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Salmonella discovery could help beat food poisoning

By Anthony Fletcher , 20-Feb-2006

The discovery that Salmonella might have an unwitting ally could lead to new ways of tackling food poisoning in meat and fresh produce.

Scientists at the Agricultural Research Service (ARS) in the US have found that Salmonella, one of the planet's most problematic food-poisoning bacteria, may be aided by transparent, nearly invisible animals called protozoa.

Microbiologist Maria T. Brandl has provided new evidence of the mostly mysterious interaction between these microscopic protozoa and Salmonella.

 

Brandls work at the ARSs Western Regional Research Centre in California could lead to more powerful and more environmentally friendly ways to reduce the incidence of Salmonella. Whats more, the EUs new regulatory environment could also help further developments in this field.

 

EU regulation No 853/2004, part of the package of hygiene laws that came into effect on 1 January, provides a legal basis to permit the use of a substance other than potable water to remove surface contamination from products of animal origin. Previously, such a legal basis did not exist in the bloc's legislation for red meat and for poultry meat.

 

During their lives, Salmonella bacteria may encounter a commonplace, water-loving protozoan known as a Tetrahymena. Brandl's laboratory tests showed that the protozoan, after gulping down a species of Salmonella known as S. enterica, cannot digest and destroy it.

 

So, the Tetrahymena expels the Salmonella, encased in miniature pouches called "food vacuoles."

 

The encounter may enhance Salmonella's later survival. Brandl found that twice as many Salmonella cells stayed alive in water if they were encased in expelled vacuoles than if they were not encased.

 

What's more, Brandl found that the encased Salmonella cells were three times more likely than unenclosed cells to survive exposure to a 10-minute bath of two parts per million of calcium hypochlorite, the bleachlike compound often used to sanitise food and food-processing equipment.

 

The research is the first to show that Tetrahymena expel living S. enterica bacteria encased in food vacuoles and that the still-encased, expelled bacteria can better resist sanitising. Brandl now wants to pinpoint genes that Salmonella bacteria turn on while inside the vacuoles. Those genes may be the ones that it activates when invading humans.

 

ARS is the US Department of Agriculture's chief scientific research agency.

 

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