Division of Infectious Diseases, Department of Medicine, University at Buffalo, State University of New York, Buffalo, NY 14203, USA.
BMC Microbiol. 2011 Aug 16;11:183. doi: 10.1186/1471-2180-11-183.
Nontypeable Haemophilus influenzae is a common cause of otitis media in children and lower respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). Prior studies have shown that H. influenzae expresses abundant urease during growth in the middle ear of the chinchilla and in pooled human sputum, suggesting that expression of urease is important for colonization and infection in the hostile environments of the middle ear and in the airways in adults. Virtually nothing else is known about the urease of H. influenzae, which was characterized in the present study.
Analysis by reverse transcriptase PCR revealed that the ure gene cluster is expressed as a single transcript. Knockout mutants of a urease structural gene (ureC) and of the entire ure operon demonstrated no detectable urease activity indicating that this operon is the only one encoding an active urease. The ure operon is present in all strains tested, including clinical isolates from otitis media and COPD. Urease activity decreased as nitrogen availability increased. To test the hypothesis that urease is expressed during human infection, purified recombinant urease C was used in ELISA with pre acquisition and post infection serum from adults with COPD who experienced infections caused by H. influenzae. A total of 28% of patients developed new antibodies following infection indicating that H. influenzae expresses urease during airway infection. Bacterial viability assays performed at varying pH indicate that urease mediates survival of H. influenzae in an acid environment.
The H. influenzae genome contains a single urease operon that mediates urease expression and that is present in all clinical isolates tested. Nitrogen availability is a determinant of urease expression. H. influenzae expresses urease during human respiratory tract infection and urease is a target of the human antibody response. Expression of urease enhances viability in an acid environment. Taken together, these observations suggest that urease is important for survival and replication of H. influenzae in the human respiratory tract.
非典型流感嗜血杆菌是儿童中耳炎和慢性阻塞性肺疾病（COPD）成人下呼吸道感染的常见病因。先前的研究表明，流感嗜血杆菌在南美栗鼠中耳和 pooled 人痰中生长时会大量表达脲酶，这表明脲酶的表达对于在中耳的恶劣环境中和成人气道中的定植和感染很重要。目前，人们对流感嗜血杆菌的脲酶几乎一无所知，本研究对其进行了特征描述。
逆转录 PCR 分析表明，ure 基因簇作为一个单一的转录本表达。脲酶结构基因（ureC）和整个 ure 操纵子的敲除突变体均未检测到脲酶活性，表明该操纵子是唯一编码活性脲酶的基因。ure 操纵子存在于所有测试的菌株中，包括中耳炎和 COPD 的临床分离株。随着氮源可用性的增加，脲酶活性降低。为了验证脲酶在人类感染期间表达的假设，使用从患有 COPD 并经历流感嗜血杆菌感染的成年人获得的感染前和感染后血清，在 ELISA 中使用纯化的重组 ureC 进行了检测。共有 28%的患者在感染后产生了新的抗体，这表明流感嗜血杆菌在气道感染期间表达脲酶。在不同 pH 值下进行的细菌生存能力测定表明，脲酶介导了流感嗜血杆菌在酸性环境中的存活。
流感嗜血杆菌基因组包含一个单一的 ure 操纵子，该操纵子介导脲酶的表达，并且存在于所有测试的临床分离株中。氮源可用性是脲酶表达的决定因素。流感嗜血杆菌在人类呼吸道感染期间表达脲酶，并且脲酶是人体抗体反应的靶标。脲酶的表达增强了其在酸性环境中的生存能力。综上所述，这些观察结果表明，脲酶对于流感嗜血杆菌在人类呼吸道中的存活和复制很重要。
