Composition Of The Adult Fecal Microbiota Assessed By Molecular Techniques

With the advent of molecular-based techniques, bacterial characterization has become much more accurate, since it no longer relies upon phenotypic traits (which often vary due to the elastic nature of bacterial growth). In addition, more direct comparisons can be made between laboratories and across different studies. Initial work employed molecular methods to identify and/or discriminate different bacterial isolates from cultivation studies. One such study demonstrated that the majority of bacterial isolates from six healthy humans belonged to either the Bact. fragilis group or the Clostridium coccoides group (53). Bifidobacterium, the Clostridium leptum subgroup, Collinsella and Prevotella were also shown to be common phylogenetic lineages represented in healthy humans. Recent developments in molecular biology afford not only accurate and reproducible identification techniques for microbial isolates, but also strategies for direct community analysis at a number of genetic levels. Improved understanding of microbial taxonomy has generated a wealth of probing and polymerase chain reaction (PCR)-based strategies for quantification and/or qualification studies. Community profiling assays, including denaturing gradient gel electrophoresis (DGGE) and sequencing of clonal libraries from GI samples, have revolutionized our knowledge of the microbial composition of the GI tract.

The development and application of PCR-based methods and probing strategies, which have circumvented cultivation, highlighted the "tip-of-the-iceberg" scenario that our knowledge of the GI tract microbiota amounted to. The coverage that cultivation studies afforded has been calculated to be as low as 10%, although others suggest it may be as high as 40-58% (15,54-56). Modern cultivation media and incubation conditions enable greater diversity, and therefore coverage, to be recognized. However, many components of the human gut microbiota remain elusive to cultivation in vitro. Molecular strategies also have their limitations, including detection limits and inherent biasing. As such, the overall objective of the study generally determines which assay is most appropriate. In the case of investigations to elucidate the diversity and dynamics of the human gut microbiota, a polyphasic approach is best, allowing thorough analysis at multiple taxonomic levels.

Pregnancy And Childbirth

Pregnancy And Childbirth

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