FDA report finds resistant Salmonella down in meat

Meat at market
Meat at market

UGA College of Agriculture & Environmental Sciences / April Sorrow

It its annual reporting on antibiotic resistance in Salmonella found in US retail poultry and meat, the Food and Drug Administration (FDA) said resistant strains are down but also noted worrisome findings, such as the country's first detection of a certain class of resistance gene.

The report focuses only on antimicrobial resistance in Salmonella from raw retail poultry and meat samples collected through the National Antimicrobial Resistance Monitoring System (NARMS), a partnership with the Centers for Disease Control and Prevention and the US Department of Agriculture to monitor antibiotic resistance in foodborne bacteria for drugs that are crucial for human health.

Among new developments with NARMS reporting, the FDA said it will issue its interim meat reports twice a year to make them timelier. The FDA's latest report covers data from January 2014 though June 2015. Also, for the first time the report includes whole-genome sequencing (WGS) for the Salmonella isolates.

Lowest levels since testing began

The FDA said the data reflect improvements since 2011 on several fronts. For example, Salmonella prevalence in retail poultry sank to its lowest level since testing began in 2002. Detections in ground turkey dropped from a high of 19% in 2008 to 6% in 2014, and, over the same period, positive results in retail chicken fell from 15% to 9%.

When the FDA looked at resistance to ceftriaxone, an antibiotic used for treating seriously ill patients, in Salmonella from retail chicken investigators noted a steady decline, from a high of 38% in 2009 to 18% in 2014, with a further decline to 5% for the first half of 2015. In ground turkey, ceftriaxone resistance was found in 7% of Salmonella samples in 2014, with the level declining to 4% for the first half of 2015, progress that reflects an 80% decline from the 2011 peak of 22%.

Resistance to ciprofloxacin, a fluoroquinolone critical for treating Salmonella infections, was detected in only one sample—from pork. All of the Salmonella isolates from retail meat were susceptible to azithromycin, another antibiotic vital for treating Salmonella illness and other intestinal pathogens.

Multidrug Salmonella resistance continued to drop in chicken and turkey from 2011 levels of 45% and 50%, respectively, to 20% and 36% in June 2015.

Causes for concern

The worrisome findings were fewer but included a ceftriaxone-resistant chicken isolate from 2014 that had the extended-spectrum beta-lactamase (ESBL) gene blaCTX-M6-5, the first such detection in the United States.

Though testing turned up only three Salmonella serotype Dublin isolates in 2014, they were extensively resistant, as seen in the past. The samples showed resistance to 9 to 12 of 14 drugs tested.

Whole-genome sequencing adds detail

With WGS now an inexpensive and rapid tool for characterizing bacteria, NARMS scientists can use it to predict antimicrobial resistance for several bacteria and identify the genes that cause resistance to a specific antibiotic, the FDA said. The new report includes WGS data for all 271 retail meat isolates from 2014 and for 114 Salmonella isolates from the first half of 2015.

The WBS analysis found antibiotic-resistant genes in different quinolone resistance mechanisms, including the first known identification in US retail meat of a plasmid-mediated qnrS gene from a single ciprofloxacin-resistant isolate from pork.

"Despite these findings, Salmonella largely remained susceptible to ciprofloxacin and other first line human clinical therapies, including azithromycin, during 2014 and the first half of 2015," the FDA said.

See also:

Apr 28 FDA press release

Apr 15, 2015, CIDRAP News scan "US offers mixed news on drug resistance in foodborne pathogens"

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