Department of Bacteriology and Immunology, Norwegian Institute of Public Health, Oslo, Norway.
Laboratory of Pediatric Infectious Diseases, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Microbiology (Reading). 2010 Mar;156(Pt 3):838-848. doi: 10.1099/mic.0.035345-0. Epub 2009 Dec 3.
Accurate differentiation between pneumococci and other viridans streptococci is essential given their differences in clinical significance. However, classical phenotypic tests are often inconclusive, and many examples of atypical reactions have been reported. In this study, we applied various phenotypic and genotypic methods to discriminate between a collection of 12 streptococci isolated from the upper respiratory tract of HIV-seropositive individuals in 1998 and 1999. Conventional phenotypic characterization initially classified these streptococci as Streptococcus pneumoniae, as they were all sensitive to optochin and were all bile soluble. However, they did not agglutinate with anti-pneumococcal capsular antibodies and were also far more resistant to antimicrobial agents than typeable pneumococci isolated in the same period. Genotypic characterization of these isolates and control isolates by both multilocus sequence analysis (MLSA) and comparative genomic hybridization (CGH) showed that only a single isolate was genetically considered to be a true S. pneumoniae isolate, and that the remaining 11 non-typable isolates were indeed distinct from true pneumococci. Of these, 10 most closely resembled a subgroup of Streptococcus mitis isolates genetically, while one strain was identified as a Streptococcus pseudopneumoniae isolate. CGH also showed that a considerable part of the proposed pneumococcal core genome, including many of the known pneumococcal virulence factors, was conserved in the non-typable isolates. Sequencing of part of the 16S rRNA gene and investigation for the presence of ply by PCR corroborated these results. In conclusion, our findings confirm the close relationship between streptococci of the Mitis group, and show that both MLSA and CGH enable pneumococci to be distinguished from other Mitis group streptococci.
鉴于肺炎球菌和其他草绿色链球菌在临床意义上的差异，准确地区分两者至关重要。然而，经典的表型测试往往不能得出明确的结论，并且已经报道了许多非典型反应的例子。在这项研究中，我们应用了各种表型和基因型方法来区分 1998 年和 1999 年从艾滋病毒血清阳性个体的上呼吸道分离出的 12 株链球菌。最初，常规表型特征将这些链球菌分类为肺炎链球菌，因为它们对 Optochin 均敏感，且均能溶解于胆汁。然而，它们与抗肺炎球菌荚膜抗体不凝集，并且与同期分离的可分型肺炎球菌相比，对抗菌药物的耐药性也高得多。通过多位点序列分析（MLSA）和比较基因组杂交（CGH）对这些分离株和对照分离株的基因型特征进行分析表明，只有一个分离株在遗传上被认为是真正的肺炎链球菌分离株，其余 11 个不可分型的分离株确实与真正的肺炎球菌不同。其中，10 个与遗传上最接近的是米氏链球菌亚群，而一个菌株被鉴定为肺炎链球菌分离株。CGH 还表明，非分型分离株中保守了相当一部分拟议的肺炎球菌核心基因组，包括许多已知的肺炎球菌毒力因子。16S rRNA 基因部分序列测定和 ply 存在情况的 PCR 检测结果证实了这些结果。总之，我们的研究结果证实了米氏链球菌与链球菌之间的密切关系，并且表明 MLSA 和 CGH 均能将肺炎球菌与其他米氏链球菌区分开来。
