Ciofu Oana, Lee Baoleri, Johannesson Marie, Hermansen Nils Olav, Meyer Peter, Høiby Niels
Institute of International Health, Immunology and Microbiology, University of Copenhagen, Rigshospitalet, Copenhagen, Denmark.
Uppsala CF Center, Department of Women's and Children's Health, Uppsala University, Uppsala University Hospital, SE-75185 Uppsala, Sweden.
Microbiology (Reading). 2008 Jan;154(Pt 1):103-113. doi: 10.1099/mic.0.2007/010421-0.
Pseudomonas aeruginosa is the dominant pathogen causing chronic lung infections in patients with cystic fibrosis (CF). After an initial phase characterized by intermittent colonizations, a chronic infection is established upon conversion of P. aeruginosa from the non-mucoid to the mucoid, alginate-overproducing phenotype. During the chronic infection the isolation of both mucoid and non-mucoid isolates in CF sputum samples is very common. The purpose of the present study was to establish, by sequence analysis, the types of mutations present in the algTmucABD operon in a large number of mucoid and non-mucoid P. aeruginosa isolates from Scandinavian CF patients and in in vitro-derived non-mucoid revertants. Mucoid (83) and non-mucoid isolates (103) from 91 Scandinavian patients with chronic P. aeruginosa infection and 24 non-mucoid isolates from intermittently colonized CF patients were investigated. In addition, 88 spontaneous non-mucoid revertants obtained in vitro from nine mucoid CF isolates were also included in the study. Mutations in mucA were found in 92 % of the mucoid and in up to 70 % of the non-mucoid isolates from chronically infected patients, indicating that the majority of non-mucoid isolates are revertants. None of the non-mucoid isolates from intermittently colonized CF patients harboured mucA mutations. Although algT has been considered an important gene for secondary-site mutations responsible for reversion to non-mucoidy, only 30 % of the mucA-mutated non-mucoid CF isolates had mutations in algT. In contrast, 83 % of the in vitro-derived spontaneous non-mucoid revertants had mutations in algT, showing that in the CF lung there is a selection for non-mucoid revertants with secondary-site mutations in genes other than algT. In addition, we report, to our knowledge for the first time, loss-of-function mutations in the negative regulators mucB and mucD in CF clinical isolates. In some of the CF isolates these mutations are associated with moderate alginate production. In conclusion, most non-mucoid isolates from chronically infected CF patients are revertants and the mechanism of revertance is algT-independent in the CF lung.
铜绿假单胞菌是导致囊性纤维化（CF）患者慢性肺部感染的主要病原体。在以间歇性定植为特征的初始阶段之后，当铜绿假单胞菌从非黏液型转变为黏液型、产生过量藻酸盐的表型时，就会形成慢性感染。在慢性感染期间，CF痰液样本中同时分离出黏液型和非黏液型菌株是非常常见的。本研究的目的是通过序列分析，确定来自斯堪的纳维亚CF患者的大量黏液型和非黏液型铜绿假单胞菌分离株以及体外衍生的非黏液型回复株中algTmucABD操纵子存在的突变类型。对来自91例患有慢性铜绿假单胞菌感染的斯堪的纳维亚患者的黏液型（83株）和非黏液型分离株（103株）以及来自间歇性定植的CF患者的24株非黏液型分离株进行了研究。此外，从9株黏液型CF分离株体外获得的88株自发非黏液型回复株也纳入了本研究。在来自慢性感染患者的黏液型分离株中，92%发现了mucA突变，在非黏液型分离株中高达70%发现了mucA突变，这表明大多数非黏液型分离株是回复株。来自间歇性定植的CF患者的非黏液型分离株均未携带mucA突变。尽管algT被认为是导致回复为非黏液型的第二位点突变的重要基因，但只有30%的mucA突变的非黏液型CF分离株在algT中有突变。相比之下，83%的体外衍生的自发非黏液型回复株在algT中有突变，这表明在CF肺中存在对algT以外基因有第二位点突变的非黏液型回复株的选择。此外，据我们所知，我们首次报告了CF临床分离株中负调控因子mucB和mucD的功能丧失突变。在一些CF分离株中，这些突变与中度藻酸盐产生有关。总之，来自慢性感染CF患者的大多数非黏液型分离株是回复株，并且在CF肺中回复机制不依赖于algT。
