Approximately 100,000 fungal species exist in the environment, but of these, only 300 species are known to cause animal or human infection34. Most of the fungal infections in humans are undiagnosed and under-reported35.
In this study, sixty fungal genera were discovered, and two opportunistic pathogenetic fungi genera, Phoma and Candida, were abundantly (45%) present in all 54 biopsy samples. Interestingly, Phoma only accounted for 2.8% of the fungi in oral rinse samples from healthy subjects21; however, this species was first observed as the predominant genus in intestinal biopsy samples of subjects with adenomas. As an opportunistic fungal pathogen, it has been reported that Phoma can cause lung mass36 and subcutaneous mycosis37, 38 and therefore may also be involved in the formation of adenomas.
In addition, Candida species, another opportunistic fungal pathogen22, 39 that rarely colonizes the gastrointestinal tracts of healthy subjects40, were also discovered in our study at a relatively high abundance (2.8%) in all biopsy samples. Candida spp. are able to form biofilms, which makes the genera a potential cause of nosocomial infections35, 41.
Moreover, Candida tropicalis, perhaps associated with fungal infection in severe ulcerative colitis22, was also found to be present in all 54 biopsy samples at relatively high abundance. Taken all together, these results further proved that the pathogenesis of the dominant fungus in intestinal mycobiota may be common among patients with adenomas and is also most likely involved in the development of adenomas.
Table 2 indicated that lower taxa were assigned fewer reads, indicating that the fungal database, especially the fungal database associated with humans, should be further expanded to provide more reference information for fungal mycobiota and to help identify potential fungi biomarkers in human gut illness.