Regeneration of bioifilms of Listeria monocytogenes and Ralstonia insidiosa 24 Hours Post-sanitizer Application Varies by Growth Temperature and Maturity
Lee, Ian
Lee, Ian
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Abstract
Listeria monocytogenes (Lm) contamination in dairy industry environments is a major source of concern due to its ability to co-colonize with other microbial species and form biofilms, protecting from traditional sanitizer treatment. We explored the differential efficacy of common sanitizer treatments on Lm biofilms alone and co-cultured with Ralstonia insidiosa (Ri) under dairy-processing conditions. Three Lm and two Ri strains were cultured in 1/20x tryptic soy broth (TSB) separately and in pairs on stainless steel coupons at both 11�C and 22�C. On days 1, 3, and 10, coupons were retrieved and treated with 600ppm sodium hypochlorite (SH) for 10 minutes or 400ppm quaternary ammonium chloride (QAC) for 3 minutes, or with sterile PBS. Biofilms were dissociated via sonication and vortexing, after which they were plated on Listeria Chromogenic Agar and 0.05X TSA with 1.5mg/L Crystal Violet for Lm and Ri enumeration, respectively. Sanitized coupons were placed in fresh 1/20X TSB and re-enumerated after 24 hours. A repeated measures ANOVA assessed the effect of maturity, temperature, bacterial strain, and sanitizer type on Lm counts after completing three separate experiments for each strain and strain combination. Log reduction of Lm and Ri was significantly reduced with increased biofilm maturity but was not influenced by Temperature or biofilm type (mono vs co-culture; P=0.45); Both sanitizers maintained strong inhibition (-4.2 LogCFU/cm� to +1.5 LogCFU/cm� reduction in Lm cells) 24 hrs post-treatment (P<2e-16), however, in older biofilms (day 10), especially at 22�C, this effect was significantly reduced (P=0.0004). SH achieved a greater log reduction across all conditions (p< 2e-16) but QAC maintained a stronger inhibition over 24 hours (P=0.0029). Older biofilms may not only resist killing but may regenerate more strongly after sanitation at processing temperatures.
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Date
1/1/2026
Student Status
Senior (Graduating in 2026)
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Poster
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microbiology
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College of Agriculture and Life Sciences
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Life Science