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In vitro, whole-cell, inhibition assays in rich media vs. other media

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The assays that I have in mind are disk diffusion assays and assays to determine minimum inhibitory concentration or related.  Sometimes these assays are conducted in rich medium (Luria broth, Terrific Broth, or similar).  It seems to me that this choice biases against finding inhibitors that target enzymes whose absence is conditionally lethal.  If one inhibits an enzyme that produces a metabolite that can be obtained from the medium, then growth of the cells might be impaired little or not at all.  If one is interested in developing an antimicrobial compound, perhaps using a medium that mimics human serum is a better choice, but I imagine that there are complications  I doubt very much that I am the only person who has wondered about this possible problem.  Are there any papers that touch upon this subject or address it in a systematic manner.

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  • 3 weeks later...

Off the top of my head I don't know specific papers, but this is a somewhat known but in clinical practice also somewhat ignored issue. You are right that the medium choice will affect outcome and it goes beyond issues such as auxotrophic effects. It is close to something that my group is working on, but ultimately one has to recognize that clinical practice is driven by pragmatism. I.e. standard media are used because they are (for the most part) informative and allow direct comparisons.

If one wants to understand cellular resilience against ABs, things get exponentially more complicated (as even different strain can have different metabolic adaptations that can change their susceptibility to a large degree). And you can complicate it further as the growth history can play a role. I.e. cells grown under nutrient replete or deplete conditions and then exposed to AB under certain conditions can be more or less susceptible, too. This is basically why these assays are run under standard conditions to mostly eliminate (or ignore) these issues, allowing a simplified characterization. 

If wondering from a microbial perspective there are different areas to look into, all of which are unresolved. These includes stress generation and how cells deal with it when exposed to AB (oxidative stress was a assumed to be a main hub, but I have a slightly different view on that matter) and increasingly, metabolic diversion and flexibility. An example is given here, but it is important to note that these effects are not universal. Using a different bacterial species you do see quite different outcomes.




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