Diversity of lactic acid bacteria in Thai fermented pork (nham) during fermentation assessed by denaturing gradient gel electrophoresis

摘要

This work presents the study of lactic acid bacteria (LAB) diversity in Thai fermented pork (nham) at different time points of the fermentation by denaturing gradient gel electrophoresis (DGGE) technique. Total DNA extracted from two nham samples, fermented with and without Lactobacillus plantarum starter culture, were amplified using primers targeted at V3 region of the 16S rRNA gene of bacteria. DNA bands appeared on DGGE gels were cloned and sequenced for species identification. The results showed that the LAB species in both nham samples at the beginning of fermentation was diverse and at least 15 species were detected. The number of species was then reduced dramatically during the first 2 days of fermentation. Two main species, i.e. Lactococcus garvieae and Lactococcus lactis were found from day 2 to day 15. In nham fermented with starter culture, the DGGE band corresponding to the Lb. plantarum was evident from the beginning to the end of the test period. However, in nham without starter culture, although no Lb. plantarum was added and no corresponding band appeared at the beginning of fermentation, the band gradually appeared as faint band on day 3 and increased in intensity as fermentation progressed. Similar pattern was also observed on the band corresponding to Pediococcus pentosaceus. This phenomenon suggested that Lb. plantarum and P. pentosaceus can be established successfully and may play an important role in nham fermentation system. This study also reported co-migration of different DNA species to the same DGGE-band position as well as fragments with the same DNA sequence may also migrated to different position on the DGGE gel. Therefore, the number of DGGE bands could not be used to identify the number of bacterial species in the sample accurately.