Significant differences in the mean number of Spots per Cluster between Bp K96243 (wt) and Bp ∆hcp1 or Bp ∆bsaZ were observed (Figure  4C) and were probably due at least in part to an increase in the mean Cluster Area in Bp K96243 infected samples (see above). The inability to see an Tubastatin A increase in the total number of bacterial spots during the intracellular replication step (10 h post-infection) compared to early uptake or phagocytosis step (2 h post-infection) may partly be due to the killing of the internalized bacteria by the professional phagocytes. Although bacteria can be detected and quantitated by HCI, this technique it does not measure bacterial viability. Altogether,

these results show that the HCI MNGC assay can be implemented to quantitatively characterize mutant Bp strains phenotype based on cellular morphological changes induced in infected host cells. Furthermore, our HCI results regarding reduced MNGCs and bacterial spots following infection with

Bp ∆hcp1 or Bp ∆bsaZ mutants compared to wild CX-6258 in vitro type Bp at 10 h post-infection are consistent with previously published data [44, 58]. Figure 4 Validation of the MNGC assay (10 h post-infection). (A) Same as Figure  3A, except that macrophages were fixed at 10 h post-infection for different strains of Bp. Scale bar: 90 μm. (B) HCI quantification of learn more several cellular features of MNGC formation and (C) bacterial features from images acquired as described in Figure  3A. In B and C means +/- SD are shown of 6 replicates per plate, 3 plates run on independent days (n = 18). For each replicate

well >1000 nuclei were analyzed. **** p <0.0001; *** p < 0.001. Screening of a small molecule library in the MNGC assay To discover possible cellular pathways that are hijacked by Bp and that might regulate cell-to-cell fusion, we used the HCI MNGC assay to screen oxyclozanide a small, functionally focused collection of 43 compounds in duplicate. The compounds in this collection are annotated as targeting pathways involved in the epigenetic regulation of chromatin (See Experimental procedures for details). Bacterial infection induced epigenetic changes such as histone modifications, DNA methylation, chromatin remodeling, which in turn affect host cell signaling has been shown to either promote host defense or increase susceptibility to infection [71]. To investigate Bp induced epigenetic changes which in turn may modulate MNGC formation, RAW264.7 macrophages were first pre-treated with the compound library and then infected with Bp K96243. Cells treated with DMSO (Vehicle) and infected with Bp K96243 were considered as negative controls. At 8 h post-infection cells were fixed and processed in IF for the HCI MNGC assay as described above. Representative images of macrophages that were not infected (mock) or infected with Bp K96243 in presence of DMSO or identified hit compounds are shown in Figure  5A.