A study of environmental Listeria isolates from a dairy plant reveals a relationship of their genotypic variability with phenotypic expression and biofilm formation on clay brick floors

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 1






Listeria, environmental, biofilm


Listeria forms resilient biofilms in dairy plants. Three environmental Listeria isolates: L. monocytogenes (Lm), L. innocua (Li), and L. welshimeri (Lw), were compared for their cell surface properties, and biofilm formation on clay brick floors. For estimating cell attachment and biofilm formation, floor chips (1x1cm2) were immersed in sterile distilled water, containing 6 log cfu/mL of individual isolate, and held for 1h and 48 h at 22.4°C in a shaker incubator. The attached cells were retrieved using 3M sponge sticks and plated on brain heart infusion agar. Three trials were conducted, with samples drawn in triplicates, and the means were compared by ANOVA. For genetic analysis, the genomes were assembled using CLC Genomics Workbench. The water contact angle of clay brick chips, measured by Sessile drop device, was less than 90° (43.3 ± 0.78), indicating it to be hydrophilic and thus supporting Listeria attachment. The Lm and Lw resulted in a greater attachment than Li, also supported by their respective hydrophobicity values (20.13%, 21.15%, and 13.88%), as determined by hexadecane method. The zeta potential values, determined by Zeta sizer, were comparable (−15.8 mV, −16.2 mV, and −15.5 mv, respectively). The adhesion potential of isolates, as log counts, showed variability (Lm 2.91 ± 0.16, Li 2.73 ± 0.04 and Lw 2.89 ± 0.40) that exhibited itself in the biofilm formation: Lm (2.50 ± 0.14/cm2), Li (2.72 ± 0.26 /cm2), and Lw (3.32 ± 0.18/cm2). The presence of genes related to capsular glycan, cell wall/ capsular LTP, biotin biosynthesis, and carbohydrate metabolism, associated with amino sugars such as chitin, were correlated with biofilm formation of the 3 isolates. Whereas in the case of Lw, the presence of N- acetylglu- cosamine biosynthesis gene (NAG) was also detected. It is anticipated that biotin, chitin, and LTP genes might help the organism to colonize and NAG, when expressed, might interfere with biofilm formation resulting in sporadic presence of Lw as compared with Lm and Li. The study provides evidence that the initial attachment of Listeria species to floor surface is critical for biofilm formation.

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