Bacteriostatic and Bacteriocidal concentration

Hello lovelies.

Staph here.

Today we are discussing about Minimum inhibitory concentration (MIC)

We know two types of them:

1. Static - concentration at which the multiplication of the micro - organisms is inhibited.
2. Cidal - concentration at which the micro - organisms are killed.

Let's have a detailed look at them.

What is MIC?

MIC can be defined as the minimum concentration of any antibiotic or some nutritional component (Salt, sugar, etc) which inhibits the microbial growth, either temporary or permanent.

Why is MIC carried out?

Of course, to determine that particular concentration which is able to inhibit the microbes. Especially when using a an antibiotic, the concentration should not be lower as it can cause development of resistance in the microbes, whereas high concentration can result in harmful side effects to the individual.

Same is the case for nutritional components. The concentration of the of the component should be enough to support the growth of micro - organisms. But a high concentration can inhibit the growth of micro - organisms. 

The best example I can quote here is the MIC of sugar and alcohol that we did during the wine fermentation.

How is MIC determined?

Serial or jumping dilutions of the antibiotic (or any xyz component whose MIC is needed to be determined) is carried out. 

A loopful or 0.1 ml of the culture is added to the tubes and incubated overnight. Positive and negative controls are also made.

After incubation, the tubes are compared with the controls and the first tube which shows absence of growth is noted as the MIC.

What is the difference between Bacteriostatic and Bactericidal concentrations and how to identify them?

As mentioned above bacteriostatic concentration inhibits the growth of the micro - organisms temporarily, whereas bactericidal concentration permanently kills them. 

Now, the main question is, the tube which showed no growth had static concentration or the cidal, right?

The answer is simple. Just streak a nutritionally complete medium with loopful of the media from the same tube.

Post incubation, if you observe growth on the plate then the concentration in the tube is bacteriostatic.

And if you see no growth after incubation, then the concentration in the tube is surely bactericidal.

Phew, I guess we are done.

Ask me any questions if you have or any suggestions that you want to give.

Lots of love, high six.

-Staph :D