Comparative susceptibility of planktonic and 3-day-old Salmonella Typhimurium biofilms to disinfectants

To compare the susceptibility of a 3-day-old biofilm and planktonic Salmonella to disinfectants at different exposure times. We hypothesize that Salmonella biofilms are more resilient to disinfectants compared to planktonic Salmonella. The susceptibility of planktonic cells to disinfectants was tested by a modified version of the Council of Europe suspension test EN 1276. Salmonella biofilms were formed using the Calgary Biofilm Device. Results show that 3-day-old Salmonella biofilms are less susceptible to the disinfectants benzalkonium chloride, chlorhexidine gluconate, citric acid, quaternary ammonium compounds, sodium hypochlorite (SH) and ethanol, compared to planktonic Salmonella. Surprisingly, the results also demonstrate that low concentrations of SH were more effective against a 3-day-old biofilm compared to high concentrations of SH. While all the disinfectants evaluated were able to reduce biofilm-associated cells at concentrations and contact times sufficient to eliminate planktonic cells, there were still sufficient viable cells remaining in the biofilm to cause further contamination and potential infection. Protocols for the use of chemical disinfectants need to include biofilm susceptibility testing. There is a requirement for an effective and standardized tool for determining the susceptibility of biofilms to disinfectants.