After 3 h, the cells were washed using fresh LB media, mixed with l-arabinose at the final concentration of 100 mM and incubated for another 2 h at 37 °C. Tenfold dilutions were made and plated on LB-Km and LB-Strep and incubated overnight at 37 °C. Colonies grown in LB-Km plates were considered to be unresolved and so were discarded, while those grown on LB-Strep plates were considered to be the required recombinants. The loss of the rpsL-neo

marker was confirmed by colony-PCR following the above-mentioned protocol. The ability of APEC1 click here wild type and its isogenic mutant APEC1LoxP to utilize ferric iron as the only source of iron was tested. Bacteria were cultured overnight at 37 °C in LB containing 200 μM of iron chelator 2, 2′-dipyridyl (DIP) (Sigma). The bacteria were then diluted 1 : 100 in LB containing 200 μM DIP and incubated for 3 h followed by washing in PBS. Approximately 1 × 105 CFU were mixed with 3 mL soft agar and plated onto LB plates supplemented with 375 μM DIP. Wells (5 mm diameter) were cut in the agar and filled with 100 μL of iron source (100 μM ferric chloride) or sterile double distilled water (negative control). Growth around wells was assessed

visually after an overnight incubation at 37 °C. For growth curves, strains were iron-limited overnight by culturing in LB containing 200 μM DIP. Prior to inoculation, strains were washed in PBS and approximately 105 CFU sdfd inoculated into liquid LB alone, LB containing 300 μM DIP, and 50 μM ferric chloride Y-27632 datasheet or no additional iron source and put into a 96-well plate. The general scheme of deletion is shown in Fig. 1a. PCR was performed buy Docetaxel using two primer sets HT51 and HT53, each containing 70 bp at the 5′ ends that are complimentary to regions upstream and downstream of the fiu gene and intergenic region 2051–52, followed by 34 bp for loxP site and 24 bp at the 3′ ends to amplify a cassette containing a rpsL-neo marker. The regions chosen for the deletion were designed based on the complete genome sequence of APEC O1 available

(Accession Number: NC_008563.1). The regions are the fiu gene, one of the 12 iron receptor genes in APEC (Ons et al., 2007) that encodes an iron-regulated outer membrane protein known as ferric iron uptake protein (Curtis et al., 1988; Newman & Shapiro, 1999) and an intergenic region 2051–52 between two divergently expressed genes APEC O1_2051 and APEC O1_2052 (Fig. 1b) (Johnson et al., 2007). The results from colony PCR demonstrated that the KmR recombinants analyzed contained the desired integration of LoxP cassette (Fig. 2) in respective regions and sequencing confirmed the integration and unidirectional orientation of loxP sites (data not shown). These results confirmed the generation of strains APEC1LoxP1 (Table 1) (Fig. 2a) and APEC1LoxP2 (Table 1) (Fig. 2b). The unidirectional orientation of the loxP sites is required for the deletion of the DNA segment (Nagy, 2000).