Growth promotant antimicrobials – gone. Over-the-counter feed-grade antimicrobials – going away. What’s next? On-farm antimicrobial data collection if Congress and the Food and Drug Administration (FDA) have their way. All this just to satisfy political whims. There have been no peer-reviewed scientific studies proving any harmful effects in humans associated with increased antimicrobial resistance resulting from the judicious use of antimicrobials in food-producing animals.
The FDA recently released the Executive Summary of the 2011 National Antimicrobial Resistance Monitoring System (NARMS) Report. Since its inception in 1996, NARMS has collected samples from people, animals at harvest, and retail meats from the grocery store. These samples have been analyzed for a series of foodborne pathogens, including non-typhoidal Salmonella, Enterococcus, Escherichia coli, and Campylobacter, to monitor for resistance to classes of antimicrobials important in human medicine. As they are the only national scientific studies of antimicrobial resistance patterns in foodborne bacteria, the livestock and poultry industries watch those reports carefully. As is usually the case, the 2011 report contained positive and negative findings.1 Here are some of the major conclusions:
During its 16-year history, NARMS has found Salmonella resistance to ciprofloxacin to be < 0.5% among human isolates, < 3% among retail meat isolates, and < 1% among animals at slaughter.
Continued rise in ceftriaxone resistance led to the April 2012 cephalosporin order of prohibition, which prohibits certain unapproved uses of cephalosporin drugs in cattle, swine, chickens, and turkeys.
In 2011, one human-source Salmonella isolate was resistant to both imipenem and cefepime and had a carbapenemase gene. No Salmonella isolates tested for imipenem resistance from any domestic animal source showed resistance or carbapenemase production.
Multiple drug resistant (MDR) Salmonella among human (9%), slaughtered chicken (8%), and slaughtered swine (16%) isolates in 2011 were the lowest since testing began.
Multiple drug resistant Salmonella increased from 6% in 2007 to 27% in 2011 among serotype I 4,,12:i:- isolates from humans, and among serotype Heidelberg isolates, MDR increased from 13% in 2006 to 34% in 2010, declining slightly to 30% in 2011. NARMS observed a decline in ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline (ACSSuT) resistance among Salmonella isolates from humans, swine, and cattle, and continued resistance levels of < 5% among isolates from retail poultry and poultry at slaughter.
ACSSuTAuCx resistance has remained below 5% among isolates from humans, retail poultry, poultry at slaughter, and swine since testing began. ACSSuTAuCx resistance is generally higher among cattle isolates at slaughter.
In 2011, 45% of Campylobacter jejuni and 36% of Campylobacter coli from human isolates had no resistance to any antibiotics tested in NARMS. There are no clear upward or downward trends observed among the human and poultry isolates.
In 2011, erythromycin resistance in C coli from human, retail chicken, and slaughtered chicken was at the lowest levels in several years (3%, 5%, and 3%, respectively). Campylobacter jejuni from humans and chicken sources has exhibited an erythromycin resistance rate of < 4% since NARMS testing began.
Since 2005, NARMS has observed no consistent decreases in ciprofloxacin resistance among C jejuni and C coli isolates from humans or chicken sources.
Gentamicin resistance among C jejuni isolates from humans, retail chicken, and chickens at slaughter was < 1% in 2011. However, between 2007 and 2011, gentamicin resistance among C coli increased from 0% to 12% among human isolates, 1% to 18% among isolates from retail chicken, and 1% to 6% among isolates from chickens at slaughter.
Ceftriaxone resistance among E coli isolates from retail chicken increased from 8% in 2002 to 13% in 2011; ground turkey isolates showed a larger increase (from 1% to 10%) during the same time period. This trend was similar in Salmonella. Resistance among isolates from slaughtered chicken also increased from 6% in 2000 to 12% in 2010, but dropped slightly to 9% in 2011. This was the first decline seen in the last 3 years.
All in all, I think it was a pretty positive report. However, one gap in this sampling strategy has been the inability to compare antimicrobial use on the farm to bacterial resistance patterns in animals pre-harvest. The results seen in harvest and retail meat samples may not accurately reflect actual on-farm exposure, hence the calls for on-farm data collection. The FDA is exploring ways to collect this antimicrobial use data. The US Department of Agriculture (USDA) has conducted a series of pilot studies to evaluate possible routes of collection as well. Congress, FDA, activists, and some retail establishments keep pressuring, and USDA seems willing to facilitate collection. The time has come for the industry to decide its position on providing government with access to on-farm records regarding the judicious use of antimicrobials in food-producing animals. We have an opportunity to participate in designing the program before it is designed for us.
1. 2011 NARMS Executive Report Summary. Available at: http://www.fda.gov/downloads/AnimalVeterinary/SafetyHealth/AntimicrobialResistance/NationalAntimicrobialResistanceMonitoringSystem/UCM407964.pdf. Accessed 16 September 2014.
-- Harry Snelson, DVM Director of Communications