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Use of a proposed antimicrobial susceptibility testing method for Haemophilus parasuis
Denise Ann E Dayao1, Marco Kienzle2, Justine S Gibson1
1The University of Queensland, School of Veterinary Science, Gatton, Qld, 4343, Australia.
Abstract:
The aim of this study was to examine the antimicrobial susceptibility of 97 Haemophilus parasuis cultured from Australian pigs. As there is no existing standard antimicrobial susceptibility technique available for H. parasuis, methods utilising the supplemented media, BA/SN for disc diffusion and test medium broth (TMB) for a microdilution technique, were initially evaluated with the reference strains recommended by the Clinical and Laboratory Standards Institute. The results of the media evaluation suggested that BA/SN and TMB can be used as suitable media for susceptibility testing of H. parasuis. The proposed microdilution technique was then used with 97 H. parasuis isolates and nine antimicrobial agents. The study found that Australian isolates showed elevated minimum inhibitory concentrations (MICs) for ampicillin (1%), penicillin (2%), erythromycin (7%), tulathromycin (9%), tilmicosin (22%), tetracycline (31%) and trimethoprim-sulfamethoxazole (40%). This study has described potential antimicrobial susceptibility methods for H. parasuis and has detected a low percentage of Australian H. parasuis isolates with elevated antimicrobial MICs.
Insights
This study evaluated antimicrobial susceptibility methods for Haemophilus parasuis in Australian pigs. Elevated minimum inhibitory concentrations (MICs) were found for several antimicrobials, including tetracycline and trimethoprim-sulfamethoxazole.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Swine Health
Background:
- Haemophilus parasuis is a significant swine pathogen.
- Standardized antimicrobial susceptibility testing (AST) methods for H. parasuis are lacking.
- Monitoring antimicrobial resistance in H. parasuis is crucial for effective treatment strategies.
Purpose of the Study:
- To evaluate suitable methods for antimicrobial susceptibility testing of H. parasuis.
- To determine the antimicrobial susceptibility profile of Australian H. parasuis isolates.
- To identify potential emerging resistance trends in H. parasuis.
Main Methods:
- Evaluation of supplemented media (BA/SN for disc diffusion, TMB for microdilution) using reference strains.
- Application of a validated microdilution technique for AST.
- Testing of 97 H. parasuis isolates against nine antimicrobial agents.
Main Results:
- BA/SN and TMB were confirmed as suitable media for H. parasuis AST.
- Elevated minimum inhibitory concentrations (MICs) were observed in Australian isolates.
- Specific elevated MICs were noted for ampicillin (1%), penicillin (2%), erythromycin (7%), tulathromycin (9%), tilmicosin (22%), tetracycline (31%), and trimethoprim-sulfamethoxazole (40%).
Conclusions:
- Established and validated potential AST methods for H. parasuis.
- Detected a low prevalence of Australian H. parasuis isolates with elevated antimicrobial MICs.
- Highlights the need for ongoing surveillance of antimicrobial resistance in swine pathogens.
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