Assessment of a New Antibiotic.

 

Introduction:

• Antimicrobial Resistance (AMR) is a way through which microbes change their ways through which a particular antibiotic is acting on them making it ineffective.

• The AMR is giving rise to tougher microbial strains, some of them are even resistant to all the antibiotics available today we call such stains as superbugs.

• If new antibiotics are not introduced, the patients will die due to the previously treatable infections.

• The antibiotics are assessed in many ways like their efficiency, side effects, health gains, spectrum etc.

• Minimum Inhibitory Concentration is a one of criteria that establishes efficiency of an antibiotic.

• Minimum Inhibitory Concentration is the minimum concentration at which an antibiotic inhibits the growth of microorganism but not necessarily kills it.

• MIC the term is applicable to antibiotics, disinfectants, antiseptics and preservatives.

• MIC of an antibiotic is tested either by one of the following ways,

• Liquid Dilution Method.

• Solid Dilution Method.

Liquid Dilution Method (Test Tube Method)

• Twelve test tubes are taken and are labelled as per table 1.1.

Tube Number	Volume of Double Strength Medium (ml)	Volume of Test Chemical (ml)	Volume of Sterile Water (ml)
0 (Uninoculated)	5	0.0	5
0 (Control)	5	0.0	5
1	5	0.5	4.5
2	5	1.0	4.0
3	5	1.5	3.5
4	5	2.0	3.0
5	5	2.5	2.5
6	5	3.0	2.0
7	5	3.5	1.5
8	5	4.0	1.0
9	5	4.5	0.5
10	5	5.0	0.0

• Double strength medium is added in all test tubes.

• First test tube (Uninoculated) inoculum is not added and is used to check sterility of the medium used.

• In all other remaining eleven test tubes 3-4 drops of inoculum is added to reach 105-106 cells/ ml concentration of the test microorganism.

• In all test tubes except “Uninoculated” and “Control” chemical agent under test are added from 0.5 ml to 5.0 ml.

• The final volume of 10 ml is adjusted using sterile water in all test tubes.

• Contents of all test tubes are mixed well and incubated @ 37℃ for 2-3 days.

• After incubation all tests tubes are examined for growth of microorganism and the minimum inhibitory concentration is calculated.

• It is necessary to carry out a preliminary experiment to determine the range of MIC of the chemical agent under test.

Solid Dilution Method:

• In this method the chemical agent under test is mixed in the molten agar and then is poured in the petri dish.

• After solidification, the inoculum is spread on the surface of the agar medium.

• All the plates are incubated @ 37℃ for 2-3 days.

• After incubation all petri dishes are examined for growth of microorganism and the minimum inhibitory concentration is calculated.

Advantages:

1. Several microorganisms can be studied once by using a multipoint inoculator.

2. Contaminations can easily be detected as colony features are distinctive here rather than turbidity difference.