Freshly denatured driver DNA was added to further enrich the find more tester-specific sequences. The entire population of molecules was then subjected to PCR to amplify the desired tester-specific sequences using the primer corresponding to the T7 promoter sequence located in the adaptors. Only tester-specific sequences with two different adaptors are amplified exponentially. A second PCR amplification was performed using nested primers PF-02341066 in vivo to further reduce any background PCR products and enrich for tester-specific sequences. The resulting PCR products which were assumed to represent tester-specific DNA were cloned into plasmid pCR2.1 using the TOPO-TA cloning kit (Invitrogen, Germany) according to the
manufacturer’s recommendations. Southern blot Southern blot was performed using Roche® DIG DNA Labelling and Detection Kit (Roche, Shanghai, China) to prove whether the
DNA fragments cloned into plasmid pCR2.1 were present in the genome of CFT073 and MG1655 or not. First, the genomic DNA of the strains CFT073 and MG1655 was labelled by random primed labelling with digoxigenin according to the manufacturers manual. PCR products of the subtractive clones were transferred onto two identical positively charged nylon membranes. Hybridizations were performed using the labelled genomic DNA of the strains CX-4945 research buy CFT073 and MG1655, respectively. Chemiluminescent substrate reactions were carried out using the antidigoxigenin-AP Fab fragments and visualized with the CSPD ready to use (Roche, Shanghai, China). Cosmid library The cosmid library from APEC strain IMT5155 was created using the SuperCos 1 Cosmid Vector Kit (Stratagene, Amsterdam, Netherlands) following the vendor’s recommendations. DNA extraction Genomic DNA and Progesterone cosmid DNA was isolated using standard protocols . Plasmid DNA was isolated using the High Pure Plasmid Isolation Kit (Roche, Mannheim, Germany). PCR products were purified using the High Pure PCR Product Purification Kit, and DNA extraction from agarose gels was performed using the Agarose Gel DNA Extraction Kit (Roche, Mannheim, Germany) according to the manufacturer’s guidelines. PCR detection of aatA and flanking region variants
in E. coli The screening for aatA in a collection of 779 E. coli strains was performed by standard PCRs targeting three regions of the entire gene (amplicons A, B, and C). Oligonucleotide sequences (4031 to 4036) are listed in Additional file 1: Table S1, whereas their localization within the aatA ORF and respective amplicon sizes are given in Figure 1A. IMT5155 was used as a positive control, while CFT073 served as a negative control for all PCRs. To determine the genomic localization variants of aatA homologs in different strains, oligonucleotides aatA-FP and fecI-RP, eitD-RP and ykgN-RP were used in PCR experiments, respectively (Additional file 1: Table S1). Genomic DNA was used as template and 0.5 μl were added to a 25 μl reaction mixture containing the following: 0.