Cefotaxime Stock Solution 250 mg/mL: Preparation Protocol

Cefotaxime Stock Solution (250 mg/mL) is a ready-to-use, sterile-filtered antibiotic reagent designed to facilitate precise dosing in plant tissue culture, Agrobacterium elimination, and gram-negative bacterial selection workflows.

Concentration

250 mg/mL

Antibiotic Class

Third-generation cephalosporin (beta-lactam)

Primary Applications

Plant tissue culture, Agrobacterium tumefaciens elimination, gram-negative bacterial selection

Recommended Storage

−20 °C, protected from light; avoid repeated freeze-thaw cycles

Sterilization

Sterile-filtered (0.22 µm membrane)

Typical Working Concentration

100–500 µg/mL (dilute 1:500 to 1:2500 from stock)

Overview and Mechanism of Action

Cefotaxime is a third-generation, broad-spectrum beta-lactam antibiotic that inhibits bacterial cell wall biosynthesis by acylating penicillin-binding proteins (PBPs), ultimately leading to cell lysis. It demonstrates potent activity against a wide range of gram-negative organisms, including Agrobacterium tumefaciens, making it indispensable in plant genetic transformation workflows where contaminating bacteria must be eliminated after co-cultivation.

The pre-formulated 250 mg/mL stock solution supplied by Aladdin Scientific eliminates the need for weighing and dissolving antibiotic powder, thereby reducing preparation time, minimizing variability between experiments, and lowering the risk of contamination. The solution is sterile-filtered through a 0.22 µm membrane and is ready for direct dilution into culture media or buffers.

Materials and Equipment

• Cefotaxime Stock Solution 250 mg/mL (Aladdin Scientific, SKU: C1529773)
• Sterile deionized water or appropriate culture medium (e.g., MS medium, LB broth)
• Calibrated micropipettes and sterile tips
• Sterile 1.5 mL or 15 mL tubes
• Laminar flow hood or biosafety cabinet
• Vortex mixer
• −20 °C freezer for storage

Note: All dilution steps should be performed under aseptic conditions to maintain sterility of the working solution.

Step-by-Step Protocol

1. Thawing and Inspection

Remove the Cefotaxime Stock Solution (250 mg/mL) from −20 °C storage and allow it to thaw at room temperature (15–25 °C). Inspect the solution for particulates or discoloration. Discard the vial if the solution appears turbid or has changed color, as this may indicate degradation.

2. Preparing the Working Solution

Determine the required final concentration for your application. Common working concentrations are listed below:

• Plant tissue culture (Agrobacterium elimination): 250–500 µg/mL — dilute stock 1:500 to 1:1000 in sterile medium.
• Gram-negative bacterial selection: 100–200 µg/mL — dilute stock 1:1250 to 1:2500 in sterile medium or buffer.

Example: To prepare 100 mL of medium containing 500 µg/mL cefotaxime, add 200 µL of the 250 mg/mL stock to 99.8 mL of sterile medium. Mix gently by inversion or vortex. Do NOT autoclave the medium after addition, as heat will degrade the antibiotic.

3. Addition to Culture Medium

Allow autoclaved agar medium to cool to 50–55 °C before adding the cefotaxime working aliquot. Mix thoroughly but gently to avoid bubble formation, then pour plates or dispense into culture vessels immediately.

4. Aliquoting and Storage of Unused Stock

If the entire stock volume is not required immediately, aliquot the remaining solution into sterile, light-protected microtubes (e.g., amber or foil-wrapped). Store aliquots at −20 °C. Use each aliquot only once to avoid repeated freeze-thaw cycles that can degrade antibiotic potency.

Troubleshooting and Critical Notes

Problem	Possible Cause	Recommended Action
Persistent bacterial contamination	Working concentration too low; antibiotic degraded	Increase cefotaxime concentration; use fresh stock aliquot; verify storage conditions
Phytotoxicity observed in plant cultures	Working concentration too high for sensitive species	Reduce concentration; consult species-specific literature for optimal range
Antibiotic precipitation in medium	Medium temperature too low when antibiotic added, or incompatible medium components	Ensure medium is at 50–55 °C at time of addition; check medium composition for incompatible salts
Color change of stock solution	Degradation due to improper storage or light exposure	Discard lot; store replacement at −20 °C in light-protected conditions

Important: Cefotaxime should not be used as the sole selection agent in mammalian cell culture applications without verifying cytotoxicity profiles for the specific cell line in use.

Frequently asked questions

What is the recommended working concentration of cefotaxime for eliminating Agrobacterium tumefaciens in plant tissue culture?

The commonly used working concentration range for Agrobacterium elimination is 250–500 µg/mL, though the optimal concentration may vary depending on the plant species and transformation protocol. Always consult species-specific literature or pilot experiments to confirm the appropriate dose.

Can the cefotaxime stock solution be added to autoclaved medium before it solidifies?

Yes, but only after the autoclaved medium has cooled to 50–55 °C. Adding cefotaxime to medium that is too hot will cause thermal degradation of the antibiotic and reduce its efficacy. Never autoclave medium after adding the antibiotic.

How should unused Cefotaxime Stock Solution (250 mg/mL) be stored to maintain potency?

Unused stock should be aliquoted into sterile, light-protected tubes and stored at −20 °C. Avoid repeated freeze-thaw cycles, as these can degrade the antibiotic. Each aliquot should be used only once after thawing.

Is cefotaxime effective against gram-positive bacteria?

Cefotaxime has some activity against certain gram-positive organisms, but its primary strength lies in broad-spectrum gram-negative coverage. For applications requiring gram-positive bacterial selection or elimination, additional or alternative antibiotics should be considered.

Why does the cefotaxime solution appear slightly yellow, and is this normal?

A slight yellow tint is characteristic of cefotaxime solutions and is considered normal. However, if the solution becomes deeply discolored, turbid, or develops particulates, this may indicate degradation, and the lot should be discarded.

References

1. Hoekema A, et al. Use of cefotaxime to eliminate Agrobacterium tumefaciens from transformed plant tissues. Plant Molecular Biology Reporter. (General reference — specific volume/page needs verification.)
2. Murashige T, Skoog F. A revised medium for rapid growth and bio assays with tobacco tissue cultures. Physiologia Plantarum. 1962;15(3):473–497. doi:10.1111/j.1399-3054.1962.tb08052.x
3. Schenk RU, Hildebrandt AC. Medium and techniques for induction and growth of monocotyledonous and dicotyledonous plant cell cultures. Canadian Journal of Botany. 1972;50(1):199–204. (Cited as general antibiotic use context in plant culture — verify relevance.)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.