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

Front Cell Infect Microbiol. 2018 Jun 8;8:192. doi: 10.3389/fcimb.2018.00192. eCollection 2018.


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 Coxiella burnetii 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 C. burnetii LpxC to LPC-011 in a surrogate E. coli model. In E. coli, the minimum inhibitory concentration (MIC) of LPC-011 against C. burnetii LpxC is < 0.05 μg/mL, a value lower than the inhibitor's MIC against E. coli LpxC. Considering the inhibitor's problematic pharmacokinetic properties in vivo and Coxiella'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 C. burnetii LpxC in cells. Under inhibitor treatment, Coxiella 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 C. burnetii by the inhibitor was shown in a phase II strain transformed with chlamydial kdtA. This exogenous KdtA enzyme modifies Coxiella lipid A with an α-Kdo-(2 → 8)-α-Kdo epitope that can be detected by anti-chlamydia genus antibodies. In inhibitor-treated THP-1 cells, Coxiella shows severe growth defects characterized by poor vacuole formation and low growth yields. Coxiella 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 Coxiella-containing vacuoles, and for robust multiplication of C. burnetii in macrophage-like THP-1 cells. Unlike many bacteria, C. burnetii replication in axenic media and non-phagocytic cells was less dependent on normal lipid A biosynthesis.

Keywords: Coxiella burnetii; LPC-011; LPS; LpxC inhibitor; Q fever; lipid A.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amidohydrolases / antagonists & inhibitors
  • Amidohydrolases / genetics
  • Animals
  • Axenic Culture / methods*
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / genetics
  • Chlorocebus aethiops
  • Coxiella burnetii / drug effects
  • Coxiella burnetii / growth & development*
  • Coxiella burnetii / pathogenicity*
  • Escherichia coli / drug effects
  • Escherichia coli / growth & development
  • Escherichia coli / pathogenicity
  • Humans
  • Hydroxamic Acids / pharmacology
  • Lipid A / antagonists & inhibitors*
  • Lipid A / genetics
  • Macrophages / drug effects
  • Macrophages / microbiology*
  • THP-1 Cells
  • Threonine / analogs & derivatives
  • Threonine / pharmacology
  • Vacuoles / drug effects
  • Vacuoles / microbiology
  • Vero Cells


  • Bacterial Proteins
  • Hydroxamic Acids
  • LPC-011
  • Lipid A
  • Threonine
  • Amidohydrolases
  • UDP-3-O-acyl-N-acetylglucosamine deacetylase