Background: Coexistence of bacteria and yeast in a myriad of microbial communities is indicative of their intimate relationship,
which could be the intracellular existence of bacteria inside yeast. In this study, the intracellular existence of bacteria inside yeast
and bacterial release from amphotericin B-treated yeasts was examined using polymerase chain reaction (PCR) and microscopy.
Methods: Released bacteria, B1 from Y1 (a gastric yeast) and B2 from Y2 (an oral yeast) were identified as Staphylococcus
hominis and Staphylococcus haemolyticus by biochemical tests as well as amplification of Staph-specific tuf and 16S rRNA
genes. PCR products were sequenced and matched with Staphylococcus published sequences in GenBank. PCR was also used
for amplification of Staph-tuf and Helicobacter pylori-16S rRNA genes from DNAs of 50 yeasts (20 oral, 20 gastric and 10 fecal).
Microscopy was used for observing bacterium-like bodies (BLBs) inside the yeasts vacuole.
Results: Thirty-two yeasts (64%) carried Staph-tuf gene, 20 yeasts (40%) carried H. pylori 16S rRNA gene, 14 yeasts (28%) carried
both genes, 12 yeasts (24%) carried neither, 6 yeasts (12%) carried only H. pylori 16S rRNA gene, and 18 yeasts (36%) carried only
tuf gene. Amplified products of tuf (370 bp) and 16S rRNA (756 bp) genes from B1 and Y1, and B2 and Y2 showed high similarity
to S. hominis and S. hemolyticus, respectively. Microscopic observations showed BLBs inside the yeasts vacuoles, which could be
related to the released bacteria. These BLBs were alive and could be observed in successive generations of yeasts.
Conclusion: Amplification of Staphylococcus- and H. pylori- specific genes from yeasts showed that the intracellular BLBs
could belong to Staphylococcus species and H. pylori. Release of culturable staphylococci from 2/50 (4%) yeasts showed that
not all yeasts release bacteria, and bacterial release takes place under unknown conditions. However, it could be triggered by
amphotericin B or hydrolytic enzymes. Coexistence of staphylococci and H. pylori genes could represent a mixed endosymbiotic
bacterial population in Fungi such as yeast. By selecting certain bacterial associates, the diversity of microbial communities could
be determined. These selected bacteria could have an intracellular origin, being released under certain conditions.