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. 2018 Jan;30(1):99-104.
doi: 10.1177/1040638717737589. Epub 2017 Oct 15.

Treatment history and antimicrobial susceptibility results for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni isolates from bovine respiratory disease cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015

Drew R Magstadt  1 , Adlai M Schuler  1 , Johann F Coetzee  1 , Adam C Krull  1 , Annette M O'Connor  1 , Vickie L Cooper  1 , Terry J Engelken  1
Affiliations

Treatment history and antimicrobial susceptibility results for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni isolates from bovine respiratory disease cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015

Drew R Magstadt et al. J Vet Diagn Invest. 2018 Jan.

Abstract

Bovine respiratory disease is the most costly disease facing the cattle industry. Increasing resistance to antimicrobial treatment has been presented as a significant contributing factor, often through summarized susceptibility testing data. We assessed the relationship between previous antimicrobial treatment and antimicrobial susceptibility results from isolates of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni cultured from bovine respiratory cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015. Antimicrobial susceptibility data from 1,251 bacterial isolates were included for analysis. More bacterial isolates from cattle that received antimicrobial treatment showed resistance compared to isolates from untreated cattle, and the percentage of resistant isolates increased as the number of antimicrobial treatments increased. Resistance to enrofloxacin, spectinomycin, tilmicosin, and tulathromycin was present in >75% of M. haemolytica isolates from cattle that had received 3 or more antimicrobial treatments; resistance to each of those 4 antimicrobials was present in ≤10% of M. haemolytica isolates from untreated cattle. Similar but less dramatic trends were apparent for isolates of P. multocida and H. somni. The percentage of multi-drug resistant bacterial isolates also increased with the number of treatments. Results of our study suggest that previous antimicrobial treatment may have a profound effect on antimicrobial susceptibility testing. Summarized susceptibility results from diagnostic laboratories should not be used to make generalized statements regarding trends in antimicrobial resistance without providing context regarding antimicrobial treatment history.

Keywords: Antimicrobial resistance; Histophilus; Mannheimia; Pasteurella; bovine respiratory disease; susceptibility testing.

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Conflict of interest statement

Declaration of conflicting interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Percentage of Mannheimia haemolytica isolates classified as resistant to selected antimicrobials determined by antimicrobial susceptibility testing, grouped by the number of antimicrobial treatments reported on the submission history.
Figure 2.
Figure 2.
Percentage of Pasteurella multocida isolates classified as resistant to selected antimicrobials determined by antimicrobial susceptibility testing, grouped by the number of antimicrobial treatments reported on the submission history.
Figure 3.
Figure 3.
Percentage of Histophilus somni isolates classified as resistant to selected antimicrobials determined by antimicrobial susceptibility testing, grouped by the number of antimicrobial treatments reported on the submission history.
Figure 4.
Figure 4.
Percentage of isolates of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni classified by the number of antimicrobial classes with resistant classifications, grouped by the number of antimicrobial treatments reported on the submission history (“Unknown” excluded).
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