Drug resistance rises among some Salmonella serotypes

While the overall rate of antibiotic-resistant foodborne germs remained stable since 2011, resistance in some serotypes of Salmonella have increased significantly, according to 2013 surveillance data from the National Antimicrobial Resistance Monitoring System.

NARMS — a collaborative effort by state and local health departments, the CDC, FDA and the Agriculture Department — is dedicated to monitoring changes in antibiotic resistance in six common foodborne germs isolated from retail meats, livestock and ill individuals. In 2013, NARMS evaluated more than 5,000 germs from humans for antibiotic resistance, assessing them for changes from the previous years’ data.

It conducted surveillance across the United States for: Salmonella (typhoidal and nontyphoidal), Shigella, Escherichia coli and species of Vibrio other than V. cholerae. In addition, surveillance of Campylobacter was conducted in 10 states represented in the Foodborne Disease Active Surveillance Network. NARMS specifically evaluated these germs for multidrug resistance, which is characterized by resistance to three or more classes of antibiotics.

It found that while resistant Salmonella has remained consistent, some serotypes of the bacteria have become increasingly resistant. In 2013, a common serotype of Salmonella (I4,[5],12:i:-) had a 46% rate of multidrug resistance, which was more than twofold the rate observed in 2011. This serotype also was found to have increasing resistance (from 18%) to ampicillin, streptomycin, sulfonamides and tetracycline. This increase is thought to be attributable to clonal expansion, according to the report.

Campylobacter isolated from ill individuals also was tested, with about one in four samples found to be resistant to quinolones such as ciprofloxacin. Additionally, 2% of Campylobacter isolates were resistant to erythromycin, and 18% were resistant to azithromycin.

For Shigella, the researchers found that 3% of the samples were resistant to ciprofloxacin, 5% were resistant to nalidixic acid, and 4% were resistant to azithromycin.

According to the NARMS report, steps are in place to decrease the excessive use of antibiotics in animals and people. Moreover, the Obama administration’s fiscal year 2016 budget seeks additional CDC funding to more closely monitor drug-resistant Salmonella and other resistant germs.

“The proposed initiative would allow CDC to check nearly every Salmonella sample and many more Campylobacter samples for resistance more quickly,” NARMS said in a media advisory. – by Jen Byrne

Reference:

CDC. National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS): Human Isolates Final Report, 2013. Department of Health and Human Services, CDC, 2015.

Disclosure: The researchers report no relevant financial disclosures.