The primers were complemented positions 8–27 (primer 8F; 5′-AGAGTTTGATCCTGGCTCAG-3′), and 926–909 (primer 926R; 5′-CCGTCAATTCCTTTRAGTTT-3′) of the 16S rRNA of E. coli. Purified genomic DNA was isolated from each organism and used as template in a PCR reaction (1 ng of genomic DNA in total reaction volume of 20 μl, with a final magnesium concentration of 1.5 mM). The PCR conditions were as follows: one cycle at 94 °C for 5 min, followed by 35 cycles at 90 °C for 30 s, 57 °C for 30 s, 72 °C for 1 min, followed by a final 4 min incubation at 72 °C.