FDA cautions interpretation of antimicrobial resistance data

Published on: Apr 22, 2013

The Food & Drug Administration issued a statement April 22 cautioning the interpretation of antimicrobial resistance data after the Environmental Working Group (EWG) recently issued a report of its interpretation of the 2011 Retail Meat Annual Report of the National Antimicrobial Resistance Monitoring System (NARMS).

While FDA is always concerned when it sees antimicrobial resistance, the agency said it believes the EWG report oversimplifies the NARMS data and provides misleading conclusions. FDA said it does not believe that EWG fully considered important factors that put these results in context, including:

* Whether the bacterium is a foodborne pathogen. The report highlights resistance to Enterococcus, but this is not considered a foodborne pathogen. Instead, FDA includes it because its behavior is helpful in understanding how resistance occurs.

* Which drug(s) the bacterium is naturally resistant to. For example, most Enterococcus faecalis is naturally resistant to the antibiotic class of lincosamides. Because this resistance is known and expected, FDA is not as concerned with resistance in this species the way it would be with resistance in true pathogens like Salmonella and Campylobacter.

* Why NARMS includes certain drugs in its testing design. Some antibiotics for are included epidemiology purposes — to track the spread of certain bacteria or certain genes. However, resistance to these antibiotics doesn't reflect a danger to public health.

* Whether the antibiotics that are commonly used to treat patients are still effective. NARMS data indicates that first-line treatments for all four bacteria that are tracked (Salmonella, Enterococcus, Escherichia coli and Campylobacter) are still effective.

* What the 2011 data indicate relative to similar data reported for prior years.

Additionally, FDA said it believes that it is inaccurate and alarmist to define bacteria resistant to one, or even a few, antimicrobials as "superbugs" if these same bacteria are still treatable by other commonly used antibiotics. This is especially misleading when speaking of bacteria that do not cause foodborne disease and have natural resistances, such as Enterococcus.

When taking such factors into account, FDA believes the notable findings in the 2011 NARMS Report include:

* In the critically important class of antimicrobials, the 2011 data showed no fluoroquinolone resistance in Salmonella from any source. This is the drug of choice for treating adults with Salmonella.

* Fluoroquinolone resistance in Campylobacter has stopped increasing and remained essentially unchanged since FDA withdrew the use of this drug class in poultry in 2005. Trimethoprim-sulfonamide is another drug used to treat Salmonella infections and resistance remains low (0-3.7%).

* Macrolide antibiotic resistance in retail chicken isolates remains low, with 2011 results at 0.5% of Campylobacter jejuni and 4.3% of Campylobacter coli. The macrolide antibiotic erythromycin is the drug of choice for treating Campylobacter infections.

* Multidrug resistance is rare in Campylobacter. Only nine out of 634 Campylobacter isolates from poultry were resistant to three or more antimicrobial classes in 2011. However, gentamicin resistance in Campylobacter coli markedly increased from 0.7% in 2007 (when it first appeared in the NARMS retail meat report) to 18.1% in 2011. Gentamicin has been suggested as a possible second-line therapy for Campylobacter infections, although it is not commonly used.

* Resistance to third-generation cephalosporins, which are used to treat salmonellosis, has increased in Salmonella from chicken (from 10% to 33.5%) and turkey (from 8.1% to 22.4%) meats when comparing 2002 and 2011 percentages. FDA noted this development in previous years and has already taken action by prohibiting certain extra-label uses of cephalosporins in cows, pigs, chickens and turkeys, and is continuing to closely monitor resistance to these drugs.

FDA reiterated that antimicrobial resistance is a serious and challenging issue, and noted that it is critically important that efforts are continued to minimize antimicrobial resistance, including promoting appropriate and judicious use of antimicrobials in both humans and animals.

More details on FDA's statement can be found at www.fda.gov/AnimalVeterinary/NewsEvents/CVMUpdates/ucm348794.htm?source=govdelivery.