Growth and Survival of Attached Listeria on Lettuce and Stainless Steel Varies by Strain and Surface Type

Abstract

The foodborne pathogen Listeria monocytogenes lives as a saprophyte in nature and can adhere to and grows on surfaces as diverse as leaves, sediment, and stainless steel. To discern the mechanisms used by L. monocytogenes for attachment and growth on various surfaces, we studied interactions between the pathogen on lettuce and stainless steel. A panel of 24 strains (23 of Listeria monocytogenes and 1 L. innocua ) was screened for attachment and growth on lettuce at 4 o C and 25 o C and on stainless steel at 10 o C and 37 o C. Overnight growth of attached cells resulted in a 0 – 3 log increase on lettuce, depending on the strain and the temperature. Among the worst performing strains on lettuce were two from a large cantaloupe outbreak, indicating that factors important for interactions with cantaloupe may be different from those required on lettuce tissue. Strains that grew the best on lettuce belonged to serotypes 1/2a, 1/2b, and 4b and were from cheese, potatoes, and water/sediment near produce fields. Confocal microscopy of L. monocytogenes tagged with constitutively expressed green fluorescent protein indicated associations with the cut edges and veins of lettuce leaves. On stainless steel coupons, there was a 5 – 7 log increase at 10 o C after 7 d and a 4 – 7 log increase at 37 o C after 40 h. Statistically, surface growth on stainless steel was better for serotype 1/2a than for serotype 4b strains, even though certain serotype 4b strains grew well on the coupons. The latter included strains that originated from produce and water/sediment. Some strains were fit in both environments, while others showed variability between the two different surfaces. Further analysis of these strains should reveal molecular factors needed for adherence and surface growth of L. monocytogenes on different biotic and abiotic surfaces.

The Listeria monocytogenes exopolysaccharide significantly enhances colonization and survival on fresh produce

“…It is also important to note that the majority of listerial biofilm studies involved manmade materials used in food processing, such as stainless steel, aluminum, rubber, glass, and plastics ( Blackman and Frank, 1996 ; Bonaventura et al, 2008 ; Lee et al, 2017 ). The extracellular biofilm matrices on these materials contain mostly eDNA and secreted proteins ( Blackman and Frank, 1996 ; Rieu et al, 2008 ; Harmsen et al, 2010 ; Ferreira et al, 2014 ; Guilbaud et al, 2015 ; Zetzmann et al, 2015 ; Oloketuyi and Khan, 2017 ; Rodríguez-López et al, 2018 ), and biofilm forming capacity is highly dependent on specific strains and experimental conditions ( Borucki et al, 2003 ; Cherifi et al, 2017 ; Lee et al, 2017 ; Gorski et al, 2021 ; Gray et al, 2021 ). The lack of EPS under these conditions is consistent with the results of this work that showed that Pss does not affect colonization of manmade materials ( Chen et al, 2014 ; Figure 1 ).…”