| dc.contributor.author | Malekmohammadi, Sahar | |
| dc.description.abstract | Foodborne pathogens are estimated to cause 48 million foodborne illnesses through consumption of contaminated food annually. Designing efficient control measures is vital to reducing foodborne illnesses. The modern trend toward preserving foods is using combinations of stresses (hurdle model). However, bacterial adaptation to one stress has the potential to increase resistance to subsequent stress, which is known as cross-protection. Due to recent outbreaks, contamination of ready-to-eat (RTE) foods by L. monocytogenes is a major food safety concern. L. monocytogenes nisin resistance increases when first exposed to NaCl and other stresses, such as low pH. In addition to environmental stressors, specific genomic elements can confer nisin resistance, such as the stress survival islet (SSI-1). We wanted to determine if SSI-1 was associated with salt-induced nisin resistance. Examining 48 L. monocytogenes strains when exposed to nisin and salt revealed that nisin resistance of L. monocytogenes strains increased when first exposed to NaCl. Deletion of SSI-1 demonstrated the role of SSI-1 in saltinduced nisin resistance. These data suggest that inducible nisin resistance in L. monocytogenes can be influenced by environmental conditions and the genetic composition of the strain, which should be considered when selecting control measures for RTE foods. Contamination of low moisture foods (LMFs) (aw <0.85) by Salmonella is a major concern, as Salmonella can survive for a long time on LMFs. A common method to control Salmonella on LMFs is thermal treatment. LMFs can be stored for long periods of time before thermal treatment. There is a possibility of cross-protection when Salmonella is exposed to low aw conditions followed by thermal treatment. 32 Salmonella strains were exposed to flaxseed for 24 weeks. Serovar Agona had a significantly lower death rate compared to Enteritidis and Montevideo (adj. p<0.05). At 24 weeks post inoculation, Agona had significantly higher thermal resistance than Enteritidis (adj. p<0.05). Specific genomic elements can confer osmotic resistance, such as proU and mgtC. ΔmgtC had a higher death rate than wild type. However, deleting proU did not change survival rate. This study broadens our knowledge about heterogeneity of bacterial responses to stressors, which will help to design efficient control measures. | en_US |
| dc.publisher | North Dakota State University | en_US |
| dc.rights | NDSU policy 190.6.2 | |
| dc.title | Heterogeneity in Phenotypic Response of Foodborne Pathogens to Control Measures | en_US |
| dc.type | Dissertation | en_US |
| dc.type | Video | en_US |
| dc.date.accessioned | 2019-05-17T17:17:49Z | |
| dc.date.available | 2019-05-17T17:17:49Z | |
| dc.date.issued | 2019 | en_US |
| dc.identifier.uri | https://hdl.handle.net/10365/29740 | |
| dc.description.sponsorship | North Dakota State University. Department of Microbiological Sciences | en_US |
| dc.description.sponsorship | USDA NIFA 2016-690003-24851 | en_US |
| dc.description.sponsorship | EPSCoR Doctoral Dissertation Award | en_US |
| dc.rights.uri | https://www.ndsu.edu/fileadmin/policy/190.pdf | |
| ndsu.degree | Doctor of Philosophy (PhD) | en_US |
| ndsu.college | Agriculture, Food Systems and Natural Resources | en_US |
| ndsu.department | Microbiological Sciences | en_US |
| ndsu.program | Molecular Pathogenesis | en_US |
| ndsu.advisor | Bergholz, Teresa M. | |
