The researchers used a biofilm reactor to grow Salmonella biofilms and then tested the efficacy of three disinfectants, sodium hypochlorite, sodium hydroxide and benzalkonium chloride, against them. They tested both early (48 hours) and more established (168 hours) biofilms.
They found that all three chemicals reduced the viable count of Salmonella cells, but only sodium hydroxide could completely eradicate the early biofilm and none of the disinfectants could eradicate the mature biofilms, even after a 90-minute contact time. The ability to form resistant biofilms was shared by all the strains of Salmonella tested and they were able to colonise all surfaces, including glass, stainless steel and plastic.
The research team suggest that disinfectants used in food processing areas should be tested for their activity against mature biofilms. Researcher Mary Corcoran commented, “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.”
A report of the study will be published in the February issue of the journal Applied and Environmental Microbiology, but a copy of the manuscript can be found here.