Antimicrobial susceptibility testing remains a valuable diagnostic tool for the veterinary practitioner in determining the most effective treatment for bacterial infections. When submitting a specimen for culture and susceptibility testing, it is important to provide treatment history with specific antibiotics previously used, and any clinical history that may affect the patient’s normal bacterial flora.

We have many antibiotics and panels of antibiotics available for diagnostic testing (see below). The panel chosen to be reported will vary depending on the type and growth requirements of the bacterial pathogen isolated, the animal species of origin,. Please mark clearly on the submittal form if requesting a particular antimicrobial agent or testing method.

We follow Clinical Laboratory Standards Institute (CLSI, formerly NCCLS) guidelines for antimicrobial susceptibility testing and reporting of antibiotics based on animal species, when available. The source of data for interpretive guidelines (animal species or human clinical breakpoints) and the resistance breakpoints are listed at

While we try to provide our clients with as much useful information as possible, antimicrobial susceptibility reports are not treatment recommendations. Some of the antimicrobial agents listed in the report may not be approved for use in all classes of animals. Veterinarians/clients assume responsibility for antimicrobial therapy they initiate including choice of appropriate.

Use of Antimicrobial Susceptibility Results

Bacterial Susceptibility Profiles

The Bacteriology Section at the MSU VDL runs thousands of AST panels annually. Cumulative AST data at a particular institution over a defined time period may be summarized to provide guidance in the selection of empirical antimicrobial therapy for infections and is reported as the percentage of organisms susceptible.

Cumulative AST profiles* for bacteria isolated from dog and cat specimens submitted for culture at the MSU VDL in 2013 are now available. Equine and bovine pathogen AST profiles will become available in the future.

*Profiles are determined by following recommendations made by the Clinical and Laboratory Standards Institute (CLSI) Analysis and Presentation of Cumulative Antimicrobial Susceptibility Test Data; Approved Guideline – Third Edition (M39-A3, 2009), where possible. Percentages based on less than 30 isolates are noted and specimens submitted to the MSU VDL are not always collected at initial infection, nor can this status be determined from submittal records. The cumulative data may still provide valuable insight to our clients.

Routine MSU VDL Antimicrobial Panels

For Reference

Recently the American Veterinary Medical Association released a new resource for veterinarians: Antimicrobial-resistant pathogens affecting animal health. This includes a downloadable report as well as a poster, table, and species report cards for the following: dogs and cats, cattle, chickens and turkeys, fish and shrimp, horses, sheep and goats, and swine.