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United States Department of Agriculture

Agricultural Research Service

Title: Factors Affecting the Testing for Antimicrobial Resistance

Authors
item Cray, Paula
item Englen, Mark
item Gray, Jeffrey
item Jackson, Charlene
item Headrick, Marcia - FDA-CVMA
item Tollefson, Linda - FDA-CVM
item Anandaraman, Neena - USDA-FSIS
item Salamone, Bernard - USDA-FSIS
item Rose, Bonnie - USDA-FSIS
item Dargatz, David - USDA-APHIS

Submitted to: American Veterinary Medical Association Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 19, 2003
Publication Date: July 19, 2003
Citation: Cray, P.J., Englen, M.D., Gray, J.T., Jackson, C.R., Headrick, M.L., Tollefson, L., Anandaraman, N., Salamone, B.P., Rose, B.E., Dargatz, D.A. 2003. Factors affecting the testing for antimicrobial resistance. American Veterinary Medical Association Abstract. P. 45.

Interpretive Summary: Diagnostic and research laboratories typically use routine, well established, antimicrobial susceptibility test procedures to determine whether an isolate is susceptible or resistant to a particular antimicrobial. Often, the origin of the isolate is not considered when susceptibility results are analyzed. However, we have determined that bacterial culture, selection, and speciation methods can significantly impact antimicrobial susceptibility results. As part of the animal arm of the National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS), Salmonella, Campylobacter, generic E. coli, and Enterococci isolates are tested for resistance to approximately seventeen antimicrobials which are important in human and veterinary medicine. We have observed that culture methodology impacts the major and minor populations of bacteria present for selection after incubation, particularly if antimicrobials are used in the culture media and/or identification process. Since selection of isolates occurs after culture, use of certain media (in the presence or absence of antimicrobials) may confound the selection process. Speciation of the isolate, or lack thereof, may also confound the analyses and lead to erroneous assumptions. Culture methodology of samples, selection of isolates, speciation of isolates, and susceptibility outcome will be discussed.

Technical Abstract: Diagnostic and research laboratories typically use routine, well established, antimicrobial susceptibility test procedures to determine whether an isolate is susceptible or resistant to a particular antimicrobial. Often, the origin of the isolate is not considered when susceptibility results are analyzed. However, we have determined that bacterial culture, selection, and speciation methods can significantly impact antimicrobial susceptibility results. As part of the animal arm of the National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS), Salmonella, Campylobacter, generic E. coli, and Enterococci isolates are tested for resistance to approximately seventeen antimicrobials which are important in human and veterinary medicine. We have observed that culture methodology impacts the major and minor populations of bacteria present for selection after incubation, particularly if antimicrobials are used in the culture media and/or identification process. Since selection of isolates occurs after culture, use of certain media (in the presence or absence of antimicrobials) may confound the selection process. Speciation of the isolate, or lack thereof, may also confound the analyses and lead to erroneous assumptions. Culture methodology of samples, selection of isolates, speciation of isolates, and susceptibility outcome will be discussed.

Last Modified: 11/26/2014
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