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Understanding the role of iron in biofilm formation, characterization, and viable but non-culturable state induction and resuscitation in Salmonella spp.

University of British Columbia

Non-typhoidal strains of Salmonella spp. are one of the greatest bacterial contributors to food-borne illness in Canada. Until the 1990’s, reports of food-borne illness were mainly associated with contaminated meat products; however, raw or minimally cooked produce is now being identified as a major source of food-borne outbreaks. Salmonella are able to persist on crop plants through biofilm formation, and existing in a viable but non culturable (VBNC) state; currently, little is known about the effect of iron on these processes. Using wildtype and iron mutants of Salmonella Typhimurium and Salmonella Enteritidis, the effect of iron was investigated. The first objective was to determine the effect of iron on Salmonella biofilm formation in vitro. Crystal violet (CV) biofilm assays, cell surface hydrophobicity assays, aggregation assays, motility, Congo red (CR) and calcofluor plates were used to characterize and quantify biofilm formation. In vitro work showed that the S. Typhimurium ton B mutant had significantly (p<0.05) greater hydrophobicity, significantly (p<0.05) reduced motility and biomass measured in the CV assay compared to the wildtype strain. The CR plates showed S. Enteritidis ton B mutant lacked curli, a key component, in its biofilm. The second objective was to determine the effect of iron on Salmonella biofilm formation on spinach using scanning electron microscopy (SEM) and CV biofilm assays. The SEM images showed the wildtype strains had stronger biofilm formation when compared to the ton B mutants; however, only the S. Enteritidis ton B mutant had reduced biofilm formation compared to the wildtype in the CV assays. The third objective was to determine the effect of iron on VBNC state induction and resuscitation of S. Typhimurium in vitro. To assess induction and resuscitation, 7% salt solution and nutrient broth supplemented with Ferrioxamine E were used, respectively. S. Typhimurium wildtype induced within 26 days and resuscitated within 22 hours, whereas, the ton B mutant did not. The results of this study suggest that iron does influence Salmonella biofilm formation, and VBNC induction. This study has further increased our understanding of how Salmonella can exist in the environment on plants with the potential to cause food-borne illnesses.

Text

2019-05-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/70018

Biochemistry and Molecular Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/