Abstract
To the Editor: Because methicillin-resistant Staphylococcus aureus (MRSA) has been identified in retail meat worldwide (1–4), the potential exists for its transmission to humans. Of the various meat products surveyed, pork had the highest contamination rate in the United States and Canada (1,2), as did beef in Korea (3) and poultry in the Netherlands (4). The study in Korea also observed MRSA from chicken, which demonstrated sequence type (ST) 692 by multilocus sequence typing (MLST), a type distinct from that isolated in beef and pork. Despite sample size variations, these studies suggested that MRSA contamination in different meat categories can vary by location and that molecular distinction may exist among MRSA isolates in meat of different origin.
Generated Summary
This study investigated the prevalence and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) in retail meat samples collected from Detroit, Michigan, USA, between August 2009 and January 2010. The research involved collecting 289 raw meat samples from 30 grocery stores, including beef, chicken, and turkey. The study aimed to determine the extent of MRSA contamination in retail meat and to characterize the MRSA isolates found. The methodology included identifying presumptive S. aureus colonies, performing antimicrobial susceptibility testing, and characterizing isolates using various molecular typing methods such as pulsed-field gel electrophoresis (PFGE), SCCmec typing, and spa typing. The findings were then compared with previous studies to assess potential changes in MRSA prevalence and the emergence of specific strains.
Key Findings & Statistics
- A total of 289 raw meat samples were collected: 156 beef, 76 chicken, and 57 turkey.
- Sixty-five (22.5%) samples yielded S. aureus: 32 beef (20.5%), 19 chicken (25.0%), and 14 turkey (24.6%).
- Six samples were positive for MRSA: 2 beef (1.3%), 3 chickens (3.9%), and 1 turkey (1.7%).
- The study in Korea observed MRSA from chicken, which demonstrated sequence type (ST) 692 by multilocus sequence typing (MLST).
- In a previous study in the United States, the overall prevalence of S. aureus and MRSA was 40% and 5%, respectively.
- The only multidrug-resistant MRSA isolate in this study (MRSA1) was from beef and was resistant to β-lactams, macrolides, and fluoroquinolones.
- All 9 MRSA isolates belonged to USA300.
- Two distinct spa types were identified: t008 and t2031.
- spa type t008 was identified in 6 isolates of beef, chicken, and turkey origin.
- spa type t2031 was recovered from MRSA4a, 4b, and 4c from a chicken sample.
Other Important Findings
- The study found that the prevalence of MRSA in retail meat in Detroit was lower than in a previous study in the United States.
- The study identified two distinct spa types, t008 and t2031.
- The nucleotide variation in t2031 caused amino acid changes from glycine-asparagine in t008 to asparagine-lysine.
- All MRSA isolates in the study were USA300, suggesting a possible human source of contamination during meat processing.
- The 5-nt difference between t2031 and t008 implicates multiple MRSA clones in poultry.
Limitations Noted in the Document
- The study’s findings might have been influenced by the sampling seasons (August 2009–January 2010).
- Sample size variations in other studies made it difficult to compare MRSA contamination in different meat categories.
- The study’s findings may not be generalizable to other geographic locations due to the potential for different strains of MRSA to be present in different areas.
- The exclusion of pork might explain the lower prevalence of S. aureus and MRSA.
- The failure to identify ST398 in the US retail meat also indicates that the human MRSA clones might be better adapted in meat processing than ST398 in this country.
Conclusion
The study highlights the presence of MRSA in retail meat in Detroit, Michigan, with varying prevalence across different meat types. The lower prevalence compared to previous studies might be due to the exclusion of pork. The identification of USA300 as the predominant MRSA strain suggests a possible human source of contamination during meat processing. The presence of multiple spa types, including t008 and t2031, indicates the diversity of MRSA strains in retail meat. The findings underscore the need for continued monitoring of MRSA in the food supply and for further research to understand the transmission dynamics and potential public health implications of different MRSA strains. The identification of different spa variants and their potential links to different clinical outcomes raises questions about whether more spa variants are present in poultry or meat. The study’s findings suggest that variants with a meat origin might have different public health implications, thus highlighting the need for additional research to clarify this possibility. The study emphasizes the importance of continued surveillance to track MRSA strains and their potential impact on human health. The diversity of strains and the potential for human transmission underscores the importance of effective hygiene practices in meat processing to minimize MRSA contamination in the food supply.