Porphyromonas gingivalis resistance to polymyxin B is determined by the lipid A 4'-phosphatase, PGN_0524 / 国际口腔科学杂志·英文版

<p><b>AIM</b>To elucidate the genetic basis for the pronounced resistance that the oral pathogen, Porphyromonas gingivalis (P. gingivalis), exhibits towards the cationic antimicrobial peptide, polymyxin B.</p><p><b>METHODOLOGY</b>A genetic screen of P. gingivalis clones generated by a Tn4400'-based random insertion mutagenesis strategy was performed to identify bacteria harboring novel genetic mutations that render P. gingivalis susceptible to killing by the cationic antimicrobial peptide, polymyxin B (PMB, 50 microg x mL(-1)).</p><p><b>RESULTS</b>P. gingivalis (ATCC 33277) is unusually resistant to the cationic antimicrobial peptide, PMB at relatively high concentrations (200 microg x mL(-1)). Approximately 2,700 independent Tn4400'-derived mutants of P. gingivalis were examined for increased sensitivity to PMB killing at a relatively low dose (50 microg x mL(-1)). A single PMB-sensitive mutant was obtained in this phenotypic screen. We determined that the Tn4400' transposon was integrated into the gene encoding the lipid A 4'-phosphatase, PGN_0524, demonstrating that this insertion event was responsible for its increased susceptibility of this clone to PMB-dependent killing. The resulting mutant strain, designated 0524-Tn4400', was highly sensitive to PMB killing relative to wild-type P. gingivalis, and exhibited the same sensitivity as the previously characterized strain, 0524KO, which bears a genetically engineered deletion in the PGN_0524 locus. Positive ion mass spectrometric structural (MALDI-TOF MS) analyses revealed that lipid A isolates from 0524-Tn4400' and 0524KO strains displayed strikingly similar MALDI-TOF MS spectra that were substantially different from the wildtype P. gingivalis lipid A spectrum. Finally, intact 0524-Tn4400' and 0524KO mutant bacteria, as well as their corresponding LPS isolates, were significantly more potent in stimulating Toll-like receptor 4 (TLR4)-dependent E-selectin expression in human endothelial cells relative to intact wild-type P. gingivalis or its corresponding LPS isolate.</p><p><b>CONCLUSION</b>The combined molecular evidence provided in this report suggests that PGN_0524, a lipid A 4'-phosphatase, is the sole genetic element conferring the ability of the periodontopathogen, P. gingivalis, to evade the killing activity of cationic antimicrobial peptides, such as PMB. These data strongly implicate PGN_0524 as a critical virulence factor for the ability of P. gingivalis to evade front-line host innate defenses that are dependent upon cationic antimicrobial peptide activity and TLR 4 sensing.</p>

[Chediak- Higashi Syndrome. report of one case]

Chediak - Higashi syndrome is a rare hereditary disease. Most patients develop an accelerated phase of the disease. Once accelerated phases occurred, the disease is invariably fatal before the use of etoposide. We report the case of a 5 year-old girl with consanguineous parents, presenting a partial oculocutaneaous hypopigmentation admitted because of protracted fever, lethargy, paler and hepatosplenomegaly. Laboratory results confirmed the diagnosis of hemophagocytic syndrome. The finding of a large cytoplasm granules in born marrow leucocytes confirmed the diagnosis of Chediak Higashi syndrome. Treatment with immunoglobulin, steroids and cyclosporine induced a transitory remission and a relapse occured after 3 weeks. The use of etoposide associated with precedent treatment leads to a prolonged remission and bone marrow transplantation was succefuly performed after 5 months. This case reports the severity of accelerated phase of Chediak- Higashi syndrome and the efficiency of the treatment with etoposide