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United States Department of Agriculture

Agricultural Research Service


Location: Bacterial Epidemiology and Antimicrobial Resistance

Title: A Comparison of Antimicrobial Susceptibility and MIC-distributions in Enterococcus Isolates Originating from Humans, Animals and Retail Meat

item Sjolund, Maria - CDC
item Whichard, Jean - CDC
item Joyce, Kevin - CDC
item Howie, Rebecca - CDC
item Krueger, Amy - CDC
item Barzilay, Ezra - CDC
item Mcdermott, Patrick - FDA
item Hall-Robinson, Elvira - FDA
item Jackson, Charlene
item Cray, Paula

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 28, 2008
Publication Date: April 18, 2008
Citation: Sjolund, M., Whichard, J.M., Joyce, K., Howie, R., Krueger, A., Barzilay, E., Mcdermott, P., Hall-Robinson, E., Jackson, C.R., Cray, P.J. 2008. A Comparison of Antimicrobial Susceptibility and MIC-distributions in Enterococcus Isolates Originating from Humans, Animals and Retail Meat. European Congress of Clinical Microbiology and Infectious Disease. April 19-22, 2008. Barcelona, Spain.

Technical Abstract: Objectives: The National Antimicrobial Resistance Monitoring System (NARMS) is a collaborative effort between the Food and Drug Administration's Center for Veterinary Medicine (FDA CVM), U.S. Department of Agriculture (USDA), and the Centers for Disease Control and Prevention (CDC). The NARMS program monitors resistance among zoonotic pathogenic (Salmonella and Campylobacter) and commensal (E. coli and Enterococcus) bacteria recovered from food animal, retail meat and human sources. Enterococcal data from the NARMS program has however, yet to be compared among these sources. In this study, we report on antimicrobial susceptibility and MIC-distributions of Enterococcus isolates recovered from humans, chickens at slaughter and retail meat. Methods: The first 100 consecutive isolates of E. faecium and E. faecalis from each source submitted in 2005 were included. Minimum inhibitory concentrations (MIC) for 12 antimicrobial agents were determined using broth microdilution methods and interpreted according to CLSI standards, where available. MIC-histograms were constructed and compared with wild type distributions proposed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) ( For each distribution, the MIC50 was calculated. Results: There was good agreement among MIC-distributions of human, chicken and retail meat isolates. For most antimicrobial agents, the MIC50 of the three distributions agreed or was within one dilution step. The most pronounced difference was observed for E. faecium and tetracycline. The MIC50 of human E. faecium isolates was <=4 mg/L whereas the MIC50 for both the chicken and retail meat isolates was 32 mg/L. MIC-distributions of susceptible isolates from all three U.S. sample sources correlated well with the wild type distributions proposed by EUCAST. Conclusion: The MIC50 for all tested antimicrobial agents were similar for all enterococcal isolates, regardless of origin, with the exception of tetracycline where the MIC50 was higher for chicken and retail meat isolates. Additionally, MIC-distributions of susceptible enterococci from all three U.S. sample sources agreed well with the wild type distributions defined by EUCAST. This implies that the enterococcal wild type distributions are similar regardless of geographic origin and sample source.

Last Modified: 9/23/2014
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