[42]. One million macrophages were seeded per well in 24-well cell culture plates, with three to five wells per sample per sampling point. Infection with mutants, complemented BLZ945 clinical trial strain and WT, Amikacin treatment and sampling were done as described above for THP-1 cells infection, except that human monocytes were pre-activated with 100 U ml-1 of human IFN-γ (Invitrogen, Darmstadt, Germany) and 10 ng ml-1 of LPS

(Sigma), IMDM was used for washing, the MOI for infection was 10 and the dilution of the samples for plating and counting of CFU was 1:500. Results and discussion Generation and genetic characterisation of M. avium mutants Our aims were the establishment of a new method to mutagenise MAH and the identification of mutants potentially affected in virulence. The mutagenesis

approach involved transformation of a recombination substrate by electroporation into MAH, and we therefore first identified clinical and environmental MAH strains applicable to electroporation. We considered a prior investigation Selleck PARP inhibitor of transformability to be necessary, because other authors had reported some clinical M. avium strains to be inaccessible to electroporation [43]. As proposed by Lee et al.[43], we chose a gfp-containing plasmid (pGFP: gfp this website cloned in vector pMV261 [38]) for transformation assays. We tested 14 clinical isolates and two soil isolates. Strain M. avium 104 was originally isolated from an HIV patient [44] and strains 2721/04, 10091/06, 10203/06, 4557/08,

4023/08, 3646/08, 3449/08, 3269/08, 2630/08, 2014/08, 772/08, 709/08, 528/08 were isolated from children with lymphadenitis. Strains 128 and 129 are soil isolates. Out of these 16 M. avium strains, five (104, 2721/04, 2014/08, 4023/08 and 528/08) could be transformed with pGFP. As the genome sequence from M. avium strain 104 is available in the genome data bases, simplifying a precise mutant description, we decided to concentrate on this strain for further analysis. Our mutagenesis approach took advantage of the high rate of illegitimate recombination in slow growing mycobacteria [28, 45] and their ability to take up linear DNA [29]. For selection purposes we chose the Hygr gene instead of also often click here used Kanamycin resistance gene (Kmr), because the Hygr gene had been shown before to be superior to the Kmr gene especially for the transformation of other than laboratory strains [46]. The Hygr gene used for electroporation was flanked by plasmid DNA of 793 bp on one side and 238 bp on the other side. These flanking regions served as substrates for the illegitimate recombination. After electroporation of 3–6 μg of restriction fragment and selection on plates containing Hygromycin, about 1000 colonies could be obtained.