In several categories, the incidence of antibiotic-resistant pathogens in livestock, food and humans has declined in recent years, according to the latest Integrated Report from the National Antimicrobial Resistance Monitoring System (NARMS). In some cases though, resistance or decreased susceptibility to antibiotics has increased or remained stable within populations of food-borne pathogens, demonstrating that the livestock industry still has work to do in addressing the issue of antimicrobial resistance.
NARMS was established in 1996 as a partnership between the FDA, the Centers for Disease Control and Prevention, and the U.S. Department of Agriculture to track antibiotic resistance in foodborne bacteria.
The report combines information from four data sources, including human clinical isolates, cecal (intestinal) isolates from food-producing animals, isolates from processing plants collected as part of Pathogen Reduction/Hazard Analysis Critical Control Point (PR/HACCP) testing and samples from raw retail meats.
With a focus on food-borne bacteria, NARMS screens specifically for non-typhoidal Salmonella, Campylobacter, Escherichia coli and Enterococcus.
The new report contains data from samples collected in 2014, and the authors note that the data do not reflect any effect of new FDA policies, such as Guidance for Industry 213, which removes label indications for performance uses of medically important antimicrobials in feed. That guidance becomes fully implemented in January 2017, along with the new veterinary feed directive (VFD) rules, which provide veterinary oversight for other uses of medicated feeds.
The report shows several positive trends toward reduced prevalence of antibiotic-resistance in pathogens, and reductions in overall prevalence of food-borne pathogens. These include:
The prevalence of Salmonella and Campylobacter in retail poultry has declined to the lowest levels since testing began. The report shows Salmonella prevalence in in chicken at 9.1% and in ground turkey at 5.5%. Back in 2009, Salmonella prevalence in chicken peaked at over 20%, and prevalence in turkey wasn’t far behind. The report shows the prevalence of Campylobacter in retail chicken meat at 33%. While that figure is high, it has declined considerably from 52% reported in 2003.
Campylobacter causes an estimated 1.3 million illnesses and 120 deaths in the United States each year, with poultry a major contributor. Campylobacter jejuni accounts for about 90% of human Campylobacter infections, with Campylobacter coli causing the remaining 10%.
About 80% of human Salmonella isolates remain susceptible to the antibiotics tested in the study. Resistance for three critically important drugs (ceftriaxone, azithromycin, and ciprofloxacin) in human non-typhoidal Salmonella isolates remained below 3 percent.
Ceftriaxone resistance declined among several pathogens from multiple sources, including non-typhoidal Salmonella. In PR/HACCP samples from beef packers, resistant Salmonella dropped to 7.6%, its lowest level since 1999. In 2010, NARMS researchers found ceftriaxone-resistant Salmonella in more than 20% of their packing-plant samples. The report shows a similar trend in Salmonella isolates from chicken, and ceftriaxone-resistant E. coli from retail chicken meat also declined significantly. In humans, the proportion of Salmonella Heidelberg isolates with ceftriaxone resistance declined to 8.5% from a peak of 24% in 2010 and 15% in 2013.
Multi-drug resistance in human Salmonella isolates has declined for several years in NARMS testing. In the latest report, the percentage of human isolates resistant to at least ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracyclines (ACSSuT) dropped to 3.1%, compared with 8.7% when testing began in 1996.
In cattle, Salmonella typhimurium isolates with ACSSuT resistance declined sharply from 67 percent in 2009 to 7 percent in 2014, the lowest level since this testing began in 1997.
With the exception of five isolates in the past ten years, no resistance has been detected in Enterococcus bacteria isolates to three important drugs: daptomycin, linezolid, and vancomycin.
Not all the news in the latest NARMS report is positive, as some trends in antimicrobial resistance continue to move in the wrong direction. These include:
NARMS researchers have seen an increase in Salmonella serotype Dublin isolates with decreased susceptibility to ciprofloxacin (DSC). Since 2004, 9% of Dublin isolates from humans and 12% from cattle have displayed DSC. Among Dublin isolates with DSC, 57% from humans and 40% from cattle also were ceftriaxone-resistant. Human infections with the Dublin serotype are uncommon but can be severe, and it is one of the most common serotypes found in beef sampling.
The report also notes high and increasing levels of ciprofloxacin resistance in Campylobacter jejuni with 26.7% of isolates from humans and 28% of isolates from chicken PR/HACCP samples showing resistance. Also, more than 35% of Campylobacter coli isolates from humans show resistance to ciprofloxacin.
Read the full 2014 NARMS report online.