Even disinfectant won't kill Salmonella biofilms

Once Salmonella takes hold and forms a biofilm, it’s exceptionally difficult - if not completely impossible - to kill it, recent research shows.

Using three different types of disinfectant, researchers from the National University of Ireland, Galway, attempted to kill Salmonella biofilms on a range of hard surfaces.

“We found that it was not possible to kill the Salmonella cells using any of the three disinfectants, if the biofilm was allowed to grow for seven days before the disinfectant was applied,” said Mary Corcoran, a researcher involved in the study. The researchers found that even soaking the stubborn biofilms in disinfectant for an hour and a half failed to kill them.

The idea for the study came after the Agona serotype of Salmonella sickened 160 people in 10 countries across Europe. The outbreak was traced to meat from a major food-processing facility.

“It seems that Salmonella Agona entered into the environment in the part of the facility where meat that was already cooked was being handled and it had survived and contaminated the cooked meat,” says Corcoran.

“We were interested in determining if this particular Salmonella that caused the outbreak might have something special about it that makes it better at surviving in the environment of a food processing facility. Was it better at forming a dense biofilm or was it more resistant to disinfectants than other Salmonella?”

While the specific strain was found to be no more special than any other, the researchers found Salmonella is able to adopt a specialised biofilm on a range of surfaces, including glass, stainless steel, glazed tile and plastic. They also found that the biofilm gets denser over time and becomes more firmly attached to the surface.

Food processing facilities must take strict precautions to keep Salmonella out of clean areas where cooked food is further processed and packaged, Corcoran says.

“People need to question whether disinfectants that are promoted as killing various types of bacteria are really as effective in real-life situations where biofilms can form as they are claimed to be based on experiments that do not use biofilms,” said Corcoran.

“A lot of the time, the disinfectant may add very little, if anything, to good cleaning and appropriate food handling practices. There is a need for more research to define better methods for killing Salmonella biofilms.”

The study was published ahead of print in the journal Applied and Environmental Microbiology. The final version of the article is scheduled for the February 2014 issue of the journal.