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Relationship between antimicrobial susceptibility of clinical mastitis pathogens and treatment outcome in cows

Fernanda G H Hoe1, Pamela L Ruegg

  • 1Department of Dairy Science, University of Wisconsin, Madison, WI 53706, USA.

Journal of the American Veterinary Medical Association
|November 11, 2005
PubMed
Abstract

Insights

In vitro antimicrobial susceptibility testing did not predict treatment outcomes for cows with mild to moderate mastitis. This study suggests susceptibility testing may not be reliable for guiding intramammary mastitis therapy.

Area of Science:

  • Veterinary Medicine
  • Bacteriology
  • Animal Health

Background:

  • Clinical mastitis is a significant concern in dairy cattle, impacting animal welfare and economic productivity.
  • Antimicrobial susceptibility testing (AST) is often used to guide treatment decisions for bacterial infections.
  • The efficacy of AST in predicting treatment outcomes for bovine mastitis, particularly with intramammary therapies, requires further investigation.

Purpose of the Study:

  • To investigate the association between in vitro antimicrobial susceptibility testing results of mastitis pathogens and the clinical outcome of treatment in cows.
  • To evaluate whether pathogen susceptibility or resistance to pirlimycin influences treatment duration and cure rates in clinical mastitis cases.

Main Methods:

  • An observational study was conducted involving 133 cows diagnosed with mild or moderate clinical mastitis in a single quarter.
  • Cows received intramammary infusions of pirlimycin, with treatment duration and clinical cure noted.
  • Bacterial isolates were subjected to antimicrobial susceptibility testing using a broth micro-dilution technique.

Main Results:

  • Environmental streptococci, coliforms, and coagulase-negative Staphylococcus spp. were the most frequently isolated pathogens.
  • No significant differences in treatment duration or days to clinical cure were observed between cows with susceptible or resistant isolates.
  • Bacteriologic cure rates at 14 and 21 days post-treatment did not differ significantly based on isolate susceptibility.

Conclusions:

  • The study did not identify a correlation between in vitro antimicrobial susceptibility testing results and clinical outcomes in cows with mild or moderate mastitis.
  • Current evidence does not support the use of in vitro susceptibility testing to guide intramammary mastitis treatment decisions.
  • Further research may be needed to explore alternative or complementary diagnostic approaches for optimizing mastitis therapy.

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