Abstract:

The number of bacteria in milk has gained growing attention as the new national dairy standard is
implemented. However, few people are concerned about its bacterial species and flora. Bacterial communities in
milk samples from 4 manufactures were analyzed. Bacterial genome DNA was extracted from milk and molecular
segments of the V3 region of the 16S rRNA gene was obtained by PCR, cloning and sequencing. Bacterial species,
diversity and flora were analyzed by bioinformatics. Bacterial counts of samples were measured by florescent
real-time quantitative PCR. The results showed that molecular segments of the V3 region in the 16S rRNA
existed in large quantities in milk. Among 472 clones of the V3 region in the 16S rRNA obtained from sequencing,
452 could be clearly classified to genera, including 3 Gram-positive (G+) and 14 Gram-negative (G-) species,
and 20 others could be classified to the class level. These results indicated that the bacterial counts were all at a
high level in different milk. Samples from 4 manufactures differed in their bacterial communities, and the diversity
of bacterial flora was obviously different.

Key words: commercial milk, 16S rRNA, bacterial flora, bacterial count