A new federal government report on antibiotic resistance in foodborne pathogens reveals that multidrug resistance in a common Salmonella serotype remains above 40 percent and that this resistance more than doubled between 2011 and 2014. According to the “NARMS 2014 Human Isolates Surveillance Report,” this level of resistance in Salmonella l 4,[5],12:i:- “has been linked to animal exposure and eating pork or beef, including meat purchased from live animal markets.” For the first time, the NARMS (National Antimicrobial Resistance Monitoring System for Enteric Bacteria) annual surveillance report used whole genome sequencing data of bacteria from people with antibiotic-resistant Salmonella infections. The 2014 NARMS report includes the most recent nationwide data on antibiotic resistance commonly transmitted by food, including Salmonella, Shigella, Campylobacter, E. coli O157 and Vibrio species other than Vibrio cholerae. “Bacterial foodborne infections are common and can sometimes be serious. In severe cases, the right antibiotic, also called antimicrobial agent, canbe life-saving,” according to the report. “Some antibiotics don’t work because the foodborne pathogen has become resistant. Understanding trends in antibiotic resistance helps doctors to prescribe effective treatment and public health officials to investigate outbreaks faster.” Trends included in the report were gathered by comparing the prevalence of antibiotic resistance in 2014 with that from 2004-2008 and from the previous five years, 2009-2013.
The 2004-2008 reference period begins with the second year that all 50 states participated in Salmonella and Shigella surveillance and all 10 FoodNet sites participated in NARMS Campylobacter surveillance, the report notes. The additional 2009-2013 reference period allowed comparison with the more recent years.
The NARMS report calls some trends from these data “encouraging,” while others were termed “concerning.” Among the former were findings that multidrug resistance in Salmonella in 2014, which was at 9.3 percent, was similar to 2013, when it was 9 percent. It has “remained stable” over the past 1o years at 11 percent. Resistance to the antibiotic ceftriaxone in Salmonella in 2014 was still rare at 2 percent. It was 3 percent in 2004-2008 and 2009-2013, according to the report. Other “encouraging” findings included:
- Resistance to certain groups of antibiotics in Salmonella Typhimurium and Salmonella Newport remained lower in 2014 compared with 2004-2008.
- No Salmonella isolates had decreased susceptibility to both azithromycin and ciprofloxacin, and none had both decreased susceptibility to azithromycin and resistance to ceftriaxone, which are important drugs for the treatment of severe Salmonella infections.
Findings deemed “concerning” included:
- Six of the 51 ceftriaxone-resistant Salmonella in 2014 had an extended-spectrum β-lactamase (ESBL) gene identified by whole genome sequencing. ESBLs are rare among Salmonella in the U.S. Many of these infections are acquired during international travel.
- Salmonella serotypes Dublin, Heidelberg, Newport and Typhimurium accounted for nearly two-thirds of isolates resistant to ceftriaxone.
- Sixty percent of serotype Dublin isolates were resistant to ceftriaxone.
- Decreased susceptibility to ciprofloxacin in Salmonella was higher in 2014 at 4 percent than in the baseline period of 2004-2008 when it was 2 percent and in 2009–2013 when it was 3 percent.
- Eight percent of Salmonella Enteritidis had decreased susceptibility to ciprofloxacin, accounting for 38 percent of all ciprofloxacin-resistant Salmonella isolates.
- Salmonella Typhi, which causes typhoid fever, also showed higher levels of decreased susceptibility to ciprofloxacin: 2014, 74 percent; 2009-2013, 68 percent; and 2004-2008, 53 percent.
- Campylobacter resistance to fluoroquinolones remained high, at times leaving macrolides as the only treatment option.
- Ciprofloxacin resistance in Campylobacter jejuni, the most common species isolated from humans, increased from 22 percent in 2013 to 27 percent in 2014. Resistance in Campylobacter coli was 35 percent, similar to recent years.
- Macrolide resistance decreased from 18 percent in 2013 to 10 percent in Campylobacter coli in 2014 and remained at 2 percent in Campylobacter jejuni.
- Decreased susceptibility to azithromycin increased among Shigella flexneri from 16 percent in 2013 to 22 percent in 2014.
NARMS is a partnership formed in 1996 between the U.S. Centers for Disease Control and Prevention, the U.S. Food and Drug Administration, the U.S. Department of Agriculture, and state and local health departments. It is the only source of national information on antibiotic resistance in foodborne pathogens in the U.S.
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