The document discusses the microbiological assay of antibiotics, which quantitatively estimates antibiotics by measuring their ability to inhibit the growth of microorganisms. There are two main methods - the cylinder-plate method which measures zones of inhibition, and the turbidimetric method which compares the turbidity of bacterial solutions with different antibiotic concentrations. The assay is useful for demonstrating antibiotic efficacy, detecting subtle molecular changes, and resolving doubts about antibiotic potency changes.

1. Microbiological Assay of Antibiotics

2. WHAT IS ANTIBIOTIC?
A medicine that-
Inhibits the growth of bacteria
Or destroys microorganisms

3. WHAT IS MICROBIOLOGICAL ASSAY?
Quantitative estimation of any antimicrobial agent.

4. MICROBIOLOGICAL ASSAY OF ANTIBIOTICS
Inhibition of growth of
micro-organisms by
measured
concentrations of the
antibiotics
Effect that produced by
known concentration of
a standard preparation
of the antibiotic having
a known activity.
Comparison between

5. METHODS
Two general method are usually employed:-
The cylinder-plate(or cup-
plate)method
The turbidimetric(or tube
assay)method

6. STEPS
Preparation of
media
Preparation
buffer
solutions
Preparation of
the standard
solution
Preparetion
test organisms

7. Take bacterial
sample
Take petri dish with
media sample
Transfer bacterial
sample in the media
Perforation in media
sample
Use different
antibiotics in the
cavity
Place in the
inoculation chamber
Measure zone of
inhibition

9. TURBIDIMETRIC METHOD
Bacteria with nutrient medium
Take 5 different concentration of standard and
sample concentration antibiotics
Take 1ml of standard and sample concentration of
antibiotics in different test tubes
Add 9ml of bacteria with nutrient medium solution
in each tubes
Compared turbidity

11. WHAY MICROBIOLOGICAL ASSAY OF ANTIBIOTICS?
The inhibition of growth may be utilized for
demonstrating the therapeutic efficacy of antibiotics.
Any subtle change in the antibiotic molecule which
may not be detected by chemical methods will be
revealed by a change in the antimicrobial activity.
Resolving doubts regarding possible change in
potency of antibiotics and their preparations.