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Abstract：
The Burkholderia cepacia complex (Bcc) is a group of Gram-negative opportunistic bacteria often associated with fatal pulmonary infections in patients with impaired immunity, particularly those with cystic fibrosis (CF) and chronic granulomatous disease (CGD). Some Bcc strains are known to naturally produce pyomelanin, a brown melanin-like pigment known for scavenging free radicals; pigment production has been reported to enable Bcc strains to overcome the host cell oxidative burst. In this work, we investigated the role of pyomelanin in resistance to oxidative stress and virulence in strains J2315 and K56-2, two epidemic CF isolates belonging to the Burkholderia cenocepacia ET-12 lineage. We previously reported that a single amino acid change from glycine to arginine at residue 378 in homogentisate 1,2-dioxygenase (HmgA) affects the pigment production phenotype: pigmented J2315 has an arginine at position 378, while non-pigmented K56-2 has a glycine at this position. Herein, we performed allelic exchange to generate isogenic non-pigmented and pigmented strains of J2315 and K56-2, respectively, and tested these to determine whether pyomelanin contributes to the protection against oxidative stress in vitro as well as in a respiratory infection in CGD mice in vivo. Our results indicate that the altered pigment phenotype does not significantly impact these strains\' ability to resist oxidative stress with H2O2 and NO in vitro and did not change the virulence and infection outcome in CGD mice in vivo suggesting that other factors besides pyomelanin are contributing to the pathophysiology of these strains.IMPORTANCEThe Burkholderia cepacia complex (Bcc) is a group of Gram-negative opportunistic bacteria that are often associated with fatal pulmonary infections in patients with impaired immunity, particularly those with cystic fibrosis and chronic granulomatous disease (CGD). Some Bcc strains are known to naturally produce pyomelanin, a brown melanin-like pigment known for scavenging free radicals and overcoming the host cell oxidative burst. We investigated the role of pyomelanin in Burkholderia cenocepacia strains J2315 (pigmented) and K56-2 (non-pigmented) and performed allelic exchange to generate isogenic non-pigmented and pigmented strains, respectively. Our results indicate that the altered pigment phenotype does not significantly impact these strains\' ability to resist H2O2 or NO in vitro and did not alter the outcome of a respiratory infection in CGD mice in vivo. These results suggest that pyomelanin may not always constitute a virulence factor and suggest that other features are contributing to the pathophysiology of these strains.
摘要：
洋葱伯克霍尔德氏菌（Bcc）是一组革兰氏阴性机会性细菌，通常与免疫力受损患者的致命肺部感染有关，特别是那些囊性纤维化（CF）和慢性肉芽肿病（CGD）。已知一些Bcc菌株天然产生pyomelanin，一种棕色黑色素样色素，以清除自由基而闻名；据报道，色素的产生使Bcc菌株能够克服宿主细胞的氧化爆发。在这项工作中,我们研究了pyomelanin在J2315和K56-2菌株中对氧化应激和毒力的抗性中的作用，J2315和K56-2是两种流行的CF分离株，属于伯克霍尔德氏菌ET-12谱系。我们先前报道过，匀浆1,2-双加氧酶（HmgA）中残基378处的单个氨基酸从甘氨酸变为精氨酸会影响色素的产生表型：色素J2315在378位具有精氨酸，而非色素K56-2在该位置具有甘氨酸。在这里，我们进行等位基因交换，分别产生J2315和K56-2的等基因非色素和色素菌株，并对这些进行了测试，以确定pyomelanin是否在体外以及在体内CGD小鼠中对氧化应激的保护作用。我们的结果表明，改变的色素表型不会显著影响这些菌株抵抗体外H2O2和NO氧化应激的能力，也不会改变CGD小鼠体内的毒力和感染结果，这表明除了pyomelanin之外的其他因素也有助于这些菌株的病理生理学。伯克霍尔德氏菌（Bcc）是一组革兰氏阴性机会性细菌，通常与免疫力受损患者的致命肺部感染有关，特别是那些囊性纤维化和慢性肉芽肿病（CGD）。已知一些Bcc菌株天然产生pyomelanin，一种棕色黑色素样色素，已知能清除自由基并克服宿主细胞的氧化爆发。我们研究了pyomelanin在伯克霍尔德氏菌J2315（色素）和K56-2（非色素）中的作用，并进行了等位基因交换以产生等基因的非色素和色素菌株，分别。我们的结果表明，改变的色素表型不会显着影响这些菌株在体外抵抗H2O2或NO的能力，并且不会改变CGD小鼠体内呼吸道感染的结果。这些结果表明，pyomelanin可能并不总是构成毒力因子，并表明其他特征也有助于这些菌株的病理生理学。
