Attempts to estimate total numbers of eubacteria and archae bacteria are problematic because of difficulties such as detection in and recovery from the environment. As indicated earlier, estimates indicate that the numbers of unculturable microbial taxa greatly exceed those of the culturable organisms. Recent estimates suggest that the number of bacterial species in the world is between 10⁷ and 10⁹. Until very recently, microbial identification required the isolation of pure cultures followed by testing for multiple physiologic and biochemical traits. Clinicians have long been aware of human diseases that are associated with visible but nonculturable microorganisms. Scientists are now using a PCR-assisted approach using rRNA as a tar get to identify pathogenic microorganisms in situ. The first phase of this approach involves the extraction of DNA from a suitable specimen, the PCR amplification of the ribosomal DNA, the sequencing of the rRNA sequence information, and a comparative analysis of the retrieved sequences. This yields information on the identity or relatedness of the sequences in comparison with the available database. This approach has been used in the identification of pathogenic microorganisms. For example, a previously uncharacterized pathogen has been identified as the Whipple-disease–associated rod-shaped bacterium now designated Tropheryma whipplei. This rRNA approach has also been used to identify the etiologic agent of bacillary angiomatosis as Bartonella henselae and to show that the opportunistic pathogen Pneumocystis jiroveci is a member of the fungi. Undoubtedly, these and other techniques will identify additional etiologic agents in the future.

مواضيع ذات صلة

Heinz body preparation

Haptoglobin

Transthyretin (Prealbumin)

 C-reactive protein

growth hormone (GH,Human growth hormone [HGH],Somatotropin hormone [SH])

glycosylated hemoglobin (GHb, GHB, Glycohemoglobin, Glycolated hemoglobin, Hemoglobin [Hb A1c ], Diabetic control index)

Cultivation of Streptococcus, Enterococcus, and Similar Organisms

Direct Detection Methods of Streptococcus, Enterococcus, and Similar Organisms

Immunoglobulins

Complement

Ceruloplasmin

glucose tolerance test (GTT, Oral glucose tolerance test [OGTT])