The prevention and control of salmonellae in commercial swine operations are becoming increasingly important. The current approach focuses on identifying sources and/or origins of salmonellae contamination before swine are processed for human consumption. The objective of the current study was to assess strain variability among salmonellae grouped by serotype and to determine common origins of contamination (farm or slaughter plant). Salmonellae were previously collected from swine at slaughter, serotyped by the National Veterinary Services Laboratory and stored at - 70??C. Pulsed-field gel electrophoresis (PFGE) was performed to genotypically characterize serotypic isolates using restriction endonuclease XbaI. Dendrogram comparisons were also used to assess genotypic similarity when multiple genotypes existed. This study found PFGE to be more discriminatory than serotyping indicating that multiple genotypic strains existed among selected serotypes. On the basis of PFGE results alone, origins of contamination could not be determined in this study. It is suggested by the author, that origins of contamination could be further defined pending future research, in which in-depth longitudinal studies are included. When used as an adjunct to conventional typing methods, PFGE may prove to be a substantial subtyping system in epidemiologic investigations to identify point-of-entry contaminants to the food chain.

The prevention and control of salmonellae in commercial swine operations are becoming increasingly important. The current approach focuses on identifying sources and/or origins of salmonellae contamination before swine are processed for human consumption. The objective of the current study was to assess strain variability among salmonellae grouped by serotype and to determine common origins of contamination (farm or slaughter plant). Salmonellae were previously collected from swine at slaughter, serotyped by the National Veterinary Services Laboratory and stored at - 70??C. Pulsed-field gel electrophoresis (PFGE) was performed to genotypically characterize serotypic isolates using restriction endonuclease XbaI. Dendrogram comparisons were also used to assess genotypic similarity when multiple genotypes existed. This study found PFGE to be more discriminatory than serotyping indicating that multiple genotypic strains existed among selected serotypes. On the basis of PFGE results alone, origins of contamination could not be determined in this study. It is suggested by the author, that origins of contamination could be further defined pending future research, in which in-depth longitudinal studies are included. When used as an adjunct to conventional typing methods, PFGE may prove to be a substantial subtyping system in epidemiologic investigations to identify point-of-entry contaminants to the food chain.

Invented in the 1950s, gel electrophoresis has now become a routine analytical method to verify the size of nucleic acids and proteins in molecular biology labs. Conventional gel electrophoresis can successfully separate DNA fragments from several base pairs to a few tens of kilo base pairs, beyond which a point is reached that DNA molecules cannot be resolved due to the size independent mobility. In this case, pulsed field gel electrophoresis (PFGE) was introduced to extend the range of DNA fragment sizes that can be effectively separated. But despite the incredible success of PFGE techniques, some important drawbacks remain. First, separation time is extremely long, ranging from several hours to a few days. Second, detection methods still rely on staining the gel after the run. Real time observation and study of band migration behavior is impossible due to the large size of the PFGE device. Finally, many commercial PFGE instruments are relatively expensive, a factor that can limit their accessibility both for routine analytical and preparative use as well as for performing fundamental studies. In this research, a miniaturized PFGE device was constructed with dimension 2cm x 2.6cm, capable of separating DNA fragments ranging from 2.5kb to 32kb within three hours using low voltage. The separation process can be observed in real time under a fluorescence microscope mounted with a cooled CCD camera. Resolution and mobility of the sample were measured to test the efficiency of the device. We also explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization was performed during gel electrophoresis and the extension length, entanglement probability and reorientation time of different conjugates were measured to study their effect on DNA migration through the gel. Finally, electrophoresis of DNA conjugates was performed in the miniaturized PFGE device, and shaper bands were observed compared with the non end-labeled sample. Furthermore, by end-labeling DNA with quantum dots, the migration distance of shorter fragments is reduced, providing the possibility of separating a wider range of DNA fragment sizes on the same gel to achieve further device miniaturization.

Invented in the 1950s, gel electrophoresis has now become a routine analytical method to verify the size of nucleic acids and proteins in molecular biology labs. Conventional gel electrophoresis can successfully separate DNA fragments from several base pairs to a few tens of kilo base pairs, beyond which a point is reached that DNA molecules cannot be resolved due to the size independent mobility. In this case, pulsed field gel electrophoresis (PFGE) was introduced to extend the range of DNA fragment sizes that can be effectively separated. But despite the incredible success of PFGE techniques, some important drawbacks remain. First, separation time is extremely long, ranging from several hours to a few days. Second, detection methods still rely on staining the gel after the run. Real time observation and study of band migration behavior is impossible due to the large size of the PFGE device. Finally, many commercial PFGE instruments are relatively expensive, a factor that can limit their accessibility both for routine analytical and preparative use as well as for performing fundamental studies. In this research, a miniaturized PFGE device was constructed with dimension 2cm x 2.6cm, capable of separating DNA fragments ranging from 2.5kb to 32kb within three hours using low voltage. The separation process can be observed in real time under a fluorescence microscope mounted with a cooled CCD camera. Resolution and mobility of the sample were measured to test the efficiency of the device. We also explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization was performed during gel electrophoresis and the extension length, entanglement probability and reorientation time of different conjugates were measured to study their effect on DNA migration through the gel. Finally, electrophoresis of DNA conjugates was performed in the miniaturized PFGE device, and shaper bands were observed compared with the non end-labeled sample. Furthermore, by end-labeling DNA with quantum dots, the migration distance of shorter fragments is reduced, providing the possibility of separating a wider range of DNA fragment sizes on the same gel to achieve further device miniaturization.

No description available.

Abstract not available

Staphylococcus aureus is one of the most important pathogens both in community- or hospital-acquired infections. The first part of this study analyzed the similarity of molecular types of S. aureus isolates cultured from nares and blood in patients with S. aureus bacteremia (SAB) by pulse-fielded gel electrophoresis (PFGE) of digested chromosomal DNA by Sma I at Kaohsiung Veterans General Hospital from August 1, 2000 through July 31, 2001. The results showed that the PFGE types of 78 (82.1%) paired nare and blood isolates of the 95 SAB patients having nasal carriage of S. aureus were clonally identical; identical in 89.7% patients of nosocomial group and 62.9% in community-acquired group. This provides the powerful evidence in close relationship between nasal carriage of S. aureus and acquisition of it in bacteremia. The data also showed that the rate of methicillin resistance occurred in SAB patients with nasal carriage in isolates of nosocomial SAB was 85.3%, and 31.3% in community-acquired group. The second part of this study analyzed the distribution of PFGE types of 163 nosocomial SAB isolates. The most predominant type was type A and composed 51.5% (84 strains) of 163 nosocomial SAB isolates. They were further divided into 7 subtypes. The second prevailing type was type B, 6.1%(10 strains). The evidence that an endemic stain (type A) occurred in >50% of nosocomial bacteremic isolates demonstrates horizontal dissemination of a single endemic strain of S. aureus in the SAB patients was common in the hospital. These results provide support for strategies to endorse more intensive procedures in infection control and to prevent systemic S. aureus infections by eliminating S. aureus nasal carriage.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 120-126). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 120-126). Also available on the Internet.

This thesis presents results from three studies conducted in a veterinary teaching hospital (VTH). Study 1 retrospectively examined a collection of enterococci from clinical infections. Five recurring strains of Enterococcus faecium, and one strain of Enterococcus faecalis were identified using pulsed-field gel electrophoresis (PFGE) as causing clinical infections. Study 2 examined the gastrointestinal tract enterococci as a source of enteroccocal infections in dogs. Enterococcal catheter-associated bacteriuria (CA-bacteriuria) rate was 8%. In 3 of 4 sets of bacteriuria and rectal isolates, CA-bacteriuria isolates were indistinguishable from rectal isolates suggesting that the patient’s fecal enterococci represented the infection source. In all 3 sets of wound and rectal isolates, fecal carriage of the infection isolate was observed. Study 3 examined the prevalence of bacterial species and the overall CA-bacteriuria rate. CA-bacteriuria rate was 24%, with Enterococcus spp., E. coli, Staphylococcus spp., Streptococcus spp. and Enterobacter spp., as the most prevalent bacteria in listed order. / PetTrust