Cross contamination of Agrobacterium tumefaciens stocks with Escherichia coli are difficult to identify by microbiological techniques, leading to false negative results in transformation experiments. We have developed a genotyping assay for A. tumefaciens and E. coli lab strains based on amplification of 23S rDNA by PCR. Agrobacterium strains LBA 4404, C58 and EHA105 and E. coli DB3.1, DH5α and XL1-Blue can be identified separating the corresponding PCR amplicons in 2.5% agarose gels. However in crossed contaminations, interpretation of results is improved using melting point analysis on a quantitative PCR machine.This work was financed by the Fundación Séneca de la Región de Murcia and BIOCARM
