DNA present in the aqueous phase was precipitated with 0.6 volumes of isopropanol and the DNA precipitate was washed with 70% (v/v) ethanol. The DNA pellet was dried using a lyophilizer and re-suspended in nucleasefree water. Universal bacterial primers corresponding to Escherichia coli positions 27F and 1492R were used for PCR amplification of 16S rRNA gene.