New York, January 8

reen Salads, long associated with good health, can cause food poisoning due to contamination with poisonous bacteria, according to a new research quoted by Nature magazine.

Vegetables fertilized with animal manure, containing pathogens, pose the biggest threat. Raw salad vegetables are now washed after harvesting to reduce the risk of contamination.

Apparently healthy green salads are sometimes contaminated with poisonous bacteria which even thorough rinsing would not remove. The researchers found that harmful bugs can enter lettuce plants through its roots and end up in the edible leaves.

It was after an outbreak of poisoning by the potentially fatal strain of Escherichia coli that was connected with pre-washed lettuce, that food microbiologist Kari Matthews and his colleagues at Rutgers University in New Jersey started investigating whether bacteria were getting inside the lettuce.

The team grew lettuce in manure inoculated with e. Coli.

After sterilizing the plants surface with bleach, the researchers still found bacteria within the internal tissues.