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Title: Prevalence and characterization of Methicillin-resistant Staphylococcus aureus isolates from retail meat and humans in Georgia

Author
item Jackson, Charlene
item DAVIS, JOHNNIE - Former ARS Employee
item Barrett, John

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2013
Publication Date: 4/1/2013
Citation: Jackson, C.R., Davis, J.A., Barrett, J.B. 2013. Prevalence and characterization of Methicillin-resistant Staphylococcus aureus isolats from retail meat and humans in Georgia. Journal of Clinical Microbiology. 51(4):1199-1207.

Interpretive Summary: Staphylococcus aureus is a Gram-positive bacterium that can be commonly found on the skin or in the nasal passages of most humans and animals. It has been implicated in a number of diseases in humans ranging from minor skin infections to more serious infections such as pneumonia. Additionally, staphylococcal food poisoning, characterized by vomiting and diarrhea, is a leading cause of foodborne illness in the U.S. Food sources of S. aureus have recently expanded to include retail meat products from food-producing animals including swine, poultry, and cattle; there is increasing interest in the presence of Staphylococcus aureus, specifically methicillin-resistant S. aureus (MRSA), in retail meat products. In this study, staphylococci were isolated from retail pork and retail beef in Georgia and MRSA from the products were compared to human MRSA from the same geographic area. MRSA were recovered from 3% of retail pork, 4% of retail beef, and 50% of human samples and some MRSA were multidrug resistant. Using molecular analysis, three retail beef MRSA were identical to MRSA known to cause human infections. This study serves as an indication that staphylococci and MRSA are present on retail meat. This information is especially useful for consumers and personnel who handle raw meat as safe handling methods should be followed to avoid colonization with MRSA. It is also useful for scientists as they develop prevention and control strategies.

Technical Abstract: There is increasing interest in the presence of Staphylococcus aureus, specifically methicillin-resistant S. aureus (MRSA), on retail meat products. In this study, staphylococci were isolated from retail pork and retail beef in Georgia and MRSA from the products were compared to human MRSA from the same geographic area using broth microdilution antimicrobial susceptibility testing, Multilocus sequence typing (MLST), spa typing, SCCmec typing, and Pulsed-Field Gel Electrophoresis (PFGE). S. aureus was isolated from 45% (45/100) of pork products and 63% (63/100) of beef products; mecA was detected in S. aureus from both pork (3/100; 3%) and beef (4/100; 4%). Fifty percent (53/107) of human S. aureus also contained mecA. Multidrug resistance was detected among MRSA from all sources. All MRSA (n=57) were SCCmec type IV and nine different spa types were present among the isolates (t002, t008, t012, t024, t179, t337, t548, t681, and t1062). Four sequence types (ST5, ST8, ST9, and ST30) were detected using MLST; the majority of MRSA were ST8 followed by ST5. One retail beef MRSA was ST8 while the remaining three were ST5. In retail pork MRSA, ST5, ST9, and ST30 were observed. The majority of human MRSA were ST8. Thirty-seven MRSA isolates were pvl+, one of which was a retail beef MRSA. Using PFGE, three retail beef MRSA were identical in PFGE pattern, ST, and spa type to two human clonal MRSA (USA100 and USA300). One additional retail beef MRSA had a similar PFGE pattern to a human MRSA isolate, whereas none of the retail pork MRSA had similar PFGE patterns to human MRSA. This data suggests that the retail beef samples were contaminated from a human source possibly during processing of the meat and may present a source of MRSA to consumers and others who handle raw meat.