Weiser J N, Markiewicz Z, Tuomanen E I, Wani J H
Department of Pediatrics, Children's Hospital of Philadelphia, Pennsylvania, USA.
Infect Immun. 1996 Jun;64(6):2240-5. doi: 10.1128/iai.64.6.2240-2245.1996.
Streptococcus pneumoniae undergoes phase variation in colony morphology, which has been implicated as a factor in the pathogenesis of pneumococcal disease. Phenotypic differences between opaque and transparent colony forms correlate with differences in rates of autolysis. This study examined whether differences in autolysis are caused by differences in expression of the major amidase, LytA, or the structure of its peptidoglycan substrate. No significant difference was detected by high-pressure liquid chromatography analysis of stem peptides released after treatment of purified peptidoglycan with amidase. Differences in the rate of digestion of purified cell walls, furthermore, did not correlate with susceptibility to autolysis. Lower levels of autolysis in opaque variants, however, was associated with decreased levels of immunodetectable LytA on colony immunoblots and Western blots (immunoblots). Diminished cell-surface-associated LytA in opaque variants was also demonstrated by whole-cell inhibition enzyme-linked immunosorbent assay. Since transparent variants have been shown both to colonize the nasopharynx more efficiently in an animal model and to express more surface-exposed LytA, it was determined whether LytA contributes to colonization in a neonatal rat model of pneumococcal carriage. Defined mutants in the lytA gene were used to show that there was no significant contribution by LytA to nasopharyngeal colonization in this model. Although the expression of LytA was shown to undergo phase variation in association with colony morphology, lytA mutants are still capable of phenotypic variation in colony morphology, which suggests that other factors are responsible for intrastrain differences which affect colonization.
肺炎链球菌的菌落形态会发生相变，这被认为是肺炎球菌疾病发病机制中的一个因素。不透明和透明菌落形式之间的表型差异与自溶速率的差异相关。本研究探讨了自溶差异是否由主要酰胺酶LytA的表达差异或其肽聚糖底物的结构差异引起。用酰胺酶处理纯化的肽聚糖后释放的茎肽经高压液相色谱分析未检测到显著差异。此外，纯化细胞壁的消化速率差异与自溶敏感性无关。然而，不透明变体中较低的自溶水平与菌落免疫印迹和蛋白质免疫印迹（免疫印迹）上免疫可检测的LytA水平降低有关。全细胞抑制酶联免疫吸附测定也证实了不透明变体中细胞表面相关LytA的减少。由于透明变体在动物模型中已被证明能更有效地定殖于鼻咽部且表达更多表面暴露的LytA，因此在肺炎球菌携带的新生大鼠模型中确定了LytA是否有助于定殖。lytA基因的特定突变体用于表明在该模型中LytA对鼻咽定殖没有显著贡献。尽管已证明LytA的表达会随着菌落形态发生相变，但lytA突变体在菌落形态上仍能发生表型变异，这表明其他因素是影响定殖的菌株内差异的原因。
