John James, Kasudhan Kripa Shanker, Kanungo Reba, Sharma Savitri, Dohe Vaishali, Prashanth K
Department of Biotechnology, School of Life Sciences, Pondicherry University, Puducherry, India.
Department of Biotechnology, School of Life Sciences, Pondicherry University, Puducherry; Department of Pharmacology, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
Indian J Med Microbiol. 2017 Oct-Dec;35(4):511-517. doi: 10.4103/ijmm.IJMM_17_183.
Streptococcus pneumoniae continues to cause morbidity and mortality across the globe, with developing countries bearing the brunt of the disease. It is mainly responsible for meningitis, pneumonia and septicaemia primarily in children, elderly and immunocompromised persons. Colonisation and persistence in the human nasopharynx occur during early childhood, and it appears to be prerequisite for invasive pneumococcal disease (IPD). Factors that help in persistent colonisation and subsequent invasion are ill understood. Several virulence factors have been incriminated for nasopharyngeal carriage (NC) as well as for the manifestation of the pathogenesis of IPD.
This study attempts to characterise the S. pneumoniae isolates through analysing the distribution of different virulence markers such as lytA, ply, pbpA, eno, psaA, amiA, ciaR and wchA among the isolates obtained from disease and NC. A total of 37 isolates which include 14 invasive and 23 non-invasive isolates were investigated by polymerase chain reaction to detect the genes. Eight representative isolates were investigated for mutations in wchA by DNA sequencing that may responsible for capsular variation.
Ply, pbpA, amiA and eno were observed in a greater percentage of invasive isolates than non-invasive isolates though these differences are not statistically significant. Other two genes ciaH and psaA did not show any significant difference between two groups of isolates. Biofilm production was significantly higher in than non-invasive isolates when compared to invasive isolates. Sequence analysis of wchA revealed three significant point mutations or single-nucleotide polymorphisms (SNPs) among the isolates of one particular cluster (cluster III). These SNPs are responsible for a non-synonymous mutation in wchA bringing in an amino acid change in WchA protein, which is a part of the capsule of S. pneumoniae. Notably, all the three isolates present in cluster III had these SNPs and all of them were isolated from ocular infections.
The results of our study implies a possible capsular variations among the isolates and this may have an impact on capsular typing.
肺炎链球菌在全球范围内持续导致发病和死亡，发展中国家首当其冲。它主要导致儿童、老年人和免疫功能低下者患脑膜炎、肺炎和败血症。肺炎链球菌在儿童早期定殖并持续存在于人类鼻咽部，这似乎是侵袭性肺炎球菌病（IPD）的先决条件。有助于持续定殖和随后侵袭的因素尚不清楚。几种毒力因子已被认为与鼻咽部携带（NC）以及IPD发病机制的表现有关。
本研究试图通过分析不同毒力标志物（如lytA、ply、pbpA、eno、psaA、amiA、ciaR和wchA）在疾病和NC分离株中的分布来鉴定肺炎链球菌分离株。通过聚合酶链反应对总共37株分离株（包括14株侵袭性分离株和23株非侵袭性分离株）进行基因检测。对8株代表性分离株进行DNA测序，以研究可能导致荚膜变异的wchA基因突变。
侵袭性分离株中ply、pbpA、amiA和eno的检出率高于非侵袭性分离株，尽管这些差异无统计学意义。另外两个基因ciaH和psaA在两组分离株之间未显示出任何显著差异。与侵袭性分离株相比，非侵袭性分离株的生物膜形成显著更高。wchA的序列分析显示，在一个特定簇（簇III）的分离株中有三个显著的点突变或单核苷酸多态性（SNP）。这些SNP导致wchA发生非同义突变，使肺炎链球菌荚膜的一部分WchA蛋白的氨基酸发生变化。值得注意的是，簇III中的所有三株分离株都有这些SNP，并且它们均从眼部感染中分离得到。
我们的研究结果表明分离株之间可能存在荚膜变异，这可能会对荚膜分型产生影响。
