Boucher J C, Yu H, Mudd M H, Deretic V
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.
Infect Immun. 1997 Sep;65(9):3838-46. doi: 10.1128/iai.65.9.3838-3846.1997.
A distinguishing feature of Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients is their mucoid, exopolysaccharide alginate-overproducing phenotype. One mechanism of conversion to mucoidy is based on mutations in the algU mucABCD cluster, encoding the stress sigma factor AlgU and its regulators. However, conversion to mucoidy in laboratory strains can be achieved via mutations in other chromosomal sites. Here, we investigated mechanisms of the emergence of mucoid P. aeruginosa in CF by analyzing the status of mucA in a collection of mucoid P. aeruginosa isolates from 53 CF patients. This negative regulator of algU, when inactivated under laboratory conditions, causes conversion to mucoidy. The overall frequency of mucA alterations in mucoid CF isolates was 84%. Nucleotide sequence analyses revealed that the majority of the alterations caused premature termination of the mucA coding sequence. Comparison of paired nonmucoid and mucoid P. aeruginosa isolates from three CF patients indicated the presence of mucA mutations only in the mucoid strains. Interestingly, mucoid P. aeruginosa isolates from urinary tract infections also had mutations in the mucA gene. Clearance of CF isolates from the murine lung was investigated in an aerosol infection model with C57BL/6J, BALB/c, and DBA/2NHsd mice. Two CF strains, selected for further study based on the dependence of their alginate production on the concentration of salt in the medium, were used to examine the effects of mucoidy on pulmonary clearance. Statistically significant improvement in recovery from the murine lung of viable mucoid P. aeruginosa cells relative to the nonmucoid bacteria was observed in the majority of mouse strains tested. Collectively, the results reported here suggest that mucA is most likely the preferential site for conversion to mucoidy in CF and that alginate overproduction in mucA-mutant P. aeruginosa improves its resistance to the innate clearance mechanisms in the lung.
囊性纤维化（CF）患者分离出的铜绿假单胞菌菌株的一个显著特征是其黏液样、过量产生胞外多糖藻酸盐的表型。转化为黏液样的一种机制基于编码应激σ因子AlgU及其调节因子的algU mucABCD基因簇中的突变。然而，实验室菌株中转化为黏液样可通过其他染色体位点的突变实现。在此，我们通过分析来自53例CF患者的黏液样铜绿假单胞菌分离株中mucA的状态，研究了CF中黏液样铜绿假单胞菌出现的机制。algU的这种负调节因子在实验室条件下失活时会导致转化为黏液样。黏液样CF分离株中mucA改变的总体频率为84%。核苷酸序列分析显示，大多数改变导致mucA编码序列提前终止。对来自3例CF患者的配对非黏液样和黏液样铜绿假单胞菌分离株的比较表明，仅黏液样菌株中存在mucA突变。有趣的是，尿路感染的黏液样铜绿假单胞菌分离株中mucA基因也有突变。在C57BL/6J、BALB/c和DBA/2NHsd小鼠的气溶胶感染模型中研究了CF分离株从鼠肺中的清除情况。基于其藻酸盐产生对培养基中盐浓度的依赖性选择了2株CF菌株用于进一步研究，以检验黏液样对肺部清除的影响。在大多数测试的小鼠品系中，相对于非黏液样细菌，从鼠肺中回收的活黏液样铜绿假单胞菌细胞在统计学上有显著改善。总体而言，此处报道的结果表明，mucA很可能是CF中转化为黏液样的优先位点，并且mucA突变的铜绿假单胞菌中藻酸盐的过量产生提高了其对肺中固有清除机制的抗性。
