Protozoa helps Salmonella survive chemical cleaning
to survive the treatments used by food processors to clean
equipment, according to a scientific study.
The study could lead to the development of new, more powerful, and more environmentally- friendly ways to reduce the incidence of Salmonellain meat, poultry and fresh produce, say the scientists at the US Agricultural ResearchService (ARS). It may also explain how Salmonella food poisoning still occurseven after the processor takes the required safety measures.
Salmonella is one of the food industry's most problematic food-poisoningbacteria. In 2004 the most frequently reported zoonotic diseases in humans were salmonellosis andcampylobacteriosis, with the most deadly being listerious, according to aEuropean Commission report. 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 aTetrahymena. The protozoan, after gulping down a species of Salmonella known as S. enterica, apparently can't digest and destroyit, according to laboratory tests by ARS microbiologist 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 wereencased 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 a10-minute bath of two parts per million of calcium hypochlorite, the bleachlike compound often used tosanitise 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, ARS stated in a press release.
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 thevacuoles. Those genes may be the ones that it activates when invading humans, she proposes.
There were 192,703 reported cases of salmonellosis and 183,961 of campylobacteriosis cases reported during 2004 in theEU, according to a European Commission report. The incidence of salmonellosis represent 42.2 cases per 100,000 population, which represents an increase of 22 per cent when compared with 2003, indicating the higher levels encountered in the new states.
European consumers have become increasing concerned about food safety, mainlydue to the bovine spongiform encephalopathy (BSE) scare in cattle beginning inthe late 1980s, a foot and mouth disease outbreak in 2001 and of avian flu in2003 and this year. Consumer concerns have in turn led to tougher regulatoryaction and increased survelliance of safety in food processing plants.
