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P1-64 Influence of Biofilm Formation in the Resistance of Salmonella to Desiccation and Thermal Treatment in Wheat Flour

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Rossana Villa-Rojas , Washington State University , Pullman , WA
Juming Tang , Washington State University , Pullman , WA
Mei-Jun Zhu , Washington State University , Pullman , WA
Devendra H. Shah , Washington State University , Pullman , WA
Narayan C. Paul , Washington State University , Pullman , WA
Jie Xu , Washington State University , Pullman , WA
Introduction: Salmonella has several defense mechanisms to cope with stresses such as desiccation; biofilm formation has been reported as one. But most defense mechanisms tend to help cope with more than one type of stress; for example Salmonella Enteritidis pSB311 forms a biofilm that reportedly may make it resistant to disinfectants and high temperatures.

 Purpose: Assess the influence of biofilm formation in resistance to desiccation and thermal treatments of Salmonellain wheat flour.

 Methods: Seven strains of Salmonella Enteritidis were used, three strong biofilm formers (G3, MD4, and UK1), three weak formers (G2, MD9, P97) and a mutation of G1 (silenced CsgB gene involved in curly fimbriae formation). A lawn or biofilm of Salmonella, depending on the strain, was harvested with maximum recovery diluent (MRD), then pelletized, re-suspended in 3 mL of MRD and used to inoculate organic wheat flour (108 CFU/g). Inoculated samples were equilibrated to aw0.45 in a controlled humidity chamber. Aluminum cells were filled with 0.7g of flour, isothermally treated at 80°C in an oil bath, sampled every 5 min up to 20 min (triplicates), cooled, serially diluted and plated on Tryptic soy agar with 0.6% (w/v) yeast extract, 0.05% (w/v) ferric ammonium citrate, and 0.03% (w/v) sodium thiosulfate. Thermal resistance (D-values) was calculated using the first order kinetics model. Significant differences were analyzed with Kruskal-Wallis and Dunn’ tests (α=0.05).

  Results: D-value for strong biofilm formers (10.2-27.8 min, R2=0.78-0.89) was significantly higher (p<0.05) than weaker formers (3.1-8.0 min, R2=0.86-0.91), with a strong linear correlation (spearman ρ=1) between biofilm capacity and D value. Population was significantly reduced (-0.28 to -1.49 Log reduction) for all strains (p<0.05) after equilibration; with no significant influence of biofilm formation capacity.

 Significance: This study found evidence suggesting the influence of biofilm formation on thermal resistance of Salmonella, but not on desiccation survival.

Back to: Poster Session 1 – Laboratory and Detection Methods, Low-water Activity; Retail and Food Service Safety; Seafood; Communication Outreach and Education; Produce; Food Toxicology; Non-microbial Food Safety; Food Defense; Microbial Food Spoilage
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