Mar 5, 2012 (CIDRAP News) – A new US government report shows that the prevalence of antibiotic-resistant bacteria in retail poultry and meat samples in 2010 varied greatly depending on the type of bacteria and meat, with resistant Salmonella in chicken breasts one of the more common findings.
The 2010 retail meat report of the National Antimicrobial Resistance Monitoring System (NARMS), released Mar 1, also suggests that the 2005 ban on use of fluoroquinolones in poultry is helping to reduce the prevalence of resistance to some of those drugs.
The NARMS retail meat surveillance program is a joint effort of the US Food and Drug Administration (FDA), the Centers for Disease Control and Prevention, and the health departments of 11 states: California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, Tennessee, and Pennsylvania. Its goals include providing information to promote steps to reduce resistance among foodborne bacteria.
The 2010 findings are based on tests of 5,280 samples, the report says. Each state bought about 40 samples each month, with 10 each of chicken breasts, 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. In 2010, 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 confirmation of the species and serotypes, antimicrobial susceptibility testing, and genetic analysis, the report says.
The document shows that in 2010 Salmonella (including susceptible and resistant strains) was found on 13% of chicken breasts, 15.3% of ground turkey samples, 0.5% of ground beef, and 1.5% of pork chops. Campylobacter was found on 38.3% of chicken breasts and 1.0% of ground turkey.
Enterococcus isolates (both susceptible and resistant) were very common, found on 95.4% of chicken breasts, 90.7% of ground turkey, 90.2% of ground beef, and 88.3% of pork chops. The numbers were somewhat lower for E coli: chicken breasts, 77.6%; ground turkey, 80.2%; ground beef, 58.5%; and pork chops, 39.8%.
Enterococcus species and E coli normally live harmlessly in the human gut, but they can cause infections in other parts of the body, such as the urinary tract, and certain E coli strains, such as O157:H7, cause serious gastrointestinal disease.
The complex report consists mainly of numerous tables showing resistance data by bacteria type, sample type, and antibiotic class.
For Salmonella, the report shows significant growth in resistance to third-generation cephalosporins between 2002 and 2010 in chicken breasts (from 10% to 34.5% of isolates) and ground turkey (from 8.1% to 16.3%). Significant increases were also seen in ampicillin-resistant Salmonella isolates in chicken breasts (16.7% to 39.2%) and ground turkey (16.2% to 48%) over that same period.
The report also shows that a sizeable share of the Salmonella isolates in poultry products were resistant to more than one antibiotic: 43.3% of chicken-breast isolates and 33.7% of ground turkey were resistant to at least three antimicrobial classes. Further, more than 29% of chicken breast isolates showed resistance to five or more classes of drugs.
"[Salmonella] serotype Albert was isolated from ground turkey for the first time since 2002 and was resistant to all 8 classes of antimicrobials tested," the report adds.
On the other hand, Salmonella strains that were susceptible to all antibiotics increased from 2009 to 2010 in turkey breasts (from 29% to 35.7%) and ground turkey (22.3% to 30.7%). But such "pansusceptible" Salmonella isolates decreased in pork chops, from 50% to 35%.
More than 90% of Campylobacter isolates identified in the NARMS program come from chicken breasts, the report says. About two thirds of these are C jejuni, and the rest are C coli, which tends to be more resistant than C jejuni.
Chicken-breast C coli resistance to ciprofloxacin, a fluoroquinoline, peaked at 29.1% in 2005, when the FDA banned fluoroquinoline use in poultry, the report says. Since then, C coli resistance to ciprofloxacin has declined, dropping to 13.5% in 2010. However, the report notes no parallel drop in C jejuni resistance to ciprofloxacin, which rose from 15.2% in 2002 to 22.5% in 2010.
Some signs of effects of the fluoroquinolone ban have also been seen in the E coli category. Resistance to nalidixic acid, a marker for fluoroquinolone resistance, increased from 2002 to 2005 in chicken breast E coli isolates (2.8% to 6.6%) and ground turkey isolates (4.3% to 10.4%). But since the ban in 2005, resistance has dropped to 3.6% in chicken breasts and 2.7% in ground turkey.
In other E coli findings, ampicillin resistance in ground turkey isolates reached 52.6% in 2010, compared with 31.3% in 2002. Gentamicin resistance was much higher in poultry samples (over 20%) than in ground beef and pork chop isolates (less than 5%).
In other Campylobacter results, tetracycline resistance in C jejuni dropped from 45.8% to 36.3% between 2009 and 2010, while such resistance in C coli stayed the same at 39.2%, the report says. But gentamicin resistance in C coli reached 12.8% in 2010, up from 0.7% in 2007.
Multidrug resistance was rare in Campylobacter, with only 9 of 555 isolates resistant to three or more antimicrobial classes.
In the Enterococcus category, the report says streptogramin resistance has significantly dropped since 2002 in chicken breasts (from 56.3% to 27.1% of isolates), ground beef (26.2% to 2.3%) and pork chops (27.2% to 3.8%) but has remained above 50% in turkey samples. Resistant Enterococcus species are used as sentinels for antibiotic selection pressures from drugs active against gram-positive bacteria, which are used in both food animals and humans, the document says
2010 NARMS retail meat report homepage
NARMS report highlights
General information on NARMS
Mar 1 FDA news release on the report