Preparation of Antibiotic Stock Solutions and Discs

Preparation of antibiotic stock solutions

Antibiotics may be received as powders or tablets. It is recommended to obtain pure antibiotics from commercial sources, and not use injectable solutions.

Powders must be accurately weighed and dissolved in the appropriate diluents to yield the required concentration, using sterile glassware.

Standard strains of stock cultures should be used to evaluate the antibiotic stock solution. If satisfactory, the stock can be aliquoted in 5 ml volumes and frozen at -20ºC or -60ºC.

Stock solutions are prepared using the formula (1000/P) X V X C=W, where

  1. P= potency of the antibiotic base,
  2. V=volume in ml required,
  3. C=final concentration of solution and
  4. W=weight of the antimicrobial to be dissolved in V.

Preparation of dried filter paper discs

Whatman filter paper no. 1 is used to prepare discs approximately 6 mm in diameter, which are placed in a Petri dish and sterilized in a hot air oven. Dispense 0.005 ml (5 microliter) of antibiotic solultion using sterile micropipette tips.


iGEM. (n.d.). Antibiotic Stock Preparation.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

8 thoughts on “Preparation of Antibiotic Stock Solutions and Discs

  1. So except for the hot air oven sterilization, which other effective methods can be used to sterilize the filter paper disc?

  2. sir i want to check inhibition of S.aureus by using Alovera plant, but i am confused how to make antibiotic discs from Alovera at home.
    Plz gauid me sir
    waiting for kind reply.

  3. Dear Associate Professor Tankeshwar,

    I would like to inquire on the the ready made antibiotic sensitivity test disk ordered online.
    The disks come with antibiotics tablet and if you can advise if I have the disk are already impregnated with antibiotics or should I dilute it and reinoculate on the disks?

    A small protocol would be grateful.


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