Streptococcus pneumonıae: Klasik ve moleküler tanıda karşılaşılan sorunlar

Streptococcus pneumoniae viridans grubu (Smit grubu, mitis grubu) streptokoklardandır; dolayısıyla grubun ortak özelliklerini taşır. Toplumda kazanılan pnömoni yanında çeşitli infeksiyonlara da yol açabilen kapsülsüz şekilleri üst solunum sisteminde viridans grubu bakterilerle beraber bulunur. Bu nedenle S.pneumoniae’nin atipik viridans grubu streptokoklardan (S.mitis, S.orilis, S.pseudopneumoniae) ve streptokok benzeri bakterilerden (Streptococcus-Like Bacteria) ayırd edilmesi gerekir. S.pseudopneumoniae son yıllarda tarif edilen, fenotipik ve genotipik özellikleri S.pneumoniae ve viridans grubu streptokoklardan farklı (kapsülsüz, optokine % 5 CO2’li ortamda dirençli veya orta duyarlı, normal atmosferde duyarlı, safrada erimeyen, AccuProbe DNA prob hibridizasyon testi pozitif) bir türdür. Pnömokokta tanı, klasik [optokine duyarlılık, safrada erime, serolojik yöntem (kapsül şişme deneyi, lateks aglutinasyonu)] ve moleküler yöntemlerle yapılır. Normalde steril vücut bölgelerinden izole edilen suşlarda klasik tanı genellikle yeterlidir. Ancak bakteri balgam gibi alt solunum sistemi örneklerinden izole edildiğinde suş optokine duyarlı olan, safrada eriyen viridans grubu atipik bir streptokok olabileceği gibi optokine dirençli, safrada erimeyen atipik bir pnömokok da olabilir. Viridans grubu bir streptokokun pnömokok özelliği göstermesi, o özelliği şifreleyen genlerin kazanılması sonucu ortaya çıkar. Dolayısıyla pnömokok tanısını sağlayan bazı genlerin şüpheli bakteride gösterilmesi o bakterinin her zaman pnömokok olduğunu göstermez. Bu durum moleküler göstergelerin de bazı suşlarda doğru sonuç vermediğini ortaya koymaktadır. Atipik pnömokoklar tanıda hedef alınan etki bölgesinin mutasyonu sonucu ortaya çıkar. Dolayısıyla atipik viridans grubu bir streptokokla, atipik pnömokoklar her zaman doğru olarak tanımlanamazlar. Yanlış bakteriyolojik tanı, yanlış klinik tanıya neden olacağından, tedavi başarısını etkileyen önemli bir faktördür. Bu tip hataları önlemek için klasik yöntemlerin yanında hızlı ve kesin sonuç verebilecek çeşitli moleküler yöntemler geliştirilmeye çalışılmış, ancak henüz altın standart bir yöntem bulunamamıştır.

Anahtar Kelimeler:

Moleküler tanı teknikleri, Streptococcus pneumoniae, Viridans streptokok

Streptococcus pneumoniae: Some problems in the conventional and molecular diagnosis

Streptococcus pneumoniae is a member of viridans group (the Smit group, streptococci of mitis group) streptoccoci and has the common characteristics of this group. The uncapsulated isolates may cause community acquired pneumoniae and many other infections, and exist together with the atypical viridans group streptococci in upper respiratory tract. Because of this, S.pneumoniae must be distinguished from atypical viridans group streptococci (S.mitis, S.oralis, S.pseudopneumoniae) and from Streptococcus-Like Bacteria. S.pseudopneumoniae which was described recently is a different species from S.pneumoniae and viridans group streptococci in terms of phenotypic and genotypic characteristics (unencapsulated, optochin resistant or intermediate in 5 % CO2 atmosphere but susceptible in normal atmosphere, insoluble in bile, AccuProbe DNA probe hybridization positive). The diagnosis of S.pneumoniae can be performed by classical [optochin susceptibility, bile solubility, serological methods (Quellung reaction, latex aglutination)] and molecular methods. For the identification of strains isolated from sterile regions of the body, the classical methods are generally sufficent. But the isolates from lower respiratory tract specimens may be optochin susceptible and bile soluble atypical viridans group strains or optochin resistant, bile insoluble atypical pneumococci. Viridans group streptococci may have the pneumococcal characteristics due to the acquisition of related genes. Thus, the existence of pneumococcus genes does not necessarily show that the strain is a pneumococcus. Because of this, the molecular methods are not always valid. Atypical pneumococci are appeared by the mutations in the targeted regions in the diagnosis. Because of atypical viridans group streptococci and atypical pneumococci, identification may be incorrect and incorrect identification can cause false clinical diagnosis effecting the treatment. To prevent the incorrect identification, besides classical methods, there are many studies to improve the molecular methods which give more accurate and reliable results but there is not still any gold standard method.

Keywords:

Molecular Diagnostic Techniques, Streptococcus pneumoniae, Viridans Streptococci,

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