for total coliforms and 23 percent for enterococcus,” the report said.
Coliforms and enterococcus are often used to gauge possible pathogen contamination.
Packages with higher bacteria levels had similarities, the report said. Many contained spinach and were one to five days from their use-by date. Packages six to eight days from their use-by date fared better.
Since 1993, at least 20 E. coli O157:H7 outbreaks have been traced to California-grown leafy greens – primarily lettuce and spinach. Most of these outbreaks involved packaged product that, despite several chlorinated washes, contained sufficient numbers of E. coli O157:H7 to cause infection at the time of consumption.
Although the exact E. coli contamination routes for these products remain unknown, contamination from the processing environment has been suggested. Researchers have different hypotheses, including these:
- Specific unit operations during processing of leafy greens, namely conveyance on a conveyor belt, dewatering by shaking or centrifugation, and mechanical shredding serve as important multi-directional transfer points for E. coli O157:H7 during processing of leafy greens.
- E. coli O157:H7 can penetrate into cut surfaces of leafy greens during processing.
