Thesis (Ph.D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xiv, 182 p.; also includes graphics. Includes abstract and vita. Advisor: Ahmed E. Yousef, Dept.of Food Science and Nutrition. Includes bibliographical references (p. ).

Listeria monocytogenes is a human and animal pathogen responsible for severe and sometimes fatal infections. Several outbreaks have been associated with contaminated commercial foodstuffs such as raw milk, soft cheese, fresh and frozen milk, poultry, seafood, fruits and vegetable products. Currently, the official method recognized by the Government of Canada for the detection and isolation of L. monocytogenes can take up to six days without confirmation, which can require two more days. An approach based on molecular beacons that fluoresce upon hybridization was developed and tested to detect L. monocytogenes and the genus Listeria in food. Two different beacons were created: one specific to species L. monocytogenes (MG1) and another for the genus Listeria (MG2). Each of these molecular beacons was used with two separate sets of primers: MG1-1f/MG1-2r, MG1-7f/MG1-4r, MG2-2f/MG2-2r and MG2-3ft/MG2-2r. (Abstract shortened by UMI.)

This study examined some of the environmental, physiological, and genetic factors or mechanisms which contribute to L. monocytogenes’ desiccation survival under food processing conditions. Desiccation experiments were carried out on stainless steel coupons stored at 43% RH, 15°C. The level of initial contamination had no impact (p>0.05), whereas the presence of a mature biofilm, prior osmoadaptation, and the presence of salt (5%) and lard (20-60%) on the SS coupons significantly (p<0.05) increased the bacterium’s desiccation survival. An Lm568 transposon mutant library was constructed to screen for novel genes involved in desiccation survival. Fifteen tolerant and 16 sensitive desiccation mutants were sequenced. Interrupted genes involved in motility and FA membrane modification were the most common in tolerant mutants whereas energy and membrane transport related genes were the most recognized in sensitive mutants. Lastly, a spontaneous desiccation resistant Lm568 variant was isolated, emphasizing the importance of understanding desiccation tolerance for food safety.

The 16S/23S ribosomal RNA (rRNA) intergenic space (IGS) regions from pathogenic and non-pathogenic species (spp.) of Listeria were characterized by the polymerase chain reaction (PCR) and DNA sequencing. DNA sequencing data for the small rRNA IGS region showed that this IGS was approximately 244 bp in length and was highly homologous (95 to 99 %) in five of the six Listeria spp examined; ie., L. monocytogenes, L. innocua, L. seeligeri, L. welshimeri, and L. ivanovii. A lower degree of homology (91 to 94 %) was detected in the large rRNA IGS region (ca. 494 bp) of these species. The DNA sequence data was used to develop two sets of oligonucleotide primers for PCR-based detection of the members of the genus Listeria. The first set of primers were Listeria genus-specific and, the second set of primers were L. monocytogenes-specific. / xv, 131 leaves ; 29 cm.

Cryptic plasmids ranging from 2.0 to 10C kb in size were isolated from 25 out of 122 Listeria monocytogenes strains, and from 7 out of 11 strains of other Listeria species. / Of 2500 clones of a genomic library of L. monocytogenes 81-861 generated in Escherichia coli cells, 5 clones were identified in which $ beta$-hemolytic activity was stably expressed. Testing by intraperitoneal injection showed that these clones were lethal to mice. Restriction mapping of the inserts of the recombinant plasmids showed that, apart from a 650-bp internal Hind III fragment in 2 inserts, there were no other common sites. No homology was demonstrated between the DNAs of the inserts when Southern blots of restriction digests of the 5 plasmids were probed, though homology was demonstrated between the L. monocytogenes listeriolysin O gene and the DNA of one insert. The evidence suggests that at least one additional $ beta$-hemolysin, other than listeriolysin O, exists in this strain of L. monocytogenes, and that it may be a virulence factor. / Using a direct colony hybridization procedure on hydrophobic grid-membrane filters (HGMFs), the inserts of the recombinant plasmids were screened, and a DNA probe specific for L. monocytogenes was identified. After labelling with horseradish peroxidase and colour development of the chromogen, a commercial counter (HGMF Interpreter) was able to detect and count the organism electronically. When the efficacy of the chromogen-labelled DNA probe method on HGMFs was compared with the conventional method for three artificially-inoculated foods, there were no significant differences ($ alpha$ = 0.05) shown in the recovery of L. monocytogenes from the foods.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Food Science." Includes bibliographical references (p. 89-91).

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 142-164).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 170-192).

Thesis (Ph. D.)--Illinois State University, 2007. / Title from title page screen, viewed on July 16, 2008. Dissertation Committee: Radheshyam K. Jayaswal (chair), Brian J. Wilkinson, Anthony J. Otsuka, Wade A. Nichols, Laura A. Vogel. Includes bibliographical references and abstract. Also available in print.