From the point of view of microbiology, for specific or physiological groups of microbes isolated or culturing from the soil, what is the type of medium being used, "selective medium" "semi-selective medium," or differential medium." and what is the difference among them?
A differential medium is one where you can differentiate among different types of bacteria, it usually is also partially selective. For example MacConkey medium has bile salts which selects against the growth of many types of bacteria, but also permits many types to grow. The lactose fermentation indicator further differentiates E. coli from other enteric Lac- bacteria that might be able to grow.
A selective medium is one where only your organism of choice grows, for example an antibiotic medium would only permit resistant strains to grow, or a minimal medium with lactose as sole carbon source would only permit Lac+ bacteria to grow. Semi-selective is sort of a vague term, but you could imagine the bile salts in MacConkey to be a semi-selective agent.
Phil Geis
https://www.google.com/search?q=semi-selective+medium&sxsrf=ALiCzsbmYOIo33k3tmPVVwZIfbKypogOPw%3A1665325597501&ei=HdpCY835FeuF9u8P6K69CA&ved=0ahUKEwiN_KmlrdP6AhXrgv0HHWhXDwEQ4dUDCA4&uact=5&oq=semi-selective+medium&gs_lp=Egdnd3Mtd2l6uAED-AEBMgQQABgewgIHEAAYHhiwA5AGAUjEDFCNBliNBnABeADIAQCQAQCYAaABoAGgAaoBAzAuMeIDBCBBGAHiAwQgRhgAiAYB&sclient=gws-wiz
Phil Geis I think the definition breaks down if you are talking about a pure culture of organism, then I agree the media is selective or not. But if you are talking about working with a natural sample of some sort that has a mixture of organisms, it makes more sense that it restricts growth to a limited subset of organisms but not to a unique one, for example a medium with bile salts primarily permits enteric bacteria to grow and limits the growth of many other bacteria, but does not select for any specific enteric.
Michael J. Benedik
Thanks Michael. Don't think one needs selective media for pure culture and restricting growth to limited subset is just what you have with a selective medium. I've not heard of MacConkey or EMB termed "semi-selective".
Think we're trying to contrive a definition for a term casually used by a few authors.
What semi-selective, it's not far different from selective media...the best you have is to use selective media when you need to get a specific microbial species because it saves time, money and effort.
According to Sigma-Aldrich company, « enriched media, on the other hand, are semi-selective: they contain supplements such as blood, serum, and egg yolk to enhance the growth of fastidious bacteria among the undemanding ones also present. While enriched media usually come in agar plates, enrichment media are for liquid cultivation. These media also favor the growth of a particular microorganism over others in a sample. Enrichment is often performed to have enough material of an organism available for subsequent detection, isolation, and/or identification. »
Here is the web link for reference.
Types of Media in Microbiology (sigmaaldrich.com)
Thanks Guy - pedantic contrivance.
Enrichment is semi-selective? That they allow growth of fastidious bacteria AS WELL AS the "undemanding" is selective? The supplements do not inhibit.
By extension, every medium is "semi-selective" or just selective - every ingredient allows some microbial additional growth over what you'd see with just distilled water and selective is every medium - favoring culturable vs noncontrollable, aerobic incubation favoring aerobes and facultative anaerobes, most media inhibiting extremophiles, xerophiles, ......
The term "semi - selective" was rarely used however, selective medium is containing ingredients that inhibit the growth of Microorganisms other than the desired and allowed the growth of desired microbes. Eosin methylene blue agar, Mannitol salt agar are examples of selective media. In the case of semi selective, I saw publication by Kossi et al, (2019) where he used additional ingredients such as NaCl to grow Pantoea strains
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