Friday, February 1, 2013

Prevalence and characterization of Methicillin-resistant Staphylococcus aureus isolated from retail meat and humans in Georgia.

Prevalence and characterization of Methicillin-resistant Staphylococcus aureus isolated from retail meat and humans in Georgia.

Jan 2013


Bacterial Epidemiology and Antimicrobial Resistance Research Unit, USDA-ARS, Russell Research Center, Athens, GA 30605.


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 (50/100) 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 beefMRSA. Using PFGE, MLST, and spa typing, 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 MRSAisolate, 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 ofMRSA to consumers and others who handle raw meat.