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 the NARMS testing results for the June 2017 through May 2018 time period, their first full year of participation. This article summarizes the results for pork chops. Separate reports describe the results from poultry products and ground beef. The NARMS program looks for 3 different germs in retail pork chops. 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 pork chops 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, 36.7% (22/60) of the samples were positive, while 51.7% (31/60) contained Enterococcus. The prevalence of both of these bacteria were higher in pork chops purchased in North Dakota than those from South Dakota for both E. coli (48.0% vs. 28.6%) and Enterococcus (60.0% vs. 45.7%).
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 (1.2%). Prevalence rates for the indicator bacteria E. coli were similar between the 2017-18 Dakotas samples and 2015 national averages, while Enterococcus prevalence in pork chops was lower in the Dakotas samples compared to the 2015 national averages (51.7% vs. 81.7%).
Table 1. Prevalence of bacteria in pork chops from North and South Dakota grocery stores, June 2017-May 2018.
Antimicrobial resistance in bacteria from pork chops 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 time period of June 2017-May 2018; however, the resistance of germs found in pork chops during the period of February 2017 through May 2017 is summarized below (Table 2).
During this time period, none of the pork chop 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 isolate 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 pork chops, with 4 of them being MDR. Almost half (7/15) of these isolates were susceptible to all antimicrobials they were tested against. The drugs against which E. coli resistant strains were more commonly found included tetracycline, streptomycin, and ampicillin (26.7% of isolates resistant for each drug).
Fifteen Enterococcus isolates were obtained from pork chops during the same time period, with 4 of them MDR isolates. Every one (100.0%) of the 15 isolates was resistant to lincomycin, and 93.3% (14/15) of the isolates were resistant to tetracycline.
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 pork chops and other meat products in North and South Dakota. This year’s data indicates that Salmonella in pork chops is extremely uncommon 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 and certain indicator germs. As changes occur in the use of antibiotics in pork production, monitoring germ resistance to antibiotics will become important to determine the effect, if any, of shifts and declines in antibiotic use in pork production.