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In vitro antimicrobial activity against reference strains and field isolates of Treponema hyodysenteriae
K Kitai1, M Kashiwazaki, Y Adachi
1Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan.
Abstract:
The in vitro susceptibilities of eight isolates of Treponema hyodysenteriae from pigs naturally infected with swine dysentery between 1976 and 1983 were determined by an agar dilution technique. Carbadox, olaquindox, tiamulin, metronidazole, furazolidone, and monensin were the most active against these field isolates regardless of the year of recovery. The influence of inoculum size on the MICs against four reference strains of T. hyodysenteriae was studied. Various degrees of activities of ampicillin and lincomycin were found, depending on the inoculum size. The effect of successive in vitro subcultures on the susceptibility of a reference strain of T. hyodysenteriae was examined. The strain resistant to tylosin became susceptible to the drug.
Insights
Eight Treponema hyodysenteriae isolates showed consistent susceptibility to several key antimicrobials between 1976-1983. In vitro studies also revealed inoculum size impacts antibiotic activity and tylosin resistance can be reversed with subculturing.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Swine Health
Background:
- Swine dysentery, caused by Treponema hyodysenteriae, is a significant enteric disease in pigs.
- Understanding antimicrobial susceptibility is crucial for managing swine dysentery outbreaks.
- Historical data on antimicrobial resistance patterns can inform current treatment strategies.
Purpose of the Study:
- To determine the in vitro antimicrobial susceptibility of Treponema hyodysenteriae field isolates.
- To investigate the impact of inoculum size on minimum inhibitory concentrations (MICs).
- To examine the effect of in vitro subculturing on antimicrobial susceptibility, particularly for tylosin.
Main Methods:
- Agar dilution technique used to test susceptibility of eight T. hyodysenteriae field isolates.
- MICs determined for various antimicrobials including carbadox, olaquindox, tiamulin, metronidazole, furazolidone, and monensin.
- Inoculum size effects studied using four T. hyodysenteriae reference strains.
- In vitro subculturing performed to assess changes in susceptibility of a reference strain.
Main Results:
- Carbadox, olaquindox, tiamulin, metronidazole, furazolidone, and monensin demonstrated consistent activity against field isolates from 1976-1983.
- Ampicillin and lincomycin activity varied depending on inoculum size.
- A tylosin-resistant strain regained susceptibility after successive in vitro subcultures.
Conclusions:
- Several key antimicrobials remain effective against Treponema hyodysenteriae field isolates over time.
- Inoculum size is an important factor influencing the interpretation of in vitro antimicrobial susceptibility data.
- Reversal of acquired antimicrobial resistance is possible through specific in vitro conditions, suggesting potential therapeutic implications.