Foodborne bugs can infect plant tissues, immune to external sanitation

By Rory Harrington

- Last updated on GMT

Related tags Mung bean sprouts Escherichia coli Mung bean Salmonella

Amanda Deering and Robert Pruitt of Purdue University
Amanda Deering and Robert Pruitt of Purdue University
Disinfecting the outside of foodstuffs may be insufficient to eliminate the danger from pathogens after US scientists discovered that bugs such as E.coli and Salmonella can live inside plant tissue.

A study by researchers from Purdue University found that E.coli 0157:H7 was present in the tissue of mung bean sprouts and Salmonella in peanut seedlings after they contaminated seeds with pathogens prior to planting.

Seeds could be contaminated in this way before or after planting through tainted soil or water, said foodscience researcher Amanda Deering.

"The pathogens were in every major tissue, including the tissue that transports nutrients in plants,"​ she​said.

Results from her experiments were published in separate papers in the Journal of Food Protection and Food Research International.

The issue of E.coli contamination in sprouts has become a major food safety issue following the outbreak of a new 104:H4 strain in Germany that began in May 2011, killing 46 and sickening over 3,900.

The European Food Safety Authority (EFSA) last month said contaminated fenugreek seeds imported from Egypt were the likely cause of this outbreak and a much smaller one later in the summer in France.

Moving bacteria

Locating pathogens inside plants had been difficult because test methods involve slicing pieces from the plants which can cause the bacteria to move – either from the inside to the outside or vice versa, said Deering and botany professor Robert Pruitt.

The pair said it was difficult to know where the pathogens were originally before the cutting took place.

"The results are often imprecise because the methods allow bacteria to move,"​ explained co-author Pruitt.

A fixative was used to freeze the location of the bugs in the plant tissue before slicing occurred. A process called immunocytochemistry saw antibodies labeled with fluorescent dye that were then used to detect the pathogens,

"This shows us as close to what was in the plant when it was living as possible,"​ Deering said. "The number of bacteria increased and persisted at a high level for at least 12 days, the length of the studies."

After carrying out the freezing process, the scientist said hundreds of bacteria were detected in almost every type of tissue.

While proper sanitization eliminates Salmonella and E. coli​ from the surface of foods, this would not combat contamination of inner tissues, Deering and Pruitt said.

Only cooking those foods to temperatures known to kill the pathogens would eradicate them from inner tissues.

Related topics Food Safety & Quality

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