While tetraploidy is not uncommon in healthy subjects, it is usually not as high as the 20% observed. Furthermore, balanced translocations are not detected by array CGH. Hence, it is still plausible that the mucoepidermoid tumor did not include cross-contamination artifact from mesenchymal cells that migrated from the healthy tracheal tissue region surrounding the tumor location. We report that the LDK378 self-renewal and differentiation potential of MEi cells had overlapping properties to normal BM-MSC: obtaining a nearly homogenous immuno-phenotype displaying typical MSC characteristics, lacked in vivo tumor initiation capacity, demonstrated fibroblastoid colony forming ability and retained mesenchymal tri-lineage differentiation capacity i.e. osteoblasts, adipocytes and chondrocytes with and without growth factor induction. In contrast, there were distinct cellular differences noted between MEi cells and BM-MSCs. The cell proliferation rates of MEi cells between the early or late passages were exponentially increasing in cell numbers. The gene expression profiling showed however distinct differences between MEi cells and BM-MSCs with regard to genes relating to tube development, cell adhesion, angiogenesis, signal transduction, inflammatory response and regulation of programmed cell death. Unlike BM-MSCs, the MEi cells did not show expression of the Androgen receptor when tested by immunohistochemistry, but more sensitive microarrays found a 4-fold up-regulation of RNA when compared to BM-MSCs. The initial small size of the tumor biopsy did not easily allow for analysis of the frequency of MEi cells in the original sample. For this we instead developed a mathematical model from which we estimate a frequency of 17.5% MEi cells in the mucoepidermoid tumor cell mass. Intriguingly, we found the mucoepidermoid tumor cell mass may possibly contain niche cells. Immunocytochemistry staining of MEi cells revealed a small sub-population of MEI cells; 12.7% expressed b-III tubulin and 49.4% expressed GATA 6 were differentiating similarly like BM-MSCs. Assuming that the niche cells expressed both markers, the percentage of MEi cells that are niche cells is 6.3%. Given that 17.5% of the tumor cells are MEi cells, the percentage of tumor cells that are niche cells is therefore 1%. To our knowledge, the present study is the first report demonstrating a distinct population of benign human tracheal tumor cells with stem cell-like properties and warrants further studies on the role of these cells in initiation, development and/or progression of this type of tumor of the upper respiratory tract. Plasmids carrying antibiotic resistance genes are one of the primary sources of multidrug resistance in pathogens. Plasmids can be transferred to microorganisms through horizontal gene transfer, by methods such as conjugation and transformation, which can occur inside the hosts, as well as in the environment.