Survival of Listeria monocytogenesAttached to Stainless Steel Surfaces in the Presence or Absence of Flavobacteriumspp.

Contaminated surfaces of food processing equipment are believed to be a significant source of Listeria monocytogenesto foods. However, very little is known about the survival of Listeriain processing environments. In a mixed bacterial biofilm of L. monocytogenesand Flavobacteriumspp., the number of L. monocytogenescells attaching to stainless steel increased significantly compared to when L. monocytogeneswas in a pure culture. The L. monocytogenescells in the mixed biofilms were also recoverable for significantly longer exposure periods. On colonized coupons held at 15°C and 75% humidity, decimal reduction times were 1.2 and 18.7 days for L. monocytogenesin pure and mixed biofilms, respectively. With increasing exposure time, the proportion of cells that were sublethally injured (defined as an inability to grow on selective agar) increased from 8.1% of the recoverable cell population at day 0 to 91.4% after 40 days' exposure. At 4 and −20°C, decimal reduction times for L. monocytogenesin pure culture were 2.8 and 1.4 days, respectively, and in mixed culture, 10.5 and 14.4 days, respectively. The enhanced colonization and survival of L. monocytogeneson “unclean” surfaces increase the persistence of this pathogen in food processing environments, while the increase in the percentage of sublethally injured cells in the population with time may decrease the ability of enrichment regimes to detect it.