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, accordingly, The pathogens were in every major tissue, including the tissue that transports nutrients in plants..
Results 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 E. coli 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.
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. Moreover it is difficult to know where the pathogens were originally before the cutting took place.
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,
Through this procedure it was demonstrated that the bacteria was in the plant, moreover 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.