Introduction

This is a reference sheet that provides name, concentration, and mode of action for common antibiotics used in molecular biology.

Antibiotics

Ampicillin

• Stock concentration. 4 mg/ml using sterile distilled water. Store at 4C.
• Working concentration. Add 12.5 ml of stock to 1 L of media to achieve a final concentration of 50 ug/ml (1:80).
• Mode of action. Bacteriocidal,  inhibiting formation of peptidoglycan cross-links in cell wall synthesis.

Carbenicillin

• Carbenicillin is directly interchangable with ampicillin. 
• Stock concentration. 4 mg/ml. Prepare with 50% ethanol/50% water and store at -20C.
• Working concentration. Add 12.5 ml of stock to 1 L of media to achieve a final concentration of 50 ug/ml (1:80).
• Mode of action. Bacteriocidal,  inhibiting formation of peptidoglycan cross-links in cell wall synthesis.

Chloramphenicol

• Stock concentration. 10 mg/ml. Prepare in methanol. Store at 4C.
• Working concentration. Add 2.0 ml of stock to 1 L of media to achieve a final concentration of 20 ug/ml (1:500).
• Mode of action. Bacteriostatic; inhibits protein synthesis by inhibiting peptidyltransferase associated with 50S ribososomal subunit

D-Cycloserine

• Stock concentration. 10 mg/ml. Prepare in 0.1 M sodium phosphate buffer, pH 8, just before use. Cycloserine solutions are unstable and should be made immediately before use.
• Working concentration. Add 20 ml of stock to 1 L of media to achieve a final concentration of 200 ug/ml (1:50).
• Mode of action. Bacteriocidal, inhibiting D-alanine production

Gentamycin

• Stock concentration. 10 mg/ml. Prepare using sterile distilled water . Store at 4C.
• Working concentration. Add 1.5 ml of stock to 1 L of media to achieve a final concentration of 15 ug/ml (1:667).
• Mode of action. Bacteriocidal, binding L6 subunit on the 50S ribosomal subunit.

Kanamycin

• Stock concentration. 10 mg/ml. Prepare using sterile distilled water . Store at 4C.
• Working concentration. Add 3.0 ml of stock to 1 L of media to achieve a final concentration of 30 ug/ml (1:333).
• Mode of action. Bacteriocidal, inhibits protein synthesis and translocation.

Kasugamycin

• Stock concentration. 10 mg/ml. Prepare using sterile distilled water . Store at 4C.
• Working concentration. Add 100 ml of stock to 1 L of media to achieve a final concentration of 1000 ug/ml (1:10).
• Mode of action. Bacteriocidal; inhibits proteins synthesis.

Nalidixic acid

• Stock concentration. 5 mg/ml. Prepare using sterile distilled water, pH 11 with NaOH . Store at 4C.
• Working concentration. Add 3.0 ml of stock to 1 L of media to achieve a final concentration of 15 ug/ml (1:667).
• Mode of action. Bacteriostatic, inhibits DNA synthesis by targeting DNA gyrase.

Rifampicin

• Stock concentration. 34 mg/ml. Prepare using sterile distilled water. Light sensitive; store stock solutions and plates in the dark at 4C.
• Working concentration. Add 4.4 ml of stock to 1 L of media to achieve a final concentration of 150 ug/ml (1:227).
• Mode of action. Bacteriostatic, inhibits RNA synthesis.

Spectinomycin

• Stock concentration. 10 mg/ml. Prepare using sterile distilled water. Store at 4C.
• Working concentration. Add 10 ml of stock to 1 L of media to achieve a final concentration of 100 ug/ml (1:100).
• Mode of action. Bacteriostatic, inhibits translocation of peptidy tRNA.

Streptomycin

• Stock concentration. 50 mg/ml. Prepare using sterile distilled water. Store at 4C.
• Working concentration. Add 0.6 ml of stock to 1 L of media to achieve a final concentration of 30 ug/ml (1:1667).
• Mode of action. Bacteriocidal, inhibits protein synthesis by binding to the S12 subunit.

Tetracycline

• Stock concentration. 12 mg/ml. Prepare in 70% ethanol and store at -20C.
• Working concentration. Add 1.0 ml of stock to 1 L of media to achieve a final concentration of 12 ug/ml (1:1000). Tetracycline is light sensitive; store solutions and plates in the dark at 4C.
• Mode of action. Bacteriostatic, inhibits protein synthesis by preventing binding of aminoacyl tRNA to the ribosome A site.

References

Data assembled from Elisabeth A. Raleigh, Karen Elbing, and Roger Brent. Current Protocols in Molecular Biology (2002) 1.4.1-1.4.14.