Biofilm recovery from chitosan action: A possible clue to understand Listeria monocytogenes persistence in food plants

Listeria monocytogenes is able to form biofilms on surfaces of food industry premises. Once established at certain plant sites, this pathogen can persist there for months or years, risking the transfer to raw materials or processed food by direct contact or other mechanisms. Though persistence of certain strains of L. monocytogenes isolated from food industry surfaces has been reported in several cases, experimental evidence has so far been inconclusive about the association of persistence to features such as better biofilm forming ability or higher resistance to disinfectants. This work has aimed at checking another possible cause of persistence, the ability to recover after exposure to antimicrobial compounds. Damaged cells in the biofilms formed by twelve L. monocytogenes strains previously isolated from an Iberian pig slaughterhouse and processing plant, six persistent and six non persistent, were compared in their recovery of viable cell counts during the 24 h following exposure to chitosan or peracetic acid. Persistent strains showed a better resuscitation rate after chitosan damage.