The PCR mixture comprised 2 μl of DNA solution added to a final volume of 50 μl containing 0.2 μl of GoTaq Flexi DNA polymerase (5 U/μl Promega), 2 mM (each) dATP, dCTP, dGTP, and dTTP (Promega); 10 μl of 5x PCR buffer supplied by the manufacturer; 1 μM of each primers; 1 μL of dimethyl sulfoxide (Sigma) and 1.5 mM of MgCl2. The reactions
were carried out using a TC-512 thermal cycler (Techne). PCR conditions were as follows: 1 cycle of 5 min at 94°C; 30 cycles of 30 s at 94°C, 30 s at 55°C, and 30 s at 72°C; and 1 cycle of 7 min at 72°C. To detect presence or absence of each LSP, PCR products were analyzed by electrophoresis using 1.5% agarose gels. MIRU-VNTR analysis DNA in agarose plugs prepared for PFGE analysis was used for MIRU-VNTR analysis according to Stevenson et al. [23]. Small pieces of agarose plug, approximately 2 mm thick, were selleck chemical washed in TE buffer (pH 8) to remove residual EDTA in the storage buffer. One hundred
microlitres of TE buffer were added to the agarose and the sample boiled Cell Cycle inhibitor for 10 min to melt the agarose. Five microlitres were used for PCR and MIRU-VNTR analysis interrogating eight polymorphic loci was performed as described by Thibault et al.[11]. The allelic diversity (h) at a locus was calculated by using Nei’s index (see Additional file 3: Table S4) h = 1 − ∑ x i 2 n/(n − 1)], where x i is the frequency of the i th allele at the locus, and n the number of isolates [24]. Calculation of the discriminatory power The Simpson Discrimination Index (DI) described by Hunter and Gaston [25] was used as a numerical index for the discriminatory power of each typing method PFGE, IS900-RFLP and MIRU-VNTR and combinations of the typing methods (see Table 2 and Additional file 3: Table S4). The DI was calculated using next the following formula: Table 2 Discriminatory Index of IS 900 RFLP, MIRU-VNTR and SnaB1, Spe1 PFGE typing used alone and in combination Typing methods S type C type1 All types Subtypes I III I + III II IS900 RFLP No.2 10 14 24 35 59 DI 0.356 0.934 0.873 0.644 0.856 PFGE SnaB1 No. 5 10 15 24 39 DI 1.000 0.956 0.990 0.895 0.960 PFGE Spe1 No. 5 10 15 24 39 DI 1.000 0.978 0.990 0.801
0.924 PFGE (SnaB1-Spe1) No. 5 10 15 24 39 DI 1.000 1.000 1.000 1.000 1.000 MIRU-VNTR No. 10 14 24 35 59 DI 0.644 0.89 0.801 0.876 0.925 IS900 RFLP + MIRU-VNTR No. 10 14 24 35 59 DI 0.644 0.736 0.935 0.965 0.977 1: Panel of strains selected to represented the whole diversity of RFLP and MIRU-VNTR profiles of type C strains. 2: No. Number of strains analyzed. Where N is the total number of isolates in the typing scheme, s is the total number of distinct patterns discriminated by each typing method and strategy, and n j is the number of isolates belonging to the jth pattern.