Inactivation and induction of sublethal injury of Listeria monocytogenes in biofilm treated with various sanitizers

• The effects of five sanitizers on a L. monocytogenes biofilm was elucidated.
• Phenolic-based and QACs-based sanitizers most effectively reduced L. monocytogenes in a biofilm.
• L. monocytogenes cells enhance their persistence when they were multiply exposed to sanitizers.
• Biofilm cells experienced cell membrane damage when they were exposed to phenolic-based and QACs-based sanitizers.

This study determined the effects of different sanitizers (one phenolic-based, one chlorine-based, two QACs-based and one levulinic acid and SDS-based) on Listeria monocytogenes biofilm. The induction of the sub-lethal injury state and the biofilm formation characteristics as a result of exposure to sanitizers were also evaluated. The results revealed that QACs-based and phenolic-based sanitizers most effectively reduced L. monocytogenes, resulting in a reduction of 3.7–6.9 log CFU/ml and 4.9–8.2 log CFU/ml after a 60-min treatment for 37°C- and 15°C-grown biofilms, respectively. An enhanced level of sanitizer resistance was observed in biofilms when they were multiply exposed to QACs-based and phenolic-based sanitizers, with a reduction of 0.7–3.5 log CFU/ml and 1.6–>9.3 log CFU/ml for 37°C- and 15°C-grown biofilms, respectively. As biofilm cells became less sensitive, especially to QACs-based sanitizers, an increase in the percentage of sublethally injured cells was observed to the levels dependent upon sanitizer concentration. Confocal laser scanning microscopy (CLSM) analysis revealed that biofilm cells experienced cell membrane damage when exposed to QACs-based and phenolic-based sanitizers, providing more protection to cells located inside the biofilm matrix. This study highlights the ongoing need for improvement in intervention methods to control L. monocytogenes in food processing plants.