2007 Annual Report
1a.Objectives (from AD-416)
The host/pathogen interaction is poorly understood because establishment of an infection in livestock by a microorganism is a dynamic event. The complex interaction between the host and the pathogen can now be explored in more detail using microarrays. In this project, we will evaluate the genetic interaction of livestock and pathogenic bacteria during colonization in an attempt to elucidate and interpret the mechanistic roles of gene regulation in pathogenesis. Our goal is to develop a comprehensive knowledge of host/pathogen interactions during colonization and to elucidate how these interactions are affected by stress. These studies will lead to new and/or improved diagnostic techniques, new therapeutics and vaccines, and improved health management strategies for livestock.
1b.Approach (from AD-416)
Objective 1: Utilize microarray, microbiologic, and bioinformatic approaches in a ligated-intestinal model to elucidate host/pathogen genetic regulatory interactions during infection. Approach: We hypothesize that the pathogen, when introduced into the host environment, will regulate its virulence factors to adapt to the intestinal environment to achieve a colonized state. In turn, we expect the host will regulate its immune response at the site of infection to prevent or respond to the pathogen’s attempts to establish a foothold. We will utilize various molecular methods such as microarrays, in conjunction with a ligated intestinal model and directed colonization approach, to evaluate these interactions. Objective 2: Using two stress models (transportation and neuroendocrine) in conjunction with Salmonella challenge in swine, develop an understanding of the relationship between various forms of stress and food borne pathogen susceptibility and shedding. Approach: Our hypothesis is that an animal has differential physiological and immunological responses to various stressors. These responses are unique to the type of stress encountered or experienced. Therefore, different stressors differentially affect a host’s susceptibility to, and shedding of, food borne pathogens. We will expose pigs to two types of stress. We hypothesis the initiation of a stress response via peripheral CRH should have a negative influence that will lower the natural immunity of the host and increase susceptibility to pathogens. If our hypothesis is correct, then a lower infectious dose of pathogen will be required to induce infection and shedding. Objective 3: Model on-farm management practices to evaluate pathogen transmission in swine herds. Approach: The hypothesis is that there is a difference in pathogen transmission rates within swine herds which is dependent upon the type of housing system (group versus individual pens). This objective will be accomplished by experimentally infecting one individual within each type system and monitoring the spread of infection among the group. Individually, these separate transmission rates (pen or stall housing) can provide specific information on its particular system, but together these rates can be used in the future to design and generate more universal models and more appropriate rates for on-farm Salmonella herd transmission.
Livestock stress responses may activate mutation and adaptation in pathogens:
When livestock experience stress during such events as transportation or vaccination, the incidence of pathogen transmission seems to increase, and it's believed that this is a result of an interaction between the stress hormones produced in the animal and the pathogen itself. Using the stress neurochemical norepinephrine, ARS scientists in the Livestock Issues Research Unit at Lubbock, Texas, examined the expression of bacterial genes of Escherichia coli O157:H7 that promote the infection and transmission between food-producing animals and humans. They found that under stress, E. coli O157:H7 goes into a positive adaptive state in which the bacteria have an enhanced ability to mutate and adapt during active growth, allowing them to survive and thrive in new environments. This verifies that along with management strategies to minimize stress that the animals experience, we need to seek therapeutic methods to limit the effects of these stress hormones, particularly to minimize spillover of stress hormones into the gut, and thereby enhance the safety of our food supply. (NP108, Problem Statement 1.1.3)
Genetic changes at the cellular level during stress in pigs:
Pigs are exposed to various forms of stress during production that may influence their ability to respond to infection and consequently limit their overall productivity in a commercial setting. ARS scientists in Lubbock, Texas, in collaboration with researchers at Duke University, utilized a unique swine cell culture model to induce a stress response in porcine endothelial cells, allowing them to monitor cellular changes in gene expression using microarray technology. They found that under zero stress conditions, beneficial growth factors are expressed. However, they also observed that very little stress is required to promote negative cell responses that are associated with disease states. Genes were identified that can be targeted to moderate the negative health impacts of stress. By targeting such genes and minimizing their negative effects during times of stress, perhaps as part of management practices, we can promote healthier livestock. (NP108, Problem Statement 1.1.3)
Effect of temperature stress on virulence gene expression in Salmonella enterica Typhimurium:
The livestock and meat industry require improved methods to help eliminate pathogens in the nation's food supply. Many of the disinfection processes currently being used involve what are called environmental stressors, such as pH, nutrient starvation, high osmolarity, oxidative stress, and temperature fluctuations. However, these stressors may actually agitate the pathogens and make them more virulent. ARS scientists in Lubbock, Texas, in collaboration with researchers at the University of Arkansas, evaluated the effect of heat shock on virulence gene expression in Salmonella Typhimurium ATCC using microarray technology. They found that the high temperatures enhanced a wide variety of virulence and virulence regulatory genes by more than 100% compared to control. This clearly demonstrates the need to develop better management hurdles to eliminate pathogen contamination and growth in order to improve the safety of the American food supply. (NP108, Problem Statement 1.1.3)
Model system for evaluation of treatments designed to prevent invasion of Salmonella spp.:
Controlling foodborne pathogens such as Salmonella enterica involves reducing the amount of pathogen carried by the animals, often through use of antibiotics. Alternatives to antibiotic treatment are currently being developed, but gauging their effectiveness is difficult. ARS scientists in Lubbock, Texas, have developed an in-vivo model that allows them to evaluate the ability of a treatment to protect against Salmonella invasion within a 2.5-hour period. This model utilizes a ligated ileal loop and a newly engineered strain of Salmonella enterica that expresses a green fluorescent protein, providing quick evidence of change in pathogen levels following a treatment regime. The ability to rapidly screen probiotics, dietary modifications, neutriceuticals, and other feed additives will be a valuable tool for scientists and the livestock industry by providing faster development and testing of commercially viable alternatives to antibiotics. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
Stress affects Escherichia coli O157:H7 virulence genes in pigs:
In order to better control foodborne pathogens such as Salmonella enterica, it is essential that we better understand the mechanisms contributing to the pathogenicity of these pathogens. Using a newly developed ligated ileal loop surgical model on a population of pigs, ARS scientists in Lubbock, Texas, evaluated the genetic response of Escherichia coli O157:H7 during early stages of infection when the stress-associated catecholamine norepinephrine is present. The results in the in-vivo model showed repression of genes, including a set of phage shock genes, while induced transcripts included shiga-like toxins 1 and 2 and genes associated with lipopolysaccharide biosynthesis and iron transport. The model showed that norepinephrine-bacterial interactions previously identified in-vitro to affect a number of key virulence properties of E. coli O157:H7 also occur in vivo. These findings verify that this newly developed in-vivo model system can be an essential tool for researchers as they study the microbial endocrinology of E. coli O157:H7 pathogenesis. (NP108, Problem Statement 1.1.3)
Do some antibiotics promote a positive adaptive state in Salmonella enterica?:
Using antibiotics as part of livestock management practice is important to the sustainability of commercial livestock operations, but there are concerns that this practice induces the development of antibiotic resistance, making infections caused by resistant organisms difficult to treat. More research is needed to elucidate the molecular mechanisms that might promote the development of resistance. ARS scientists in Lubbock, Texas, in collaboration with Washington University and Texas Tech University researchers, evaluated gene expression in Salmonella during exposure to quinolone antibiotics. The gene expression profile showed that an error-prone DNA repair response was induced even though the bacteria continued to replicate. This genetic expression profile enhances the ability of the bacteria to generate mutations that might lead to the development of antibiotic resistance. This study provides genetic proof that chromosomal adaptation created by the selective pressure of a single antimicrobial drug (nalidixic acid) can result in multi-drug resistant strains of S. Typhimurium. Using this information, ARS scientists may now uncover ways to prevent the development of antibiotic resistance in foodborne pathogens when antibiotics are used as a vital therapeutic aspect of livestock production. (NP108, Problem Statement 1.1.3)
What makes Salmonella resistant to 5 different antibiotics?:
Development of multiple-antibiotic resistance in bacteria of food safety importance is a critical area of research since the need to use antibiotics to treat infections in livestock is mandatory for agricultural sustainability. Understanding the various genetic mechanisms that contribute to the development of such resistance is a high priority. ARS scientists in Lubbock, Texas, performed a study in collaboration with Washington University and Texas Tech University researchers to evaluate the genetic expression patterns of a multiple-antibiotic-resistant isolate of Salmonella enterica derived during antibiotic exposure from a wild type strain. Many important genetic systems were modified in the mutant isolate compared to its parent strain. These included porins, lipopolysaccharides, efflux pumps, and global regulatory mechanisms. Elucidation of these genetic mechanisms that contribute to antibiotic resistance will allow us to design and test better treatments as well as determine alternative drugs or adjuvants, such as the efflux pump inhibitory chemical CCCP, which may be used to prevent the development of resistance in pathogens. (NP108, Problem Statement 1.1.3)
|Number of invention disclosures submitted||3|
|Number of web sites managed||2|
|Number of non-peer reviewed presentations and proceedings||8|
Dowd, S.E. 2007. Escherichia coli O157:H7 gene expression in the presence of the catecholamine norepinephrine. Federation of European Microbiological Societies Microbiology Letters. 273:214-223.
Dowd, S.E., Killinger-Mann, K., Blanton, J., San Francisco, M., Brashears, M. 2007. Positive adaptive state: Microarray evaluation of gene expression in Salmonella enterica Typhimurium upon exposure to sub-therapeutic levels of nalidixic acid. Foodborne Pathogens and Disease. 4(2):187-200.
Himburg, H.A., Dowd, S.E., Friedman, M.H. 2007. Frequency-dependent response of the vascular endothelium to pulsatile shear stress. American Journal of Physiology - Heart and Circulatory Physiology. 293:645-653.
Widmer, K.W., Jesudhasan, P.R., Dowd, S.E., Pillai, S.D. 2007. Differential expression of virulence-related genes in a Salmonella enterica serotype Typhimurium luxS mutant in response to autoinducer AI-2 and poultry meat-derived AI-2 inhibitor. Foodborne Pathogens and Disease. 4(1):5-15.