FDA: Salmonella, antibiotic resistance declining in US poultry meat
Incidence of Salmonella in ground chicken and turkey meat has dropped to its lowest level since the FDA began monitoring the foodborne pathogen, according to a new report.
However, the development of antibiotic resistance in these foodborne bacteria revealed by the report reflects a more mixed picture, indicating that there is still more to learn on this complex topic.
The FDA report, titled “2014-2015 Retail Meat Interim Report”, includes data on the proportion of samples of raw meat and poultry that tested positive for Salmonella and their level of resistance to antibiotics commonly used in human and veterinary medicine.
Data were collected on samples of grocery-store chicken, ground turkey, ground beef and pork chops obtained between January 2014 and June 2015 and subjected to the National Antimicrobial Resistance Monitoring System (NARMS). This report focuses only on Salmonella, a major pathogen of concern in foodborne disease outbreaks. Information includes serotype distribution, prevalence by food source and state, selected resistance patterns, and a list of all the identified antimicrobial resistance genes.
In ground turkey, the prevalence of Salmonella declined from a high of 19% in 2008 to 6% in 2014 and from 15% to 9% in retail chicken over the same period. The latest figures are the lowest since testing began in 2002.
Salmonella resistance to one particularly important antibiotic, ceftriaxone, from chicken meat continued to decline steadily from a high of 38% in retail chicken meats in 2009 to 18% in 2014, and 5% during the first half of 2015.
For ground turkey, ceftriaxone resistance was detected in 7% of 2014 isolates and 4% of 2015 isolates collected through June, which represents an 80% decline since 2011 when resistance peaked at 22%. Ceftriaxone is a medically important antibiotic used to treat seriously ill patients.
Another critically important group of antibiotics for the treatment of Salmonella infections are the fluoroquinolones, which include ciprofloxacin. Ciprofloxacin resistance was absent in Salmonella from poultry and beef although a single isolate was found in pork.
All Salmonella from retail meats tested were susceptible to azithromycin, another important antibiotic recommended for the treatment of Salmonella and other intestinal pathogens.
Multidrug resistance in Salmonella continued to show a downward drift in chicken and turkey from 2011 levels of 45% and 50%, respectively, to 20% and 36% in June 2015. Under NARMS, the term “multidrug resistance” is given to a pathogen showing resistance to three or more classes of antibiotics, which would restrict the choice of drugs available to treat ill patients.
Area of concern
For the first time, an important resistance gene was detected in Salmonella in chicken in the US. It was only in one sample but it belongs to an important class of resistance genes — extended-spectrum β-lactamase (ESBL) gene – which confer resistance to β-lactam antibiotics, including third-generation cephalosporins, resulting in fewer treatment options for infected patients.
As for the other meats tested, FDA identified the first instance of ciprofloxacin resistance in an isolate from retail pork. Just three isolates of Salmonella serotype Dublin were recovered – all in ground beef – but they exhibited extensive resistance patterns as in the past.
Also for the first time in this series of NARMS reports, FDA has included data from Whole Genome Sequencing (WGS). According to the FDA, WGS has ushered in a new age in infectious-disease science, with the power to greatly enhance diagnosis, tracking and treatment. It has become an inexpensive and rapid tool for characterizing bacteria, offering the opportunity to replace a number of long-standing laboratory methods to identify bacterial species and subtypes, each of which requires specialized training and separate lab processes.
This report includes WGS data for all 271 retail meat isolates from 2014 and 114 Salmonella isolated in the first half of 2015. These data can be used to predict antimicrobial resistance for a number of bacteria, including the foodborne pathogens Salmonella, Campylobacter and E. coli. WGS data also reveal the range of genes causing resistance to a particular antibiotic.
NARMS was established in 1996 as a partnership between the FDA, the Centers for Disease Control and Prevention, and USDA to track antibiotic resistance in foodborne bacteria for drugs that are considered important in human medicine. NARMS is critically important for monitoring trends in antimicrobial resistance among foodborne bacteria collected from humans, retail meats and food animals.
Click on this link to download the 2014-2015 Retail Meat Interim Report.