The study could lead to the development of new, more powerful, and more environmentally- friendly ways to reduce the incidence of Salmonella in meat, poultry and fresh produce, say the scientists at the US Agricultural Research Service (ARS). It may also explain how Salmonella food poisoning still occurs even after the processor takes the required safety measures.
Salmonella is one of the food industry's most problematic food-poisoning bacteria. In 2004 the most frequently reported zoonotic diseases in humans were salmonellosis and campylobacteriosis, with the most deadly being listeriosis. Eggs, poultry meat and pork are the major sources of human Salmonella infections.
During their lives, Salmonella bacteria may encounter a commonplace, water-loving protozoan known as a Tetrahymena. The protozoan, after gulping down a species of Salmonella known as S. enterica, apparently cannot digest and destroy it, according to laboratory tests by ARS microbiologist Dr Maria Brandl.
The Tetrahymena then 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.She also 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 bleach like 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 and colleagues Sharon Berk of Tennessee Technological University-Cookeville and BenjaminRosenthal at ARS documented their findings in a recent issue of Applied and Environmental Microbiology.
Brandl is now attempting to pinpoint genes that Salmonella bacteria turn on while inside the vacuoles. Those genes may be the ones that it activates when invading humans, she proposes.