Lipid A Has Significance for Optimal Growth of in Macrophage-Like THP-1 Cells and to a Lesser Extent in Axenic Media and Non-phagocytic Cells.

Lipid A is an essential basal component of lipopolysaccharide of most Gram-negative bacteria. Inhibitors targeting LpxC, a conserved enzyme in lipid A biosynthesis, are antibiotic candidates against Gram-negative pathogens. Here we report the characterization of the role of lipid A in growth in axenic media, monkey kidney cells (BGMK and Vero), and macrophage-like THP-1 cells by using a potent LpxC inhibitor -LPC-011. We first determined the susceptibility of LpxC to LPC-011 in a surrogate model. In , the minimum inhibitory concentration (MIC) of LPC-011 against LpxC is < 0.05 μg/mL, a value lower than the inhibitor's MIC against LpxC. Considering the inhibitor's problematic pharmacokinetic properties and 's culturing time up to 7 days, the stability of LPC-011 in cell cultures was assessed. We found that regularly changing inhibitor-containing media was required for sustained inhibition of LpxC in cells. Under inhibitor treatment, has reduced growth yields in axenic media and during replication in non-phagocytic cells, and has a reduced number of productive vacuoles in such cells. Inhibiting lipid A biosynthesis in by the inhibitor was shown in a phase II strain transformed with chlamydial . This exogenous KdtA enzyme modifies lipid A with an α-Kdo-(2 → 8)-α-Kdo epitope that can be detected by anti- genus antibodies. In inhibitor-treated THP-1 cells, shows severe growth defects characterized by poor vacuole formation and low growth yields. progenies prepared from inhibitor-treated cells retain the capability of normally infecting all tested cells in the absence of the inhibitor, which suggests a dispensable role of lipid A for infection and early vacuole development. In conclusion, our data suggest that lipid A has significance for optimal development of -containing vacuoles, and for robust multiplication of in macrophage-like THP-1 cells. Unlike many bacteria, replication in axenic media and non-phagocytic cells was less dependent on normal lipid A biosynthesis.