We found that at the same concentration of a medium-chain free fatty acid, it had a poor inhibitory effect on high concentrations of bacteria and a high inhibitory effect on low concentrations of bacteria.
Can it be explained with some theory and principle?
Might some study you recommend to support or rebut it?
Thank for your attention.
Your experimental observation is not unexpected. The size of the inoculum is one of the factors affecting the effectiveness of an antimicrobial compound. Also, the essence of inoculum standardization is to help establish the spectrum of the antimicrobial's activity. An analogy could be drawn from the general knowledge of chemistry: when the the number of moles between two reactants is tipped in favour of one of the reacting species, a stage is attained when such increase does not result in increase in product formation, because the reactant with a fewer number of free reacting molecules is saturated.
Hi Wang Lu,
I think here you would have done some antimicrobial assays like, MIC or MBC. Therefore, I would like to suggests you to maintain your concentration of bacteria (which is you're using) as constant in the test instead of applying some variability. Because, here you need to seek the minimum inhibitory or minimum bacteriocidal concentration of the used compound, like you're using medium chain fatty acids, and you can change its concentration according to the Dilution factor. If you will variate your bacterial concentration, then the optimum concentration of the antimicrobial compound can't be achieved adequately (variability of bacterial concentration may cause hindrance in the activity of your compound). Antimicrobial Fatty acids generally affects the Bacterial cell membrane by component exchange like phospholipids with cell membrane which ultimately causes osmotic imbalance.
In your case, I think during high concentration of the bacteria the action of compound is getting affected due to its inappropriate distribution to the bacterial cells. And when you're using low bacteria concentration in respective to the optimum compound distribution, then inhibitory effect gets increased. Likely to be in this way, your results are getting fluctuated.
I hope this will clear some of your doubts.
Thank you,
Regards.
Your experimental observation is not unexpected. The size of the inoculum is one of the factors affecting the effectiveness of an antimicrobial compound. Also, the essence of inoculum standardization is to help establish the spectrum of the antimicrobial's activity. An analogy could be drawn from the general knowledge of chemistry: when the the number of moles between two reactants is tipped in favour of one of the reacting species, a stage is attained when such increase does not result in increase in product formation, because the reactant with a fewer number of free reacting molecules is saturated.
As it has been said before, the relative concentration of antimicrobial vs bacteria is important and the less bacterial density, the more antimicrobial per cell there will be. Furthermore it is important to remember that bacterial cultures experience significant physiological and expression changes over the course of their growth curves and many resistance mechanisms are regulated by quorum sensing mechanisms that only trigger after a critical bacterial density is reached.
While the acid nature of the fatty acids will have some inhibitory effect on growth, the high population is mostly likely to have a greater enzymatic breakdown of the FA's and their ability to be inhibitory.
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