Location: Livestock Issues Research
2006 Annual Report
Reduction in the pathogen load of animals prior to processing is an important component of the overall farm-to-fork food safety initiative and the ARS national program in food safety (NP 108) Problem Statement 1.1.3: Ecology, Host Pathogen, and Chemical Contaminants Relationships and the ARS Performance Measure 3.2.1, which indicates ARS will provide scientific information to protect animals from pests, infectious diseases, and other disease-causing entities that affect animal and human health. Pre-harvest food safety studies related to Problem Statement 1.1.3 need to include basic research to unravel the genetic interplay between the pathogen virulence factors and the host's immune system (Objective 1). By enhancing our knowledge of how the host combats infection with specific and important foodborne pathogens, we can target the immune system to enhance its ability to combat or resist infection with these pathogens. Building upon the first objective, we can add the additional variable related to stress on the animal's immune system and how this influences susceptibility to colonization with foodborne pathogens (Objective 2). Gaining applied knowledge on transmission rates of foodborne pathogens within production systems will add vital data necessary for model validation. Valid models will allow us to better evaluate at which point in production we must focus our efforts to develop alternative management practices (Objective 3). Only with the accumulation of functional genetic regulation data that is specific for a particular host/pathogen interaction can we develop improved therapeutic and management practices that reduce colonization, persistence, and shedding of these pathogens.
FY2007 Perform controlled infection studies in swine/Salmonella model. Begin stress studies to evaluate how different stressors influence pathogen shedding in swine.
FY2008 Perform controlled infection studies in bovine/O157 model. Continue swine studies and begin cattle studies evaluating stressors. Begin transmission studies in pigs.
FY2009 Evaluation and validation of microarray data. Continue studies in cattle to evaluate the effects of different stressors on pathogen shedding. Continue swine transmission studies.
FY2010 Finalize cattle stress studies. Finalize swine transmission studies.
Shiga-like Toxin II Expression: Is There a Less Dangerous Genetic Line of Escherichia coli O157:H7? ARS scientists in Lubbock, Texas, examined two separate lineages of E. coli O157:H7 for genetic factors that cause infection in humans and transmission from food to human hosts. Previous research points to a specific group or lineage of O157:H7 as potentially possessing more pathogenicity and transmissivity towards human hosts. This has potential significance to beef producers if one of these lineages can be conclusively proven as part of extensive future studies not to be of as great a concern and public health risk when they are found as meat contaminants. Several different methods were selected to investigate the difference in Shiga-like Toxin II (stx2) expression between the two lineages. It was conclusively shown that the lineage suspected of having less potential to be transmitted and cause disease in humans expresses significantly less toxin. In many cases, it was found that bacteria from this lineage is incapable of producing toxin. Although E. coli O157:H7 has many virulence factors and mechanisms to employ and evade host defenses, Stx2 production has been shown to be of high importance in relation to their pathogenicity, thus these findings are valuable in supporting the existence of two diverse lineages, one of which may be of less risk as a meat adulterant. A tremendous amount of research will be needed to fully evaluate the existence of a low pathogen lineage of O157:H7 and studies will be needed to ensure that these less pathogenic lineages cannot revert back to more dangerous phenotypes. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
How Does Multi-drug Antibiotic Resistance Develop in Salmonella enterica serovar Typhimurium? ARS scientists in Lubbock, Texas, in collaboration with collaborators at both Washington University and Texas Tech University, evaluated natural acquisition of antibiotic resistance in Salmonella enterica serovar Typhimurium that occurred through chromosomal mutations during low-level antibiotic exposure. A total of 30 nalidixic acid resistant isolates were derived from Salmonella Typhimurium DT104 ATCC 14028 by exposure to increasing concentrations of nalidixic acid. Eleven of these derivatives displayed multi-drug resistance for to up to 6 different antibiotics. The derivative strain that was resistant to 6 drugs had a profile of nalidixic acid, sulfisoxazole, tetracycline, chloramphenicol, cefoxitin, and streptomycin resistance. The results of this study indicate that natural chromosomal adaptation induced by the selective pressure of a single antimicrobial drug (nalidixic acid) can result in multi-drug resistant strains of S. Typhimurium and the mechanisms revealed may elucidate mechanisms that can prevent the development of antibiotic resistance in foodborne pathogens when growth promoting therapeutics are utilized on farms. Ultimately, this understanding should allow the USDA-ARS to develop novel methods to detect, predict, reduce, limit, or even prevent the arising of antibiotic resistant strains of bacterial pathogens. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
Understanding Genetic Mutations that Promote Antibiotic Resistance in Salmonella Typhimurium DT104. ARS scientists in Lubbock, Texas, in collaborations with Washington University, evaluated the chromosomal adaptations affecting gene expression and contributing to natural antibiotic resistance in Salmonella enterica Typhimurium DT104. Using an advanced genomics approach, it was found that the primary differences in expression were related to modulation of a type III secretion system (sse, ssa, and ssc genes), two cytochrome related transporters (cydCD), and important membrane transport genes. Repressed were systems involved in motility, chemotaxis, and transcripts involved in DNA damage responses. This genomics evaluation of changes and mutations that lead to the development of antibiotic resistance has improved our understanding of how natural antibiotic resistance occurs. Ultimately, this understanding should allow the USDA-ARS to develop novel methods to detect, predict, reduce, limit, or even prevent the arising of antibiotic resistant strains of bacterial pathogens. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
Virulence-related Gene Expression in a Salmonella enterica Serotype Typhimurium luxs Mutant in Response to Autoinducer AI-2 and Poultry Meat-derived AI-2 Inhibitor ARS scientists in Lubbock, Texas, in collaborations with the Texas A&M University, evaluated the modulation of genes related to virulence and how they are affected by natural inhibitors found in poultry meat. Poultry meat contains bacterial communication inhibitors that interfere with the bacterial communication hormone (AI-2) signaling and cause increases in genes that cause disease. Expression of 1136 disease-related genes in Salmonella Typhimurium wild type, and a mutant strain of this bacteria that is unable to produce communication hormone AI-2, were monitored in cells exposed to different treatments containing purified AI-2, cell-free supernatants (simulates AI-2-like activity), and the Natural Meat AI-2 Inhibitor. The results indicate that the inhibitor increases the expression of important disease causing genes (virulence factors). Understanding the interaction of AI-2 and AI-2 inhibitors found in poultry meat may explain Salmonella survival and potential increases in virulence on poultry products. The further classification of such naturally occurring AI-2 inhibitors and, more importantly how to counteract them, could limit the relative danger these pathogens pose when they contaminate our food supply. In addition, the transfer of knowledge gained from this research to preharvest food safety provides one of the more interesting potential therapeutics that can limit the colonization and proliferation of these pathogens in the animal by short circuiting their virulence systems. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
New Swine Surgical Model Allows for Evaluation of the Host-Pathogen Genetic Relationships We have developed a surgical model in swine that allows for evaluation of the genetic interactions of pathogens and the hosts during colonization. This model will provide novel data related to how animal hosts such as pigs and cows respond genetically to colonization by foodborne bacterial pathogens. This model is novel in that we can look at both the genetic responses for the host and the pathogen over time. By elucidating these genetic interactions, we can specifically define new targets for treatment and immune modulation that can limit the ability of these pathogens to colonize and cause infection in animals, thereby promoting production efficiency and the safety of the food supply. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
Shiga-like Toxin II Expression: Is There a Less Dangerous Type of Escherichia Coli O157:H7? We examined two separate lineages of E. coli O157:H7 for genetic factors that cause infection in humans and transmission from food to human hosts. Previous research points to a specific group or lineage (LI) of O157:H7 as potentially possessing more pathogenicity and transmissivity towards human hosts. As part of extensive future studies, this has potential significance to beef producers if one of these lineages can be conclusively proven not to be of as great a concern and public health risk when they are found as meat contaminants. Several different methods were selected to investigate the difference in Shiga-like Toxin II (stx2) expression between the two lineages. ELISA specific for Stx2, quantitative RT-PCR, and microarray results all showed dramatically and statistically lower levels of Stx2 expression in Lineage 2 (P < 0.05). Although E. coli O157:H7 has many virulence factors and mechanisms to employ and evade host defenses, Stx2 production has been shown to be of high importance in relation to their pathogenicity, thus these findings are valuable in supporting the existence of two diverse lineages, one of which may be of less risk as a meat adulterant and foodborne pathogen. A tremendous amount of research will be needed to fully evaluate the existence of a low pathogen lineage of O157:H7, and studies will be needed to ensure that LII isolates cannot revert back to more dangerous versions. (NP108, Problem Statement 1.1.3, ARS Performance Measure 3.2.1)
Dowd, S.E., Kim, S., Mateo, R., Yoon, I. 2006. Long term dietary supplementation of organic selenium enhances expression of immune related genes in adult pigs [abstract]. Federation of American Societies for Experimental Biology Conference Abstracts. Available: http://www.eb2006-online.com/pdfs/006709.PDF?PHPSESSID=f07543fef8761587d860af5e0239a3bf.
Dowd, S.E., Ishizaki, H. 2006. Microarray based comparison of two Escherichia coli O157:H7 lineages. BioMed Central Microbiology. 6:30.
Widmer, K.W., Jesudhasan, P., Dowd, S.E., Pillai, S.D. 2006. Gene expression in Salmonella enterica serotype Typhimurium luxS mutant in response to quorum sensing signals and a poultry meat-derived quorum sensing inhibitor using microarray-based studies [abstract]. In: American Society for Microbiology 106th General Meeting Abstracts, May 21-25, 2006, Orlando, Florida. 2006 CDROM. No. P-045.
Pareek, R.S., Bond, J., Watson, A., Dowd, S.E., McFadden, T., Kerr, D. 2006. Affymetrix GeneChip-based analysis of the genomic response to acute LPS-induced bovine mastitis [abstract]. 2nd International Symposium on Animal Functional Genomics, May 16-19, 2006, Michigan State University. Available: http://www.eb2006-online.com/pdfs/006709.PDF?PHPSESSID=f07543fef8761587d860af5e0239a3bf
Callaway, T.R., Morrow, J.A., Edrington, T.S., Genovese, K.J., Dowd, S.E., Carroll, J.A., Dailey, J.W., Harvey, R.B., Poole, T.L., Anderson, R.C. 2006. Social stress increases fecal shedding of Salmonella typhimurium by early weaned piglets. Current Issues in Intestinal Microbiology. 7:65-72.
Corapcioglu, M.Y., Vogel, J.R., Munster, C.L., Pillai, S.D., Dowd, S., Wang, S. 2006. Virus transport experiments in a sandy aquifer. Journal of Water, Air, and Soil Pollution. 169:47-65.
Callaway, T.R., Morrow, J.L., Johnson, A.K., Dailey, J.W., Wallace, F.M., Wagstrom, E.A., McGlone, J.J., Lewis, A.R., Dowd, S.E., Poole, T.L., Edrington, T.S., Anderson, R.C., Genovese, K.J., Byrd II, J.A., Harvey, R.B., Nisbet, D.J. 2005. Environmental prevalence and persistence of Salmonella spp. in outdoor swine wallows. Foodborne Pathogens and Disease. 2:263-273.