Date of Award
Master of Science
James S Dickson
Methicillin-resistant Staphylococcus aureus, commonly referred to as MRSA, first emerged from Staphylococcus aureus in the 1960's as an organism that was resistant to beta-lactam antibiotics such as penicillin. MRSA is able to colonize the skin, mouth and nares of both humans and animals without causing disease. However, if the bacteria gains entry via a cut or other skin abrasion, it can lead to more serious infections such as pneumonia, meningitis and septicemia. The three main types of MRSA infections currently recognized are hospital associated (HA), community associated (CA) and livestock associated (LA).
Recently, MRSA has also been discovered in retail meat products in the United States and other countries throughout the world. This discovery has raised concerns about the possibility of food being a vehicle for MRSA transmission and infection. It has been reported that MRSA can be found in meat processing facilities at any stage of production. Many studies have determined that pork and swine production are the major MRSA reservoirs. The current understanding of how MRSA may be transmitted in the food chain is limited thus preventing proper risk assessment to identify potential hazards to food handlers as well as to consumers.
The purpose of this research is to estimate the percent transfer of MRSA from retail pork products to food contact surfaces (cutting board or knife) and to estimate the risk of consumer exposure to
MRSA via contact with contaminated products and contaminated food contact surfaces. In order to simulate how these events may occur; pork products were obtained from a local supplier and inoculated with a 4 strain MRSA mixed culture at levels of 10, 100, 1,000, 10,000 and 100,000 CFU/ ml. Products were then analyzed to obtain initial bacterial populations. All products were vacuum- packaged and stored at 5°C for 2 weeks to simulate normal packaging and distribution. After 2 weeks, products were aseptically removed from the vacuum package and exposed to the transfer surfaces via 2 methods: light exposure to assess the percent transfer of MRSA from product to surface and heavy exposure to assess human exposure from contaminated products and surfaces. In light exposure, samples were laid on the transfer surfaces at room temperature for 5 minutes without any additional weight on the product and allowed to sit at room temperature before analysis. In heavy exposure, samples were laid on the transfer surface and a 500g lead donut was placed on top of the product as it was moved across a defined area of the transfer surface. The transfer surfaces then sat for 5 minutes at room temperature before being analyzed.
It was found that MRSA not only survived on the pork products during 2 weeks of cold storage but was able to transfer to food contact surfaces. This was true for all products tested across all 5 cell concentrations. These results suggest that even when cell concentration is low (≤ 10 CFU/cm2) human exposure is possible. Even though MRSA may only be present in very small quantities, more research is needed to determine the infectious dose of MRSA that may be in meat products in order to establish a risk assessment. Public education on safe raw meat handling and cooking practices should be continued as well as education of food handlers until there is a better understanding of the infectious dose of MRSA in raw meat products.
Heather L. Snyder
Snyder, Heather L., "Determination of transfer of methicillin-resistant Stapylococcus aureus from retail pork products onto food contact surfaces and the potential for consumer exposure" (2012). Graduate Theses and Dissertations. 12469.