Agricultural Research Service microbiologist Maria T. Brandl has provided new evidence of the mostly mysterious interaction between nearly invisible animals called protozoa and Salmonella.
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, apparently can't 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 sanitize 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 sanitizing.
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.
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