Maturation of pathogenic biofilms induces enhanced resistance against gaseous chlorine dioxide.

Biofilms are surface-associated microbial clusters embedded in extracellular polymeric substances (EPSs). Biofilms formed on food contact surfaces create challenges for the food industry due to their increased tolerance to antimicrobial agents and disinfectants. This study aimed to evaluate the effect of the biofilm maturation period on their resistance to gaseous ClO2. Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli O157: H7 biofilms formed on stainless steel (SS) and high-density polyethylene (HDPE) surfaces were investigated. The total cell mass and protein content significantly increased (P < 0.05) between the second and fifth day of maturation, and the biofilms' resistance to gaseous ClO2 increased as they matured. Generally, the cell counts of 0-day-old L. monocytogenes, S. Typhimurium, and E. coli O157: H7 biofilms on SS and HDPE reduced below the detection limit (0.48 log CFU/cm2) within 5 min. The cell counts of 2-day-old biofilms of the three pathogens were reduced by 6.22 to over 7.52 log, while those of 5-day-old biofilms were reduced by 3.64 to over 6.34 log after 20 min of treatment with 30 ppmv of gaseous ClO2. Therefore, as resistance increases with biofilm maturation, daily gaseous ClO2 treatment would maximize the antimicrobial efficacy of the cleaning strategy against biofilms.