Preparation of Antibiotic Stock Solutions and Discs

Last updated on May 30th, 2021

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.

About Acharya Tankeshwar 473 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.