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Staphlococcus aureus: Is Raw Meat a Risk Factor for Colonization and Infection?

Investigators
Smith, Timothy
Institutions
Kent State University
Start date
2013
End date
2016
Objective

Methicillin-resistant Staphylococcus aureus (MRSA) has been found in several recent studies investigating raw meat. Overall prevalence in meat samples has ranged from 2.5% to 11.9%. A recent study carried out in the United States found that 5% of meat samples tested in Louisiana were positive for MRSA, while 39.2% of samples were positive for any type of S. aureus. While S. aureus has previously been considered a food-borne pathogen, research examining S. aureus in food has largely focused on the toxins produced by food-borne S. aureus, and has not examined raw meats as a potential vector for colonization of consumers who handle raw meat products. Our central hypothesis is that S. aureus strains present on meat, including MRSA, may colonize individuals who handle raw meat. In order to investigate this hypothesis, we will carry out four specific objectives: 1) Determine the molecular epidemiology of S. aureus isolated from meat, humans, and the environment in two areas in Iowa. On the basis of our data presented under Preliminary Studies, our working hypothesis is that we will find a high diversity of strains, including isolates which are differentially distributed by source. 2) Model the spread of S.aureus in this population, and determine the risk attributable to food in the acquisition of S. aureus On the basis of our data presented under Preliminary Studies, our working hypothesis is that food has the potential to play a role in the transmission of virulent strains of S. aureus, similar to other environmental sources. 3) Determine the origin of food-borne S. aureus in order to examine the importance of contamination on-farm versus post-slaughter On the basis of our data presented under Preliminary Studies; our working hypothesis is that most meat isolates will originate from the farming environment, with typical "human" strains also playing a role in meat contamination. 4) Determine the effectiveness of an intervention derived from data collected in Aims 1-3. On the basis of the research carried out in Aims 1-3, we will develop, implement, and analyze an intervention designed to decrease the risk of acquisition of S. aureus from meat products.

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NON-TECHNICAL SUMMARY: Several recent publications have documented a high prevalence of S. aureus in meat products. We seek to expand upon this research and examine the epidemiology of S. aureus associated with raw meat, and determine the effect of meat contamination with S. aureus on human colonization. We hypothesize that humans are exposed to S. aureus from food animals via handling of foods of animal origin. We will test this hypothesis by carrying out four objectives: 1) Determine the molecular epidemiology of S. aureus isolated from meat, humans, and the environment in two areas in Iowa. We will accomplish this using a prospective cohort study in Iowa. 2) Model the spread of S. aureus in this population, and determine the risk attributable to food in the acquisition of S. aureus 3) Determine the origin of food-borne S. aureus in order to examine the importance of contamination on farm versus post-slaughter 4) Determine the effectiveness of an intervention derived from data collected in Aims 1-3. Our contribution will lead to an improved understanding of the epidemiology of S. aureus in the context of food-associated risk factors for human colonization. This contribution is significant as it will provide the knowledge needed to address the increasing public concern of MRSA acquisition from meat products; and to develop interventions on the farm or in the processing facility if food is found to be a risk factor for S. aureus acquisition, as hypothesized.

APPROACH: In order to carry out these objectives, we will perform a prospective study, enrolling 100 families and collecting nose and throat samples from participants on a weekly basis. We will also collect environmental samples from the homes of these participants. These samples will be analyzed for the presence of S. aureus. Raw, retail-available meat samples will be purchased from local grocery stores where study participants shop and also analyzed for the presence and quantity of S. aureus present on meat products. High hand-touch areas in local grocery stores and homes will also be swabbed in order to isolate environmental S. aureus. The prevalence of S. aureus carriage in human participants and contamination of meat products and shared environments will be determined, and all isolates will be subjected to molecular typing. Using this information, we will examine the relative prevalence of S. aureus strains found in our meat and human samples, and employ geographic information system (GIS) modeling to examine their distribution within the community. We will also use risk factor questionnaire data from our participants in order to determine possible community and occupational exposures to S. aureus. We will use these data to determine the attributable risk for acquisition of S. aureus from raw meat products. Finally, we will compare molecular types isolated from meat to our database of S. aureus isolates from humans and animals in order to determine the amount of meat contamination that originates from the farm versus post-slaughter contamination, and design and implement an intervention to minimize transmission of this organism. At the conclusion of this study, we expect to have determined the impact of contaminated meat on human colonization with S. aureus, and determined the origin (human versus animal) of meat contamination. These results will have important implications for public health policy, including whether to begin routine, nationwide surveillance for MRSA on meat products.

PROGRESS: 2013/08 TO 2014/08 Target Audience: Consumers, Farmers, Policymakers, Researchers, Public Health Workers, Veterinarians Changes/Problems: Nothing Reported. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? We have not disseminated our preliminary results yet. We plan to disseminate our findings via peer-reviewed journal article in near future. What do you plan to do during the next reporting period to accomplish the goals? During the next reporting period, We will be focused on addressing the special aim 2 of this project: Model the spread of S. aureus in the study population, and determine the risk attributable to food in the acquisition of S. aureus. We hypothesized that food has the potential to play a role in the transmission of virulent strains of S. aureus, similar to other environmental sources. Under this aim, we will develop a quantitative microbial risk assessment model following the standard paradigm of: hazard identification, dose-response assessment, exposure assessment, and risk characterization. A Geographic Information System (GIS) and associated methods of spatial analysis will be used to integrate the multiple sources of information hypothesized to be related to the likelihood a person has experienced increased risks of being colonized with S. aureus. We also will execute planned actions to achieve the specific aim 3rd of this project: To determine the origin of food-borne S. aureus in order to examine the importance of contamination on-farm versus post-slaughter. We plan to use whole genomic sequencing approach to carry out this mission.

IMPACT: 2013/08 TO 2014/08 What was accomplished under these goals? During this reporting period the research team members addressed the specific aim 1st of this project: To determine the molecular epidemiology of Staphylococcus aureus isolated from meat, humans, and the environment in Keokuk County and Iowa City, Iowa. In this period, we were focused on the molecular characterization of all human isolates positive for S. aureus. We enrolled 177 adults and 86 minors as a part of a prospective cohort study comprising 95 family units. Throat and nasal swabs from adults, and only nasal swabs from minors were collected on a weekly basis for a period of 1 year. A total of 3,119 isolates were resulted from 10,987 human samples. The overall prevalence of S. aureus among adults and minors was 33.8% (1736/5132) and 30.4% (713/2344) respectively. The overall prevalence of methicillin – susceptible Staphylococcus aureus among adults and minors was 32.5% (1669/5132) and 29.8% (699/2344) respectively. Likewise, the overall prevalence of methicillin-resistance Staphylococcus aureus (MRSA) among adults and minors was 1.3% (67/5132) and 0.6% (14/2344). The overall prevalence of the PVL gene was 0.8% (26/3119), and the overall prevalence of mecA gene was 2.6% (81/3119). The overall S. aureus prevalence was higher in Johnson County (37.3%) compared to Keokuk County (31.1%). All positive S. aureus isolates were subjected to spa typing. A total of 125 spa types were detected from 3,119 isolates. The most common spa types were t002 (n=345), t008 (n=248), and t216 (n=180). Upon the analysis of the spa data using the BURP algorithm, 10 and 7 clusters were observed in Keokuk County and Johnson County respectively. However, the number of spa types per cluster was observed higher in Johnson County. A subset of 725 isolates chosen by selecting all isolates received during the first week of each month was tested for MIC antibiotic susceptibility typing. We observed zero rates of resistance in most of the tested antibiotics. However, the adjusted resistance for erythromycin was 25.9% displaying the highest observed resistance. Quinupristin/dalfopristin had the resistance rate of 17.7%. All other antimicrobials had below 10% observed resistance rates. The study results indicate that majority of the population is capable of being colonized. It further indicates that strong environmental pressure and exposure to the pathogens may have been responsible for human colonization of S. aureus and MRSA.

Funding Source
Nat'l. Inst. of Food and Agriculture
Project source
View this project
Project number
OHOW-2013-07190
Accession number
1002648
Categories
Microbial Genetics
Parasites