FIG. 4.

Amplification of E. coli 16S rRNA from nonsterile soil inoculated with various densities of E. coli. (A) Ethidium bromide-stained agarose gel; (B) Southern hybridization of gel from panel A to EUB338. Lanes: 1, 100-bp DNA ladder; 2, no template; 3, 10 ng of DNA extract template from nonsterile, nonseeded soil sample; 4 to 18, 10 ng of DNA extract template from nonsterile soil samples seeded with stationary-phase E. coli at 7 × 10⁴, 7 × 10⁵, 2 × 10⁶, 7 × 10⁶, and 7 × 10⁷ CFU g⁻¹, respectively.