Bacteria in meat show growing drug resistance, FDA says

Feb 7, 2013 (CIDRAP News) – An annual report released by the Food and Drug Administration (FDA) this week shows that antibiotic resistance in bacteria found in retail meat and poultry samples is continuing to increase, though not uniformly.

For example, almost 45% of Salmonella isolates found on retail chicken samples were resistant to multiple classes of antimicrobial classes, up slightly from the 2010 level, says the 2011 Retail Meat Report of the National Antimicrobial Monitoring System (NARMS). Also, close to half of Campylobacter isolates in chicken were resistant to tetracyclines.

The report also shows that Campylobacter contamination in general (both susceptible and resistant isolates) increased in chicken and ground turkey samples in 2011, while Salmonella detections were down slightly for both items.

The NARMS retail meat surveillance program is a joint effort of the FDA, the Centers for Disease Control and Prevention (CDC), and health departments in 11 states: California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, Tennessee, and Pennsylvania. Its goals include providing information to promote steps for reducing resistance in foodborne bacteria.

In 2011, each health department bought about 40 retail samples each month—10 each of chicken, ground turkey, ground beef, and pork chops. All the state labs cultured meat and poultry samples for Salmonella, but only poultry samples were cultured for Campylobacter. Four of the states also cultured samples for Enterococcus and Escherichia coli.

The states sent their bacterial isolates to the FDA Center for Veterinary Medicine for identification of serotypes, antimicrobial susceptibility testing, and genetic analysis, the report says.

Resistant Salmonella
The testing revealed that 44.9% of Salmonella isolates in chicken were resistant to at least three antimicrobial classes in 2011, compared with 43.3% in 2010. In ground turkey, 50.3% of isolates showed this level of resistance, up from 33.7% the year before. In addition, 27% of chicken isolates showed resistance to at least five drug classes, which was down from 29% in 2010.

The report also says the percentage of Salmonella isolates with no detected resistance declined in 2011.

The researchers found continuing increases in Salmonella resistance to two specific drug classes. Between 2002 and 2011, resistance to third-generation cephalosporins in chicken isolates climbed from 10% to 33.5%, while such resistance in ground turkey rose from 8.1% to 22.4%. Both increases were significant (P <.05).

Significant increases over that same period were seen for Salmonella resistance to ampicillin: chicken isolates, 16.7% to 40.5%; ground turkey isolates, 16.2% to 58.4%.

On the other hand, all Salmonella isolates were susceptible to nalidixic acid, a member of the quinolone class, the report says.

Campylobacter resistance
More than 90% of Campylobacter isolates come from chicken samples each year, with the rest from ground turkey, the report notes. It says macrolide and fluoroquinolone drugs are used to treat Campylobacter infections. Fluoroquinolone use in poultry production was banned in 2005.

Macrolide resistance in chicken samples remained low in 2011, at 4.3% for Campylobacter coli and 0.5% for Campylobacter jejuni, the testing showed.

C coli resistance to ciprofloxacin, a fluoroquinolone, peaked at 29.1% in 2005 and has dropped since then, reaching 18.1% in 2011, the report says. However, C jejuni resistance to the drug has continued an upward trend, from 15.2% in 2002 to 22.4% in 2011.

In addition, tetracycline resistance in both Campylobacter species jumped from 2010 to 2011, from 36.3% to 48.4% for C jejuni and from 39.2% to 29.1% for C coli.

Further, gentamicin resistance in C coli reached 18.1% in 2011, a big increase from the 0.7% level seen in 2007 when it was first detected.

On the brighter side, the report says multidrug resistance is rare in Campylobacter: Only 9 of 634 isolates from poultry were resistant to three or more drug classes in 2011.

The report also profiles resistance in Enterococcus species and Escherichia coli found in meat and poultry samples. Among other things, it notes that no Enterococcus isolates were resistant to vancomycin or linezolid, two drug classes that "are critically important in human medicine but are not used in food animal production."

General prevalence
As for the overall prevalence of contamination (susceptible and resistant strains), the project showed that 45.7% of chicken samples in 2011 contained Campylobacter, up from 38.3% in 2010. For ground turkey, the 2011 figure was 2.3%, up from 1.0% in 2010.

For Salmonella, the general prevalence in chicken was 12.0%, down from 13.0% the year before, while the ground turkey figure was 12.3%, down from 15.3% a year earlier. Salmonella was found in less than 1% of ground beef samples both years. For pork chops, the 2011 number was 2.1%, up from 1.5% in 2010.

For E coli (most strains of which are nonpathogenic), prevalence numbers were lower in 2011 than 2010 but remained fairly high: chicken, 71.0%; ground turkey, 76.7%; ground beef, 44.8%; and pork chops, 30.4%.

Congress member reacts
Rep. Louise Slaughter, D-N.Y., a food safety advocate, called the FDA's findings on resistance in meat samples "alarming." In a statement, she cited the high level of ampicillin resistance found in bacteria in ground turkey and the tetracycline resistance seen in Campylobacter from poultry samples.

"The threat of antibiotic-resistant disease is real, it is growing and those most at risk are our seniors and children," Slaughter said. "We can help stop this threat by drastically reducing the overuse of antibiotics in our food supply, and Congress should act swiftly to do so today."

See also:

Feb 5 FDA announcement about NARMS report

NARMS report highlights

NARMS report homepage

Full NARMS report

2012 NARMS story

Louise Slaughter press release

Mar 5, 2012, CIDRAP News story "Report cites mixed data on resistant bacteria in poultry, meat"

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