FDA cites mixed findings on resistance in foodborne bacteria

Jul 26, 2012 (CIDRAP News) – A US government report released this week on the prevalence of antimicrobial resistance in major foodborne pathogens paints a mixed picture, with some markers down or stable but others in double digits or increasing.

The report from the Food and Drug Administration (FDA) mainly presents 2010 findings from the National Antimicrobial Resistance Monitoring System (NARMS) on Salmonella and Campylobacter in humans, retail meat, and animals at slaughter. It also includes some data on Escherichia coli in retail meat and chicken carcasses.

NARMS is a joint project of the FDA, the Centers for Disease Control and Prevention, the US Department of Agriculture, and a number of state health departments.

Some of the findings in the report, titled NARMS 2010 Executive Report, were presented in March in a document that covered only retail meat samples.

Salmonella findings
The report summary says 3,947 non-typhoidal Salmonella isolates were tested in 2010, including 2,474 from humans, 400 from retail meats, and 1,073 from food animals at slaughter. In retail meat sampling, Salmonella was found in 15% of ground turkey samples, 13% of chicken breasts, 1.5% of pork chops, and 0.5% of ground beef.

In a breakdown of Salmonella serotypes, the report notes that Salmonella Dublin, which is associated with invasive salmonellosis in humans, made up 17% of Salmonella isolates in slaughter cattle. It was the second most common serotype after Montevideo and has increased steadily since 1997.

A positive finding was that resistance to nalidixic acid—a marker for resistance to fluoroquinolones, which are important in treating complicated salmonellosis cases—has remained below 3% in all types of samples since 2004. Resistance to the drug was found in 2.8% of cattle isolates and less than 1% of turkey isolates.

On the less-bright side, NARMS found considerable resistance to ceftriaxone, another drug that's important for treating complicated Salmonella infections. Resistance to the drug was found in 35% of retail chicken breast isolates, which is down from 38% in 2009 but well above the 16% reported for 2007.

In retail ground turkey Salmonella isolates, ceftriaxone resistance increased from 5.7% in 2009 to 16% in 2010, which is the highest since testing began in 2002, the report says.

For the animal findings, ceftriaxone resistance was at 22% in cattle isolates, 15% in turkey isolates, 12% in chicken isolates, and 1.8% in swine. The resistance levels in the cattle and turkey samples were the highest since testing began in 1997.

On the other hand, 85% of the human Salmonella isolates tested showed no resistance to any of the antimicrobials tested, which was an increase from 74% in 1999. For the other types of samples, the proportion of isolates showing no resistance ranged from 61% for cattle and 57% in ground beef to 25% in turkeys and 31% in retail ground turkey.

NARMS investigators also tallied Salmonella with multidrug resistance, defined as resistance to three or more antimicrobial classes. They found that multidrug resistance in human isolates was at 9.1%, the lowest since 1996, but it increased in some serotypes.

Among chicken breast isolates, multidrug resistance declined from 49% in 2009 to 43% in 2010, after rising the preceding 3 years. Multidrug resistance was found in 34% of ground turkey isolates, down from a peak of 52% in 2008, but in slaughter turkeys, such resistance was 37%, up from 30% in 2008.

Also, multidrug resistance in specimens from slaughter cattle increased from 22% in 2007 to 28% in 2010, the report says.

Campylobacter results
NARMS officials tested 2,136 Campylobacter isolates, including 1,310 from humans, 518 from retail meats (505 from chicken breasts and 13 from ground turkey), and 308 from chickens at slaughter. Investigators looked at both C jejuni and C coli; C jejuni was more common in all types of samples.

Resistance to important antimicrobial classes was mostly higher among C coli than among C jejuni isolates in all the sample types, the report says.

On the positive side, investigators found only low levels of Campylobacter resistance to erythromycin, an important drug for treating severe Campylobcter infections in humans. In C jejuni from humans, chicken breasts, and chickens, resistance to the drug has stayed below 4.0% since testing began. C coli resistance to the drug was only slightly above 4.0%.

However, ciprofloxacin resistance among C jejuni from humans, chicken breasts, and chickens was above 20%. The drug, a fluoroquinolone, is an alternative therapy for Campylobacter infections in humans, the report says. It notes that the FDA withdrew approval for the two poultry fluoroquinolones, sarafloxacin and enrofloxacin, in 2001 and 2005.

On the other hand, gentamicin resistance among C jejuni from humans, chicken breasts, and chickens was less than 1%. The report describes gentamicin as a highly important drug for treating severe infections from food animal sources, including campylobacteriosis. Gentamicin is also used in chickens, including to protect day-old chicks from lethal infections.

See also:

Jul 23 FDA press release

NARMS report home page

NARMS report summary

March 5 CIDRAP News story on NARMS retail meat report for 2010

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