Written collaboratively by Russ Daly, Alan Erickson, Laura Ruesch, Zachary Lau, and Deb Murray.
South Dakota State University is in its second year of participation in the National Antimicrobial Resistance Monitoring System (NARMS), with their Food Safety Microbiology (SD-FSM) lab (part of the Animal Disease Research and Diagnostic Laboratory in Brookings) working with the retail meat portion of the program. The SD-FSM tests fresh chicken, ground turkey, ground beef, and pork chops purchased in grocery stores in North and South Dakota, for the presence of certain germs. The germs identified are then further tested for resistance to common antibiotics that might be used in treating human illness.
The SD-FSM has recently compiled NARMS results for the period from June 2017 through May 2018, their first full year of participation. This article summarizes the results for ground beef. Separate reports will describe the results from poultry products and pork chops. The NARMS program looks for 3 different germs in ground beef. Salmonella is a significant cause of foodborne illness in the US, while the other 2 (generic E. coli and Enterococcus, found more routinely in meat products) are examined as indicator organisms for antibiotic resistance.
Prevalence of bacteria in ground beef from North and South Dakota grocery stores.
During the investigation period (June 2017 – May 2018), Salmonella was not identified in any of the 120 grocery store samples tested (Table 1). For E. coli, 45.1% (25/60) of the samples were positive, while 73.3% (44/60) contained Enterococcus. Results were similar between samples taken from North Dakota and those from South Dakota for E. coli prevalence, but higher in South Dakota for Enterococcus than in North Dakota (80.0% vs. 64.0%).
Since national statistics for the same time period aren’t yet available, it’s not possible to directly compare the Dakotas data with national data. However, information from 2015 – the most recent year available – showed that Salmonella levels were also quite low nationally (0.4%). Levels for the indicator bacteria E. coli and Enterococcus found in ground from stores in the Dakotas were lower than the 2015 national averages, which were 47.3% for E. coli and 87.7% for Enterococcus.
Table 1. Prevalence of bacteria in ground beef from North and South Dakota grocery stores, June 2017-May 2018.
|| 2015 National
Antimicrobial resistance in bacteria from ground beef from stores in North and South Dakota.
Isolates (individual growths) of the 3 germ species were submitted to the FDA for antimicrobial resistance testing. Data isn’t available yet for the June 2017-May 2018 time period; however, the resistance of germs found during the period of February, 2017 through May 2017 is summarized below (Table 2).
During this time period, none of the ground beef samples tested positive for Salmonella.
For the indicator organisms E. coli and Enterococcus, the action of 14 and 16 antibiotics respectively, is measured. A germ is classified as “Multi-Drug Resistant” (MDR) if it is resistant to 3 or more different classes of antimicrobials. During the February-May 2017 time period, 15 E. coli isolates were obtained from ground beef, with only 1 of them being MDR. The great majority (12/15) of these isolates were susceptible to all antimicrobials they were tested against; tetracycline (20% of isolates resistant) was the drug with the most resistance.
Fourteen Enterococcus isolates were obtained from ground beef during the same time period, with 4 of them MDR isolates. Antibiotic resistance of these gram-positive isolates was most commonly toward lincomycin and nitrofurantoin, with 85.7% and 42.8% of isolates resistant to these drugs, respectively.
Table 2. Antibiotic resistance in bacterial isolates from ground beef from North and South Dakota grocery stores, February-May 2017.
||# of MDR
South Dakota State University’s involvement with NARMS is off to a successful start. This year’s work has produced new information about the prevalence of potentially illness-causing germs in ground beef and other meat products in North and South Dakota. This year’s data indicates that Salmonella is extremely uncommon in ground beef purchased in the Dakotas, with no detections during the investigation period in either state. Comparing this 2017-2018 data with contemporary national data (once it’s available) will provide even better information regarding food safety in the Dakotas.
The project is also measuring levels of antibiotic resistance in those germs as well as certain indicator germs. As changes occur in the use of antibiotics in beef production, monitoring germ resistance to antibiotics will become important to determine the effect, if any, of shifts and declines in antibiotic use in beef production.