Enumerating low densities of genetically engineered Erwinia carotovora in soil

An inexpensive, quantitative, and sensitive technique was developed for detection of genetically engineered Erwinia carotovora in soil samples. Enrichment media, antibiotic resistance, and most probable number (MPN) analysis were used to enumerate as few as 1 to 10 target cells/10 g soil. The MPN technique recovered significantly higher cell densities than plating; however, densities estimated by the two techniques were strongly correlated. After inoculation of soil microcosms with genetically engineered E. carotovora, a decline rate of 1.2 log units/g soil/10 days and then subsequent disappearance was observed using the MPN technique.