An annual federal report released this week on drug resistance in bacterial foodborne illness culprits mainly showed encouraging patterns but raised concerns about multidrug resistance in two Salmonella serotypes.
The findings are from the National Antimicrobial Resistance Monitoring System (NARMS), a collaboration of three federal agencies that between them track resistant bacteria in humans, retail meat, and food animals. The respective agencies include the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), and the US Department of Agriculture (USDA).
The report focuses on foodborne pathogens that resist antibiotics considered crucial to human medicine and on multidrug resistant bacteria—those that resist agents in three or more antibiotic classes. The system screens for nontyphoidal Salmonella, Campylobacter, Escherichia coli, and Enterococcus; Salmonella and Campylobacter are the leading bacterial causes of foodborne illness.
Methodology and testing changes
This year's report for the first time covers multiple years, 2012 and 2013, and has a new format that includes 10 interactive graphs to help show resistance patterns in Salmonella and Campylobacter in humans, retail foods, and animals through 2013, the FDA said in a press release yesterday. It added that the report also reflects improvements in NARMS testing. For example, animal testing now includes cecal (intestinal) testing of food-producing animals before slaughter, which may provide a more accurate picture of animals' microbial status in farm settings.
Also, the FDA said it is using epidemiologic cut-off values that move toward global harmonization of Campylobacter surveillance methods as well as updating measurements for cefepime in response to changes made to best practices for international testing. Cefepime is an antibiotic used to screen for extended-spectrum beta-lactamase (ESBL) production, a mechanism linked to drug resistance.
In encouraging findings, the NARMS study found that overall, Salmonella isolates are holding the line against resistance. About 80% of human Salmonella isolates aren't resistant to any tested antibiotics, a number that hasn't changed over the past decade. Resistance to the three most important drugs used to treat human Salmonella isolates—ceftriaxone, azithromycin, and quinolones—remains below 3%.
Similarly, Salmonella multidrug resistance in human, cattle, and chicken isolates hasn't changed in the last 10 years, remaining at about 10%. Also, the number of multidrug-drug resistant Salmonella isolates in retail chicken has decreased to around 3%, according to the report.
For Campylobacter jejuni, the subtype that causes most human campylobacteriosis cases, resistance to ciprofloxacin, the drug most commonly used for treatment, declined to its lowest level in retail chicken to date (11%).
Among the worrisome findings, multidrug resistance in human isolates of the common Salmonella serotype l 4,,12:i:- is still rising, and has doubled from 18% in 2011 to 46% in 2013, according to the FDA.
The report also pointed to another concern, an increase in multidrug resistance and ceftriaxone resistance in Salmonella Dublin subtypes isolated from cattle and humans.
Aug 11 FDA press release
2012-2013 NARMS report homepage
Jul 20, 2014, CIDRAP News story "Resistant foodborne bacteria: good news, bad news in 2012"