Phosphoethanolamine Transferase LptA in Haemophilus ducreyi Modifies Lipid A and Contributes to Human Defensin...

Area of Science:

• Microbiology
• Immunology
• Bacterial Pathogenesis

Background:

• Haemophilus ducreyi evades human antimicrobial peptides (APs), including defensins and LL-37.
• AP resistance is vital for H. ducreyi virulence, with LL-37 resistance mediated by the Sap transporter.
• Cationic APs target negatively charged bacterial surfaces; positive modifications on lipooligosaccharide (LOS) confer resistance via electrostatic repulsion.

Purpose of the Study:

• To investigate the role of phosphoethanolamine (PEA) transferases in H. ducreyi antimicrobial peptide resistance.
• To identify genes responsible for PEA modification of LOS in H. ducreyi.
• To determine the contribution of PEA modifications to H. ducreyi virulence in vivo.

Main Methods:

• Generated non-polar, unmarked mutants of H. ducreyi lacking one, two, or all three putative PEA transferase genes (lptA, ptdA, ptdB).
• Assessed mutant susceptibility to α-defensins, β-defensins, and LL-37.
• Analyzed cell surface charge and LOS PEA modification using mass spectrometry.
• Evaluated virulence of the triple mutant in human inoculation experiments.

Main Results:

• The triple PEA transferase mutant showed significantly increased susceptibility to α- and β-defensins.
• Deletion of all three genes increased bacterial cell surface negativity.
• LptA was identified as the primary PEA transferase for lipid A modification; PtdA and PtdB had no significant effect on LOS PEA modification.
• The triple mutant exhibited virulence comparable to the parent strain in human infections.

Conclusions:

• This study identifies PEA modification of lipid A by LptA as a novel mechanism for α-defensin resistance in H. ducreyi.
• Despite increased defensin susceptibility, the triple mutant's virulence was unaffected, suggesting LL-37 resistance is more critical for pathogenesis.
• Findings highlight distinct resistance mechanisms against different classes of antimicrobial peptides in H. ducreyi.