Food Engineering

Packaged salads harbor indicator bacteria

March 8, 2010
Consumers Union urges FDA to set performance standards for greens.

A Consumers Union test of 208 packages of salad greens found no evidence of three pathogenic bacteria (E. coli O157:H7, Salmonella and Listeria) but did find other bacteria, known as indicator organisms (generic E. coli, Enterococcus and fecal coliforms), which public health officials say are signs of inadequate sanitation, fecal contamination or potential presence of pathogenic bacteria. The study, funded by the Pew Health Group, is entitled Bacteria and Bagged Salads: Better Standards and Enforcement Needed.

While the US government has standards for indicator organisms in milk, meat, drinking water and even swimming water, no federal standards are in place for these bacteria in salad greens, says the study. Several industry consultants suggest that an unacceptable level in leafy greens would be 10,000 or more colony-forming units per gram (cfu/g) or comparable measure, says the study.

For its analysis, Consumer Reports had an outside lab test 208 containers of 16 brands of salad greens, sold in plastic clamshells or bags, bought last summer from stores in Connecticut, New Jersey and New York. Among the findings:

  • 39% of samples exceeded 10,000 cfu/g (or another similar measure) for total coliforms, and 23% for Enterococcus;
  • 2% of samples exceeded French, and 5% of samples Brazilian, standards for fecal coliform bacteria;
  • Many packages containing spinach, including packages that were one to five days from their use-by date, had higher bacterial levels. Packages six to eight days from their use-by dates generally fared better;
  • Whether the greens came in a clamshell or bag, included baby greens, or were organic made no difference in bacteria levels;
  • Brands for which there were more than four samples, including national brands, plus regional and store brands, had at least one package with relatively high levels of total coliforms or Enterococcus.
According to Dr. Michael Hansen, Consumer Unions senior scientist, “The Senate should act immediately to pass pending FDA food safety legislation that requires the agency to set performance standards as well as develop safety standards for the growing and processing of fresh produce. FDA should also formally declare that certain pathogenic bacteria-such as E. coli O157:H7, Salmonella and Listeria-be considered adulterants when found in salad greens.”