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A combination of approaches is needed to reduce antibiotic resistance transmission along the food chain, including (i) judicious use of antibiotics (ii) targeted interventions for infection control, and (iii) communication of effective interventions to enable their broad-based implementation. These goals will be achieved through the following specific objectives: <P>
Objective 1. Develop, test and implement a dairy enterprise communication model that effectively identifies how information is obtained and used within complex dairy enterprises. <BR> Aim 1a. Identify dairy enterprises with herd sizes greater than 500 milking cows that represent the breadth of management styles for large dairy farms, and smaller farms at approximately the median U.S. herd size of 163. We will interview veterinarians, owners, herd managers, unit managers, and calf rearers to determine how animal care goals and decisions are communicated across the enterprise (with an emphasis on antimicrobial use). <BR> Aim 1b. Based on the interviews, we will develop a communication model that can be applied to complex dairy enterprises by animal health advisors to assess farm communication strategies and implement effective outreach and extension programs, including those designed to minimize the transmission of antimicrobial resistance. <BR> Aim 1c. Using existing science-based messages for minimizing the transmission of antimicrobial resistance, we will test the effectiveness of the communication models for complex dairy enterprises compared to existing outreach and extension strategies.<BR> Aim 1d. Based on results from Aim1c, modify communication model tools to align with field experience. <P>
Objective 2. Develop and evaluate calf rearing management practices that minimize transmission of resistant organisms and reduce antimicrobial selection pressure. <BR> Aim 2a. Test the hypothesis that pre-weaned dairy calves function as a site of amplification of multidrug resistant E. coli and Salmonella, and test an intervention to prevent this amplification. <BR> Aim 2b: Test the hypothesis that commingling of replacement heifers from multiple farms at offsite rearing facilities increases antimicrobial resistance within E. coli and Salmonella in heifers returned to the home farm. <BR> Aim 2c. Test the hypothesis that emergence of novel resistance genes in commensal fecal E. coli is more likely to occur in groups of calves with a higher prevalence of antimicrobial treatments. <P>
Objective 3. Quantify the overlap between genetic antimicrobial resistance determinants in the dairy production environment and in human disease. <BR> Aim 3a. Compare the array of antimicrobial resistance determinants in Salmonella isolated from dairy enterprises (clinical and non-clinical) and human clinical cases.
NON-TECHNICAL SUMMARY: Antibiotic resistance in food-borne bacteria is a serious public health problem and a major focus has been antibiotic use in animal agriculture. This project will utilize the dairy as a model system to study ways to address this problem. Previous research has shown that there are barriers to communication of prudent antibiotic use messages due to the size and complexity of larger modern dairies. We will investigate and evaluate effective ways of communicating these messages to all levels of workers on dairies of different sizes. We will also investigate ways to prevent the introduction of antibiotic resistant bacteria onto farms by measuring amounts of resistant bacteria where new animals are frequently purchased compared to farms where new animals are rarely or never brought onto the farm. We will also investigate the role of calf housing in spreading antibiotic resistant bacteria from older to younger calves by housing newborn calves away from older calves that are likely to shed resistant bacteria, and by increasing calf hutch cleaning. To assess the contribution of resistant bacteria from cattle to humans we will compare bacteria from both species to see if the genes in the bacteria that code for resistance are the same for both host species. Finally, we will use molecular biological techniques to identify bacteria with inactive resistance genes because those are more likely to occur in places where antibiotics are not used than in places where they are frequently used. This will be a way to identify specific sites on the farm where bacteria are being actively selected for resistance and thus will provide clues about how to prevent selection for resistance. Overall, this project will reduce resistance in disease-causing bacteria from cattle and provide valuable information for developing effective strategies for reducing antibiotic resistance on farms.
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APPROACH: Our approaches for completing these objectives include 1) an Extension component: interviewing dairy farm owner/operators, calf managers, and calf handlers, development of communication models for complex dairy enterprises, and testing the efficacy of educational messages on minimizing antibiotic resistance in dairies; 2) a Research component: applied research designed to test on-farm interventions targeting occurrence, dissemination, and persistence of antibiotic resistance, and comparing antibiotic resistance determinants in Salmonella isolated from bovine and human sources as a measure of the potential impact of bovine sources on human infection. These objectives will be accomplished by a multidisciplinary team with expertise in microbiology, epidemiology, genomics and molecular subtyping, social behavioral research and interview data collection and outreach and education. A Steering Committee, consisting of all collaborators as well as stakeholder representatives, will hold regular conference calls to provide input, discuss planning and progress, and address any issues that may arise. This committee will also participate in the planning of an initial stakeholder meeting and subsequent symposia and workshops that will facilitate planning and coordination of the project as well as dissemination of new knowledge generated. The steering committee will carry out overall project evaluation and each specific aim will also include an evaluation component. Objective 1 includes an evaluation component which will be designed as a clinical trial with the outcome being implementation of new protocols to minimize transmission of antimicrobial resistance. This clinical trial will evaluate the communication model for its effectiveness in identifying goals for minimizing antimicrobial resistance, effectiveness of information transfer within the dairy enterprise, effectiveness of creating change in management consistent with enterprise goals and science-based information. For Objective 2, the effectiveness of management interventions will be evaluated by comparing prevalence of resistant E. coli collected from each group using the appropriate statistical tests. Objective 3 will assess the extent of gene sharing between bacteria from human and bovine hosts. The outcome of Objective 3 as well as Objectives 1 and 2 will be evaluated during the course of manuscript peer review as well as inputs from the Steering Committee.