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Published on: June 11, 2020
Growth and metabolic characterization of Macrorhabdus ornithogaster
Yasuko Hannafusa1, Allison Bradley, Elizabeth E Tomaszewski
1Department of Infectious Diseases, National Institute of Animal Health, Kannondai, Tsukuba, Ibaraki, Japan.
Abstract:
Macrorhabdus ornithogaster (M. ornithogaster) is an anamorphic ascomycetous yeast found only in the stomach of birds. Infection is often benign but has also been associated with disease in some species of birds under some circumstances. In vitro efforts to grow M. ornithogaster have been largely unsuccessful. In this report, multiple liquid and solid media of varying pH, sugar concentration, and fetal bovine serum (FBS) concentrations, incubated at various temperatures in room air or microaerophilic conditions, were examined for their ability to support the growth of M. ornithogaster, obtained from a budgerigar (Melopsittacus undulatus). Optimum growth conditions were found to be Basal Medium Eagle's, pH 3 to 4, containing 20% FBS, and 5% glucose or sucrose under microaerophilic conditions at 42 degrees C. Using these conditions, M. ornithogaster was repeatedly passaged without loss of viability. Polyclonal isolates of M. ornithogaster consistently assimilated glucose, sucrose, and trehalose. M. ornithogaster did not grow with prolonged exposure to atmospheric oxygen, but growth in microaerophilic conditions was moderately enhanced by preincubation with atmospheric oxygen for 24 hours. An isolate of M. ornithogaster was found to be infective to day-old chickens, reduce their rate of weight gain, and induce a mild to moderate heterophilic inflammation of the isthmus. M. ornithogaster was reisolated from the chicks 7 days after infection, fulfilling Koch's postulates. A 761-bp sequence of 18S rDNA from this isolate was compared to the originally reported M. ornithogaster sequence and was found to be 97% identical.
Insights
Researchers successfully cultured Macrorhabdus ornithogaster (M. ornithogaster), a yeast affecting birds, under specific microaerophilic conditions. This breakthrough in avian microbiology enables further study of M. ornithogaster infections.
Area of Science:
- Avian microbiology
- Yeast cultivation
- Infectious disease
Background:
- Macrorhabdus ornithogaster (M. ornithogaster) is an anamorphic yeast found in bird stomachs.
- While often benign, M. ornithogaster can cause disease in certain bird species.
- Previous in vitro cultivation attempts have largely failed.
Purpose of the Study:
- To determine optimal in vitro growth conditions for Macrorhabdus ornithogaster.
- To establish a reproducible method for culturing M. ornithogaster.
- To assess the pathogenicity of M. ornithogaster in a host model.
Main Methods:
- Tested various liquid and solid media with differing pH, sugar, and fetal bovine serum (FBS) concentrations.
- Incubated cultures at various temperatures under room air and microaerophilic conditions.
- Inoculated day-old chickens to assess infectivity and pathogenicity, reisolating the yeast to fulfill Koch's postulates.
Main Results:
- Optimized growth achieved in Basal Medium Eagle's at pH 3-4 with 20% FBS and 5% glucose/sucrose, microaerophilically at 42°C.
- M. ornithogaster assimilated glucose, sucrose, and trehalose.
- Infection in chickens reduced weight gain and caused inflammation; M. ornithogaster was reisolated, confirming infectivity.
Conclusions:
- Established optimal conditions for M. ornithogaster in vitro culture.
- Demonstrated the infectivity and pathogenicity of M. ornithogaster in chickens.
- Provided a foundation for further research into M. ornithogaster pathogenesis and treatment.
