Student Research: Anika Larson

, Environmental and Occupational Health (EOH), 2017
Faculty Advisor: Peter Rabinowitz

3rd-Generation Cephalosporin Resistance in Retail Meat from the U.S. National Antimicrobial Resistance Monitoring System (NARMS)


Abstract

Non-typhoidal Salmonella is estimated to be the leading cause of death and hospitalization among foodborne pathogens in the United States. In 2012, the FDA implemented an Order of Prohibition that prohibited certain extra-label uses of third-generation cephalosporin antibiotics in major food-producing animals (FDA, 2012). The probability of resistance to ceftriaxone in Salmonella enterica isolates in retail meat from the National Antimicrobial Resistance Monitoring System (NARMS) was modeled as a function of time and location using a generalized additive mixed effects model. There was a statistically significant (p<0.01) association between ceftriaxone resistance and a fitted smooth function for time, and a decline in the probability of ceftriaxone resistance was observed following the 2012 Order of Prohibition. This observation is consistent with the hypothesis that the Order of Prohibition reduced selection pressure for extended-cephalosporin resistance in Salmonella enterica populations in food animals; however, the decline in resistance was largely attributable to changes in serovar prevalence over time. Subtype analyses of serovars Heidelberg and Typhimurium found a statistically significant (p<0.05) association between ceftriaxone resistance and a fitted smooth function for time for the Heidelberg serovar, where a decline in the probability of ceftriaxone resistance was observed following the 2012 Order of Prohibition, but the association between ceftriaxone resistance and time was not significant in serovar Typhimurium. Future analyses should examine genetic data available for later years of the NARMS retail meat dataset to examine whether genetic analysis is consistent with differences in genetic mechanisms of resistance by Salmonella serovar.