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.

References

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