Objective    To evaluate the detection efficiency of 16S rRNA gene clone library in relative quantification of bacteria in the flora and its analyzing capacity to low-density bacteria.     Methods    In order to obtain definite background of experimental specimen

self-mixed bacterial suspensions including 9 kinds of bacteria in equal proportion or at gradient ratios were prepared to replace the conventional clinical bacterial samples. The suspensions were lyzed in presence or absence of mutanolysin

and then genomic DNA was extracted with common method. 16S rRNA gene clone library was established by amplifying targeted 16S rRNA gene conserved regions of the bacteria

purifying PCR products

inserting them to plasmid pGEM-T easy vector

transforming in DH5α

and cloning and sequencing the recombinants. Nucleotide sequences were blasted with GenBank database.     Results    For the bacterial suspension in equal proportion

all 9 bacteria were detectable when the genomic DNAs were extracted with or without mutanolysin. But for the bacterial suspension mixed at gradient ratios

all 9 bacteria were detectable when mutanolysin was used in lysis

and bifidobacterium at small amount was undetectable when DNA extraction was lyzed without mutanolysin. The bacterial ratios indicated by the library had certain correspondence to that in the mixed bacterial suspension

but not in a linear relationship.     Conclusion    The 16S rRNA gene sequences technology is a good method to analyze bacterial flora

capable of multiple bacterial dectection

and can relatively quantify the bacteria in the flora. It can indicate the abundance of the bacteria

but not their exact amounts.