Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide:: a mechanism for virulence activation in the cystic fibrosis lung
Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide:: a mechanism for virulence activation in the cystic fibrosis lung
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DOI：
10.1099/13500872-145-6-1349
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发表时间：
1999-06-01
期刊：
影响因子：
2.8
通讯作者：
Kharazmi, A
中科院分区：
文献类型：
--
作者：
Mathee, K;Ciofu, O;Kharazmi, A
囊性纤维化（CF）患者死亡的主要原因是呼吸衰竭，这在很大程度上是由于铜绿假单胞菌菌株的慢性肺部感染，铜绿假单胞菌菌株经历粘液样转化，在体内显示生物膜生长模式并抵抗多形核白细胞（PMN）的浸润，其释放自由氧自由基如H2 O2感染CF患者的菌株中的粘液样表型表明称为藻酸盐的线性多糖的过量产生。为了模拟CF肺的炎症环境，铜绿假单胞菌PAO 1（一种典型的非粘液样菌株）在生物膜中生长。用低水平的H2 O2处理，好像是由PMN释放的，并观察到粘液变体的形成。这些类粘蛋白变体在编码抗α因子的mucA中具有突变;这导致表达藻酸盐生物合成操纵子所需的替代α因子（sigma（22）、AlgT或AlgU）的失调。所有测试的粘液变体均显示相同的突变，即mucA 22等位基因，这是CF分离株中常见的等位基因。当与光滑亲本菌株PAO 1相比时，粘液样mucA 22变体（i）产生2-6倍高水平的藻酸盐，（ii）在生长速率方面没有表现出可检测的差异，（iii）显示出未改变的LPS谱，（iv）诱导性β-内酰胺酶的量减少了72%，（v）分泌很少或临床部门没有LasA蛋白酶，仅显示44%。弹性蛋白酶活性通过N-末端序列分析，将与藻酸盐高产菌株相关的类似于54 kDa蛋白的特征鉴定为AlgE（Alg 76）。因此，包括基因工程改造的mucA 22突变体的类粘蛋白变体的共同表型表明，H2 O2处理导致的唯一突变是在mucA中。当铜绿假单胞菌生物膜在体外反复暴露于活化的PMN时，也观察到类粘蛋白变体，模拟体内观察。因此，PMN和它们的氧副产物可能导致铜绿假单胞菌经历对CF肺中的难治性mu-冷形式的典型适应。这些发现表明，细菌中的基因被有毒氧自由基激活，类似于在植物和哺乳动物细胞中发现的，可能是细菌的防御机制。这表明粘液转化是对氧自由基暴露的反应，并且该反应是细菌的防御机制。这是第一份报告表明，中性粒细胞和它们的氧自由基可以引起这种表型和基因型的变化，这是典型的难治性形式的铜绿假单胞菌在CF肺。这些发现可能为CF患者感染早期抗氧化和抗炎治疗的发展提供依据。
The leading cause of mortality in patients with cystic fibrosis (CF) is respiratory failure due in large part to chronic lung infection with Pseudomonas aeruginosa strains that undergo mucoid conversion, display a biofilm mode of growth in vivo and resist the infiltration of polymorphonuclear leukocytes (PMNs), which release free oxygen radicals such as H2O2 The mucoid phenotype among the strains infecting CF patients indicates overproduction of a linear polysaccharide called alginate. To mimic the inflammatory environment of the CF lung, P. aeruginosa PAO1, a typical non-mucoid strain, was grown in a biofilm. This was treated with low levels of H2O2, as if released by the PMNs, and the formation of mucoid variants was observed. These mucoid variants had mutations in mucA, which encodes an anti-a factor; this leads to the deregulation of an alternative a factor (sigma(22), AlgT or AlgU) required for expression of the alginate biosynthetic operon. All of the mucoid variants tested showed the same mutation, the mucA22 allele, a common allele seen in CF isolates. The mucoid mucA22 variants, when compared to the smooth parent strain PAO1, (i) produced 2-6-fold higher levels of alginate, (ii) exhibited no detectable differences in growth rate, (iii) showed an unaltered LPS profile, (iv) were similar to 72% reduced in the amount of inducible-beta-lactamase and (v) secreted little or Department of Clinical no LasA protease and only showed 44% elastase activity. A characteristic similar to 54 kDa protein associated with alginate overproducing strains was identified as AlgE (Alg76) by N-terminal sequence analysis. Thus, the common phenotype Of the mucoid variants, which included a genetically engineered mucA22 mutant, suggested that the only mutation incurred as a result of H2O2 treatment was in mucA. When a P. aeruginosa biofilm was repeatedly exposed to activated PMNs in vitro, mucoid variants were also observed, mimicking in vivo observations. Thus, PMNs and their oxygen by-products may cause P. aeruginosa to undergo the typical adaptation to the intractable mu- cold form in the CF lung. These findings indicate that gene activation in bacteria by toxic oxygen radicals, similar to that found in plants and mammalian cells, may serve as a defence mechanism for the bacteria. This suggests that mucoid conversion is a response to oxygen radical exposure and that this response is a mechanism of defence by the bacteria. This is the first report to show that PMNs and their oxygen radicals can cause this phenotypic and genotypic change which is so typical of the intractable form of P. aeruginosa in the CF lung. These findings may provide a basis for the development of anti-oxidant and anti-inflammatory therapy for the early stages of infection in CF patients.