This study measured and compared different temperatures and dwell times of hot water treatment on the reduction of Escherichia coli O157:H7 and Salmonella Typhimurium on beef carcass surfaces. Two different types of beef surfaces, lean and fat, were inoculated with a fecal slurry containing E. coli O157:H7 and S. Typhimurium at ca. 7-log CFU/g, washed to remove gross fecal matter, and rinsed with hot water between 66 and 82 degrees C (150 to 180 degrees F water) for either 5, 10, or 15 s. There were no differences (P > 0.05) in the log reductions of S. Typhimurium and E. coli O157:H7 on the lean surfaces for all three temperature treatments (66, 74, and 82 degrees C). Although the 15 s treatment resulted in a numerically higher log reduction than the other treatments, each of the times resulted in at least a 1 log reduction of both S. Typhimurium and E. coli O157:H7 for lean surfaces. For the fat surfaces, all time treatments for the 82 degrees C and the 10 and 15 s treatments for the 74 degrees C resulted in the highest log reduction for S. Typhimurium. The 5 and 10 s dwell times for treatments at 66 degrees C and the 5 s dwell time at 74 degrees C resulted in the lowest log reduction of S. Typhimurium and E. coli O157:H7. For E. coli O157:H7 all temperature and time treatments resulted in at least a 1 log reduction for the fat surfaces of the outside round. Therefore, hot water treatment is a proven method for reducing both coliforms and pathogenic bacteria.

Although the United States is considered to have one of the safest food supplies in the world, consumers have become increasingly alarmed with the subject of food safety as each crisis-related outbreak is scrutinized. With the onset of an agricultural-related food crisis, the media plays a vital role in publicizing both facts and opinions. Because of the relationship between agricultural risk communication and the media, it is essential to study the level of bias in the news reporting of these agricultural risk-associated events. The purpose of this study was to analyze the coverage and level of bias of the Salmonella outbreak associated with tomatoes in associated press (AP) newswires during a six-month period in 2008 through a descriptive content analysis. A comprehensive search yielded 57 usable articles written during a six-month period surrounding the outbreak; these articles were analyzed using the Hayakawa-Lowry News Bias categories. A total of 1,444 sentences were coded into nine categories: (a) report attributed, (b) report unattributed, (c) inference labeled, (d) inference unlabeled, (e) judgment attributed favorable, (f) judgment attributed unfavorable, (g) judgment unattributed favorable, (h) judgment unattributed favorable, and (i) other. Data indicated a significantly higher number of report sentences as compared to judgment sentences. Report sentences are considered both verifiable and factual. Thus, data indicated a low level of bias. Additionally, although journalists were objectively reporting information regarding the Salmonella outbreak, per capita tomato consumption for 2008 decreased. In the wake of a crisis, objective reporting is crucial. Journalists have an obligation to report information that is objective, factual, and verifiable. Understanding how the media tells agriculture‘s story can help bridge the gap between the industry and those reporting the issues.

Salmonella continues to threaten public health as well as negatively impact dairy producers on multiple levels. Efficacious solutions to control Salmonella among dairy cattle have long been sought to alleviate these problems. A novel vaccine technology has been developed based on purified siderophore receptors and porin proteins (SRP®) derived from Salmonella Newport. When vaccinated with these SRP® cattle are stimulated to produce antibodies which act in concert with host defenses to disrupt iron acquisition of pathogenic bacteria. To evaluate the effectiveness of this technology, a prospective cohort study was designed utilizing herds (n = 11) that practiced whole herd vaccination with the SRP® vaccine (vaccinated cohort) and herds (n = 11) that had not used the SRP® vaccine. Samples were collected during four rounds at approximately six week intervals from June through October 2009. Samples were transported to the laboratory at West Texas A&M University and cultured for the prevalence of Salmonella using selective enrichment methods. Salmonella isolates were evaluated for antimicrobial susceptibility and serotype. Data was analyzed using commercially available software to evaluate the herd-level effects of vaccination. Salmonella was ubiquitous throughout the Texas Panhandle and Eastern New Mexico, within-herd animal level estimates of prevalence ranged from 0.0 – 92%, over the length of the study period. Overall all rounds vaccinated herds had decreased (P = 0.012) Salmonella prevalence (15.3 vs. 27.5%). Vaccinated herds had numerically fewer Salmonella isolates belonging to the Newport serotype. Salmonella Typhimurium isolates were recovered approximately equally from vaccinated and non-vaccinated herds. Isolates from vaccinated herds were resistant to fewer antimicrobials throughout the study period. The ACSSuT(resistant to ampicillin, chloramphenicol, streptomycin, sulphisoxazole, and tetracycline) and MDR-AmpC (ACSSuT resistance plus resistance to ceftiofur and amoxicillin/clavulanate) resistant phenotypes were more frequently observed among non-vaccinated herds and none of the isolates from vaccinated or non-vaccinated herds were resistant to nalidixic acid, gentamicin, ciprofloxacin, or amikacin. These findings indicate vaccine efficacy for the reduction of Salmonella prevalence. Dairy operators along with herd veterinarians are encouraged to utilize this data with other herd specific factors in determining whether to use this specific vaccine.

The effect of heat shock was observed on the expression of hilA in Salmonella Typhimurium by creating a fluorescence-based reporter strain of Salmonella and by realtime reverse transcriptase polymerase chain reaction (RT-PCR). The hilA gene in Salmonella is known to play an important role in its pathogenesis. hilA is known to be activated when the bacteria encounter stress-inducing conditions. A number of factors have been identified that affect hilA expression, such as, pH, osmolarity, oxygen tension. When Salmonella enter their warm-blooded hosts, they encounter an increase in temperature. Therefore, heat is another stressor that is encountered by Salmonella during infection of their hosts. A fluorescence-based strain of Salmonella was created to study the effect of heat shock. The gene for green fluorescent protein (gfp) was placed under the control of the promoter of hilA on a plasmid. This plasmid was used to transform Salmonella cells to create a fluorescent strain. In this strain, when the hilA promoter is activated, gfp is transcribed, which encodes the green fluorescent protein. This protein can be measured by a fluorescence assay. The results of this study indicated that at 45ºC, hilA is activated. RT-PCR was used to look at hilA expression at different temperature. The results of this study indicated that, compared to 37ºC, higher temperatures like 45ºC and 55ºC significantly activate hilA.

One objective of the present investigation was to compare Salmonella and Campylobacter recovery incidence from commercially processed turkeys immediately prior to and following pre-chill and immersion chiller intervention strategies being used in three distinct turkey processing facilities. In each plant, on a single day of processing, 100 carcass rinse samples prior to and following each post-evisceration, pre-chill intervention and following immersion chilling were obtained for Salmonella and Campylobacter recovery. Two of three plants demonstrated a trend of decreased Salmonella on carcasses following the Inside Outside Bird Wash (IOBW), with reductions of 13%, and 11% being observed for Plants 1 and 2, respectively. Results for reductions of Campylobacter contamination were not as straightforward, with only Plant 3 showing decreased levels (11% reduction) following the IOBW. Plant 2 used an additional pre-chill intervention, a low pressure, acetic acid final wash, which was not shown to be effective in causing an additional reduction in either Salmonella or Campylobacter on carcasses. In all three plants, properly managed immersion chilling systems were the most effective microbial intervention for achieving Salmonella andCampylobacter reduction on processed turkey carcasses. While not as effective, the IOBW present in each plant likely contributed to the effectiveness of immersion chiller interventions. If managed properly these intervention points have demonstrated themselves as a viable means to effectively reduce Salmonella and Campylobacter on processed turkeys. Another objective was to modify the scalder environment to an alkaline pH and determine the effects of thermal killing of Salmonella and Campylobacter. In each plant, on a single day of processing, 50 carcass rinse samples prior to and following scald tank immersion and following feather removal were obtained for Salmonella and Campylobacter recovery. Modification of the scald water to alkaline conditions (pH 9- 10) did not result in increased thermal killing of Salmonella or Campylobacter on turkey carcasses, as hypothesized before the investigation. Alkaline conditions are known to facilitate a more efficacious pluck and aid in the detachment of bacteria. Due to this, the bacteria that were recovered at these points on the processing line could have had an impact on the observed data.

Salmonella outbreaks associated with orange juices have been reported in the past. Though there have been studies on the internalization of Salmonella into oranges there is inadequate information on the ability of this pathogen to survive on orange surfaces, become internalized, and survive the low pH internal conditions. The objective of this work was to study the survival of Salmonella gaminara and Salmonella agona on oranges obtained from the field and retail outlets and investigate their attachment and internalization potential. These studies showed that oranges obtained from both the field and retail outlets harbored relatively high concentrations of aerobic heterotrophic bacterial populations. There were significant differences in the survival of Salmonella agona and Salmonella gaminara at 4??C, room temperature (25??C) and 37??C. Survival was highest at 37??C and lowest at 4??C for both Salmonella gaminara and Salmonella agona. Salmonella agona and Salmonella gaminara showed significant differences in recovery when the cells were treated with pH 4.0, 7.0 and 9.5 buffers. The internalization studies suggest that a negative temperature differential favors the internalization of Salmonella cells into the fruit. Significant differences in the internalization of Salmonella into field and market oranges were observed with more internalization in the field oranges as compared to the market oranges. These results suggest that to prevent Salmonella contamination of orange juices adequate pre-harvest protection against pathogen contamination and post-harvest cleaning and disinfection strategies need to be employed.

Bacterias patógenas como Salmonella, habitantes naturales del tracto intestinal de diversos animales incluido el hombre, están comúnmente presentes en efluentes de desagües principalmente domésticos que desembocan al mar en forma directa o indirecta a través de ríos y acequias, llegando a constituir parte de la flora contaminante del litoral limeño y de los alimentos provenientes del mismo. La presencia de Salmonella está determinada por las condiciones biológicas y fisicoquímicas del ambiente acuático, que permiten su supervivencia, desarrollando mecanismos de adaptación como entrar a un estado de “viable no cultivable”, cambios metabólicos o alteraciones genómicas en respuesta a condiciones ambientales adversas. Debido a la importancia que tiene Salmonella en la incidencia de enfermedades gastrointestinales, se hace necesaria su vigilancia en el medio ambiente acuático para lo cual es preciso desarrollar estudios que faciliten el aislamiento, identificación y diferenciación de estirpes patogénicas en ambientes naturales. Muestras de agua de mar tomadas a lo largo del litoral limeño, durante los meses de marzo, abril y mayo del 2000, fueron procesadas para el aislamiento de Salmonella usando el método de filtración en membrana, pre-enriquecimiento en Agua Bufferada Peptonada; enriquecimiento selectivo en caldo Tetrationato, Selenito Cistina y Rappaport-Vassiliadis y posterior aislamiento selectivo en Agar XLD, Sufito de Bismuto, BPLS, SS, Hektoen y XLD. La identificación bioquímica se realizó mediante las pruebas de Oxidasa, Catalasa, Indol, Urea, TSI, LIA, Citrato y RM-VP. Para la identificación serológica se utilizaron sueros polivalentes agrupadores (A, B, C1, C2, D, E1 y E4), suero capsular Vi y flagelares de Salmonella choleraesuis. Se seleccionaron 203 estirpes oxidasa negativos, catalasa positivos, de las que 18 fueron identificadas como Salmonella choleraesuis, de las cuales 10 cepas fueron del serogrupo C1 y serotipo Salmonella Djugu y 8 del serogrupo D y serotipo Salmonella Enteritidis, una con bioquímica típica y 2 cepas atípicas incluidas en el serogrupo B de Salmonella choleraesuis, 3 cepas rugosas y 24 cepas con bioquímica típica que no aglutinaron con el suero polivalente empleado. Los perfiles de proteínas totales obtenidos mediante PAGE-SDS señalan diferencias de las cepas entre e intra serovar luego del análisis estadístico. El ADN cromosómico de los serotipos identificados fueron cortados con endonucleasas de restricción e hibridados con una sonda específica para el gen rDNA16S marcada por quimioluminiscencia. Se encontraron 4 ribotipos (RB, RC1, RC2 y RD), que correspondieron a cada serovar de Salmonella choleraesuis. / Pathogenic bacteria like Salmonella, natural inhabitants of the intestinal tract of diverse animals included the man, they are commonly present in effluents of mainly domestic drainages that discharge into the sea in direct form or through rivers and canals, ending up constituting part of the contaminate flora of the Lima´s coast and of the foods coming from the same one. Their presence is determined by the biological and physico chemical conditions of the aquatic environment that allow its survival, developing mechanisms of adaptation like to enter to state of “viable but no culturable”, metabolic and genomic changes in answer to adverse environmental conditions. Due to the importance that Salmonella has in the incidence of gastrointestinal illnesses, it becomes necessary their surveillance in the aquatic environment for that which is necessary to develop studies that facilitate the isolation, identification and differentiation of parthogenic strains in natural ecosystems. Seawater samples were taked along the Lima´s coast, during the months of march, april and may of 2000. For the isolation the membrane filtration method was used, pre-enrichment in Buffered Peptoned Water; selective enrichment in Tetrathionate, Selenite Cystine and Rappaport-Vassiliadis broths and selective isolation in XLD, Bismuth Sulfite, BPLS, SS, Hektoen, XLD agars. In the biochemical identification Oxidasa, Catalasa, Indole tests were used and it was cultivated in Urea, TSI, LIA, Citrato, RM-VP media. For the serologic identification grouping polyvalents (A, B, C1, C2, D, E1 and E4) and flagellars sera of Salmonella choleraesuis were used. 203 strains negative oxidase and positive catalase were selected, of which 18 were identified as Salmonella choleraesuis, inside those that 10 strains belonged to C1 serogroup and Salmonella Djugu serotype, and 8 to D serogroup and Salmonella Enteritidis serotype, one with typical biochemistry and 2 atypical strains typing inside the B serogroup of Salmonella choleraesuis, 3 rough strains and 24 with typical biochemistry that they didn't agglutinate with the polyvalent serum used. The profiles of total proteins obtained by means of SDS-PAGE point out differences of the strains inter and intra serovar after statistical analyses. The chromosomal DNA of the identified serotypes was cut with restriction endonucleases and hibridized with a specific probe for the gene rDNA16S marked by chemioluminiscens. They were 4 ribotypes (RB, RC1, RC2 y RD), that corresponded to each serovar of Salmonella choleraesuis.

Zugl.: Berlin, Freie Univ., Diss., 2009

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 110-127). Also available in electronic version. Access restricted to campus users.

Despite the development of various systems to generate live recombinant Salmonella Typhimurium vaccine strains, little work has been performed to systematically evaluate and compare their relative immunogenicity. Such information would provide invaluable guidance for the future rational design of live recombinant Salmonella oral vaccines. Here, a series of recombinant Salmonella Typhimurium strains were constructed to express either the enhanced green fluorescent protein (EGFP) or a fragment of the hemagglutinin (HA) protein from the H5N1 influenza virus, as model antigens. To investigate different delivery and expression methods, antigens were expressed from the chromosome, from high or low-copy plasmids, or encoded on a eukaryotic expression plasmid. Antigens were targeted for expression in the cytoplasm, or the outer membrane. In addition, combinations of two expression strategies were employed to evaluate the efficacy of combined delivery approaches. After investigating in vitro and in vivo antigen expression, growth and infection abilities, the immunogenicity of the constructed recombinant Salmonella strains was evaluated and compared in mice. Using soluble model antigen EGFP, my results indicated that vaccine strains with high and stable antigen expression exhibited high B cell responses, while eukaryotic expression or colonization with good construct stability is critical for T cell responses. For insoluble antigen model HA, the outer membrane strategy induced better B cell and T cell responses than cytoplasmic strategy. Most notably, the combination of two different expression strategies did not increase the immune response elicited as initially expected. Based on the advantages, deleterious or synergistic effects of different strategies identified in this study, I conclude that different construction strategies of recombinant Salmonella vaccine strains are needed for different forms of antigens (soluble or insoluble antigens). If the antigen (such as EGFP) is soluble and easily expressed in Salmonella, a low-copy plasmid-based strategy should be employed, as it can provoke both strong B cell and T cell responses with better plasmid stability. If a T cell response is preferred, a eukaryotic plasmid, or chromosome-based, cytoplasmic-expression strategy may achieve better results. For heterologous antigens that are likely to be expressed in an insoluble form inside Salmonella (such as HA), an outer membrane-targeting approach is recommended. In addition, I found that the combination of two expression strategies did not enhance the immune response, and hence I caution the use of such an approach. / published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy