News - December 7, 2006

Thirsty dishcloth bacteria most cunning

A pathogen that colonises work surfaces and dishcloths, arms itself against gradual drying out by growing into an unusually large, ribbon-like organism, Wageningen microbiologists have discovered. In addition, the bacteria is becoming resistant to disinfectants such as bleach.

The Salmonella enterica serovar Enteriditis enters our houses mostly through eggs, and sooner or later ends up on the kitchen work surface. That’s where the problems start, according to Dr Rijkelt Beumer of the Food Microbiology Group. ‘If you have a stainless steel surface that you clean properly, then there's no need to worry. But if you leave damp dishcloths lying around or if there are scratches that stay wet for a while, then it's a different story, as there is a bigger risk of salmonella drying up slowly and adapting accordingly.’

Under the microscope it looks as though the rod-shaped bacteria gets bigger as it dries up, but this is not the case. Instead, it loses the ability to divide. New cells are made, but they do not split off. ‘This is called filamentation,’ explains Beumer. ‘In the lab it’s possible to grow salmonellas with fifty to a hundred cell nuclei. We don’t know why this happens. If the bacteria gets enough water, though, the new organisms do split off.’

The monster-salmonellas are resistant to bleach and once they have formed, they are more difficult to get rid of – useful information for the food industry and for households. Beumer’s group is now examining how effective filamentous bacteria are at infecting human gut cells. The research has been published in the Journal of Food Protection.