A National University of Ireland - Galway researcher has discovered the difficulties of removing salmonella after it was adhered to a surface for about a week, the university reports. The study was published in the Journal of Applied and Environmental Microbiology.

Microbiologist, Mary Corcoran, attempted to kill salmonella biofilms on various hard surfaces with three different types of disinfectants — even soaking the bacteria in disinfectant for 1.5 hours — but found the germs' viability unaffected by the chemical. Corocoran looked at the habits of salmonella biofilm on glass, stainless steel, glazed tile, concrete and plastic. It showed the biofilm of salmonella grows over time, and more firmly attaches to surfaces.

The study is considered a warning to food processing plants and other food services, who can not detect the bacteria before it has an opportunity to form biofilm on a surface.

"Food processing facilities must take strict care to keep salmonella out fo the clean areas where cooked foods get further processing and packaged, and ask whether disinfectants that are promoted as killing various types of bacteria are really as effective as claimed," Corcoran said. She added that good cleaning and appropriate food handling practices (such as regular hand washing) remained the best preventative measure to salmonella-induced illnesses.

The three disinfectants used against salmonella included sodium hypochorite (household bleach), sodium hydroxide, and benzalkonium chloride.

You can read the university statement, including what event prompted Corcoran's research, here.