Generally a nutrient agar broth when freshly prepared is transparent in looks. with inoculation of bacteria the solution becomes turbid over time and the change in turbidity can be measured in a spectrophotometer. However when a bactericide solution is added the turbidity keeps on decreasing over time as indicated by spectrophotometer. I have also observed this in many literature tables. Turbidity is however a physical phenomenon. once a solution becomes turbid how is it possible for a bactericide to make the turbidity disappear. what is the chemical reaction involved in this?
Dear Kamesh,
In terms of a bacterial solution, turbidity means optical density of bacterial cells. As bacteria divide and grow, they populate the broth and hence the broth looks turbid. When you add something that kills the bacteria, their cells burst open and hence the solution looks clear again.
Technically : living cells suspended in media, diffuse light rays more than the media itself.
Bacterial solution where the bacterial cells are intact will be turbid. When you do lysis of the bacterial cells, the cell walls break open and the contents are released in to the medium reducing the turbidity. This will be clearly seen when we do plasmid isolation from the overnight grown bacterial cells. We pellet the bacteria and resuspend them in the resuspension solution during which the solution will be turbid. Once we add lysis buffer/ Alkaline solution such as NaOH the resuspended bacterial solution will become perfectly clear with little mixing with in few seconds. I suggest you to do plasmid extraction and you will witness the answer for your question.
See The turbidity is just because of the bacterial cells as mentioned by other researchers.
Technically when you add any bactericidal solution it depends on the nature of bactericide what will happen in the broth. For example if the bactericidal solution turns the broth into a hypertonic solution then the bacterial cells will be ruptured because of the hypertonicity, and the broth may become even more turbid.
If the bactericidal solution is some kind of antibiotic that kills the bacteria by the means of inhibiting PS or other mechanisms even then the turbidity will remain same. Once the bacterial cells are killed in the broth they will settle down in the bottom resulting a clearer solution in the upper region of the container, actually the solution has not become clearer.
Yes adding alkali solution will make the solution clear but it depends on the nature of bactericidal solution
Abhishek Sen, Dr.Sesha Kiran Kollipara what about if we didn't add bactericide to the solution? will the solution remains it turbidity or the solution of the broth will be cleared as well?
Mohd Nasharudin ,
Your question is not clear, at least not to me. If you don't add any bactericidal solution post your fermentation run the turbidity will keep on reducing as the cells will die due to nutrient depletion(provided you are not feeding them at the same time. )/ ageing.
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