Isolation and identification of lactic acid bacteria from human tear.
Commensal bacterial variation, function, and the exact percentage of colonizedmicroflora on the human ocular surface remain unclear. In our prior research, the types and features of ocular surface disease and their relationship with microflora in atopic keratoconjunctivitis (AKC) have been evaluated using 16S rRNA gene clone library analysis. We found that a kind of lactic acid bacterial 16S rRNA gene was detected from all of the human tear samples. However, the DNA sequences provided by the 16S rRNA gene clone library method may not come from viable cells. To this end, we tried to culture ocular microflora of the human tear samples to prove the existence of viable lactic acid bacteria on the ocular surface. We firstly isolated 96 bacterial strains from culture samples of human tear, and screened them by 16S rRNA gene PCR method with lactic acid bacteria-specific primers. As a result, 5 positive strains were selected; however, further 16S rRNA gene full sequencing showed that most of the strains were annotated as non-lactic acid bacteria, Staphylococcus epidermidis, which is well known as a commensal microbe on the human skin. Therefore, we need more analysis to demonstrate the existence of lactic acid bacteria on human ocular surface.