Fastidious organism

A fastidious organism is any organism that has complex or particular nutritional requirements. In other words, a fastidious organism will only grow when specific nutrients are included in its diet. The more restrictive term fastidious microorganism is used in microbiology to describe microorganisms that will grow only if special nutrients are present in their culture medium. Thus fastidiousness is often practically defined as being difficult to culture, by any method yet tried. An example of a fastidious bacterium is Neisseria gonorrhoeae, which requires blood or hemoglobin and several amino acids and vitamins to grow. Other examples include Campylobacter spp. and Helicobacter spp., which are capnophilic – require elevated CO2 – among other requirements. Fastidious organisms are not inherently 'weak'—they can flourish and thrive in their particular ecological niche with its particular nutrients, temperature, and absence of competitors, and they can be quite difficult to kill off. But they are difficult to culture simply because it is difficult to accurately simulate their natural milieu in a culture medium. For example, Treponema pallidum is not easy to culture, and yet it is strong on its home turf, being rather difficult to eradicate 100% from all tissues of a person with syphilis. A fastidious organism is any organism that has complex or particular nutritional requirements. In other words, a fastidious organism will only grow when specific nutrients are included in its diet. The more restrictive term fastidious microorganism is used in microbiology to describe microorganisms that will grow only if special nutrients are present in their culture medium. Thus fastidiousness is often practically defined as being difficult to culture, by any method yet tried. An example of a fastidious bacterium is Neisseria gonorrhoeae, which requires blood or hemoglobin and several amino acids and vitamins to grow. Other examples include Campylobacter spp. and Helicobacter spp., which are capnophilic – require elevated CO2 – among other requirements. Fastidious organisms are not inherently 'weak'—they can flourish and thrive in their particular ecological niche with its particular nutrients, temperature, and absence of competitors, and they can be quite difficult to kill off. But they are difficult to culture simply because it is difficult to accurately simulate their natural milieu in a culture medium. For example, Treponema pallidum is not easy to culture, and yet it is strong on its home turf, being rather difficult to eradicate 100% from all tissues of a person with syphilis. An example of the practical relevance of fastidiousness is that a negative culture result could be a false negative; that is, just because culturing failed to produce the organism of interest does not mean that the organism was absent from either the sample, the place where the sample came from, or both. This means that the sensitivity of the test is less than perfect. So, for example, culture alone may not be enough to help a doctor trying to find out which bacteria is causing pneumonia or sepsis in a hospitalized patient, and therefore which antibiotic to use. When there is a need to determine which bacteria or fungi are present (in agriculture, medicine, or biotechnology), scientists can also turn to other tools besides cultures, such as nucleic acid tests (which instead detect that organism's DNA or RNA, even if only in fragments or spores as opposed to entire cells) or immunologic tests (which instead detect its antigens, even if only in fragments or spores as opposed to entire cells). The latter tests may be helpful in addition to (or instead of) culture, although circumspection is required in interpreting their results, too, because the DNA, RNA, and antigens of many different bacteria and fungi are often much more prevalent (in air, soil, water, and human bodies) than is popularly imagined—at least in tiny amounts. So a positive on those tests can sometimes be a false positive regarding the important distinction of infection versus just colonization or ungerminated spores. Such considerations are why skill is needed in deciding which test is appropriate to use in a given situation and in interpreting the results.