001) difference in growth as compared to WT, which had survived better during this time period. The mutant MAV_5106

largely differed from other mutants and during four days of infection had shown constant survival (Figure  6 B). The capacity of mutant MAV_5106 to survive better in macrophages suggests that it may be characterised by a higher virulence as compared to the other mutants. Tateish et al.[70] compared the virulence of different M. avium isolates in humans, immuno-competent mice and THP-1 cells. They found that the strain causing the most serious disease in humans and the highest bacterial load in mouse lungs also grew better in THP-1 cells than the other strains tested. According to this, the mutants MAV_4334, MAV_1778 and MAV_3128 may display reduced virulence and the corresponding genes may represent virulence-associated genes. Figure 6 Intracellular https://www.selleckchem.com/products/cb-839.html survival of mutants compared to WT in human monocytes. Human blood monocytes (1.0×106) from healthy volunteers were infected (MOI 10) with mutants and WT. BVD-523 nmr Intracellular bacteria were quantified after 4 hour of infection, and after 1, 2, & 4 days. The monocytes were lysed in 1 ml of sterile water and 100 μl of 1:500 dilution in sterile water of sample were plated on Middlebrook agar plates supplemented with ADC for CFU counting. A: WT and mutant MAV_4334; B: WT and mutant MAV_5106; C: WT and mutant MAV_1778; D: WT and mutant MAV_3128. Statistical

analysis was done using a two tailed, paired Student’s t test. When compared to wild-type a P < 0.05 was considered significant (*) and a P < 0.01 very significant (**). Evaluation of the screening procedure We have employed five screening methods (colony morphology, pH stress resistance, amoeba resistance, cytokine induction, intracellular survival) to select mutants affected in virulence-related traits. Two mutants (MAV_4334 and MAV_3128) responded differently from the WT in four of these five screening tests and two mutants (MAV_5106 and MAV_1778) reacted differently in three screening tests. The most prominent differences

were exhibited by mutant MAV_3128. The other mutants either did not show any differences compared to the WT or reacted differently in only one or two tests. The insertions HSP90 in mutants MAV_4334, MAV_5106, MAV_1778 and MAV_3128 have been mapped and the structure of the mutated regions has been analyzed on nucleotide level. In all cases only one gene has been Z-VAD-FMK mw mutagenised. The insertions are located in the genes MAV_4334 (nitrogenase reductase family), MAV_5106 (phosphoenolpyruvate carboxykinase), MAV_1778 (GTP-binding protein LepA) and MAV_3128 (lysyl-tRNA synthestase LysS). Phosphoenolpyruvate carboxykinases (PEPCK) catalyse the reversible decarboxylation and phosphorylation of oxaloacetate to form phosphoenolpyruvate. Mutations of the PEPCK gene from M. bovis BCG are characterised by attenuated virulence and reduced survival in macrophages [72]. The PEPCK gene from M.