Cationic Antimicrobial Peptide Resistance in Neisseria meningitidis

Abstract

Cationic antimicrobial peptides (CAMPs) are important components of the innate host defense system against microbial infections and microbial products. However, the human pathogen Neisseria meningitidis is intrinsically highly resistant to CAMPs, such as polymyxin B (PxB) (MIC > 512 g/ml). To ascertain the mechanisms by which meningococci resist PxB, mutants that displayed increased sensitivity (>4-fold) to PxB were identified from a library of mariner transposon mutants generated in a meningococcal strain, NMB. Surprisingly, more than half of the initial PxB-sensitive mutants had insertions within the mtrCDE operon, which encodes proteins forming a multidrug efflux pump. Additional PxB-sensitive mariner mutants were identified from a second round of transposon mutagenesis performed in an mtr efflux pump-deficient background. Further, a mutation in lptA, the phosphoethanolamine (PEA) transferase responsible for modification of the lipid A head groups, was identified to cause the highest sensitivity to PxB. Mutations within the mtrD or lptA genes also increased meningococcal susceptibility to two structurally unrelated CAMPs, human LL-37 and protegrin-1. Consistently, PxB neutralized inflammatory responses elicited by the lptA mutant lipooligosaccharide more efficiently than those induced by wild-type lipooligosaccharide. mariner mutants with increased resistance to PxB were also identified in NMB background and found to contain insertions within the pilMNOPQ operon involved in pilin biogenesis. Taken together, these data indicated that meningococci utilize multiple mechanisms including the action of the MtrC-MtrD-MtrE efflux pump and lipid A modification as well as the type IV pilin secretion system to modulate levels of CAMP resistance. The modification of meningococcal lipid A head groups with PEA also prevents neutralization of the biological effects of endotoxin by CAMP.

Phosphoethanolamine Decoration of Neisseria gonorrhoeae Lipid A Plays a Dual Immunostimulatory and Protective Role during Experimental Genital Tract Infection

“…8A). A similar observation was reported by Tzeng et al (16) in studies with an lptA mutant of N. meningitidis, and based on the capacity of PMB to differentially neutralize modified and unmodified lipid A, we hypothesized that host-derived CAMPs may contribute to the differences in the inflammatory potentials of wild-type and lptA mutant gonococci observed in (open bars) gonococci was incubated with PMB (10 g/ml) or 10 g of CRAMP-38, human LL-37, or lysozyme and then tested for its capacity to induce NF-B expression in MEFs or bind to the LAL reagent. (A) SEAP activity produced by MEFs; (B) LAL activity.…”

“…PEA decoration of heptose II of the oligosac-charide core of the lipooligosaccharide (LOS) ␤-chain, in contrast, reduces resistance to PMB in Neisseria meningitidis but has no effect in N. gonorrhoeae. The presence of a lipid A PEA moiety also increases N. gonorrhoeae resistance to complement-mediated killing (15,16) but does not affect the serum resistance of N. meningitidis. We recently demonstrated that an lptA mutant of N. gonorrhoeae strain FA1090 was attenuated during experimental urethral infection of male subjects and cervicovaginal infection of female mice (17), which strongly supports the protective role of this lipid A modification during infection.…”

Structure of a lipid A phosphoethanolamine transferase suggests how conformational changes govern substrate binding

“…An update of the nomenclature for all Neisserial lipid A PEA transferase enzymes will be announced on PubMLST (pubmlst.org/)]. Mutants of NmEptA increase bacterial sensitivity to CAMPs (12), resulting in attenuation in mice and human models of infection (13). EptA catalyzes the transfer of PEA from phosphatidylethanolamine (PE), via a PEA-enzyme intermediate, to the 1 and 4′ headgroups of the lipid A of lipooligosaccharide (SI Appendix, Scheme S1).…”

Antimicrobial Proteins and Their Importance in Immunity

“…Katyonik antimikrobiyel proteinler 3 temel kategoride sınıflandırılırlar. Bunlar prolin bakımından zengin lineer proteinler, α-heliks formundaki lineer proteinler ile sistein içeren  tabaka proteinlerdir 3,4 .…”