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In vitro trials of inhibitory drugs and investigation into oxygen susceptibility and culturing from feces of Macrorhabdus ornithogaster

Allison M. Bradley,1 Hanafusa Yasuko,2 and David N. Phalen1


Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, Texas1 and Department of Infectious Diseases, National Institute of Animal Health, Kannondai, Tsukuba, Ibaraki, Japan2

Objectives — The organism previously known as ‘megabacterium’ has recently been characterized as a novel yeast (Macrorhabdus ornithogaster) and successfully cultured.  This study attempted to identify treatment options, evaluate the toxicity of oxygen to the organism, and to culture the organism from feces.

Animals or sample population — Budgerigars (Melopsittacus undulatus) and cultures of M. ornithogaster obtained from them.

Procedures — Various concentrations of ten antifungal agents were inoculated with a known concentration of cells in custom growth medium and incubated.  Feces from budgerigars shedding low concentrations of the organism were placed into culture medium and incubated.  M. ornithogaster’s susceptibility to oxygen was evaluated by comparing growth following exposure to room air for zero and eight hours.  Growth was evaluated via optical density and/or cell counts.

Results — Gentian violet, potassium sorbate, sodium benzoate, and potassium benzoate inhibited growth at all concentrations tested.  Nystatin, fluconazole, and amphotericin B inhibited growth at high concentrations.  Sodium acetate inhibited growth at high concentrations and enhanced growth at low concentrations.  Effectiveness of fumagillin and ammonium molybdate was less conclusive.  Oxygen exposure had limited impact on growth.  M. ornithogaster was not cultured from feces.

Conclusions and clinical relevance — In vitro antifungal susceptibility testing of M. ornithogaster is practical, and several promising drugs have been identified.  Changes in growth are minimal following short-term oxygen exposure.  Longer exposure periods are being tested. Cells shed in feces may not be viable.  However, greater success may be achieved by using birds shedding higher numbers of organisms.