Key Points for Storage and Use of Penicillin-Streptomycin Solution in Animal Experiments

Why Pay Attention to Usage Details

Penicillin-streptomycin solution is a standard reagent in cell culture for many animal experiments. Its use may appear simple, but in practice, improper storage, repeated freeze-thaw cycles, or incorrect dilution ratios can all affect antibiotic activity and, in turn, affect the stability of cell culture. Understanding some basic usage points is especially helpful for those new to cell culture.

Common Specifications and Working Concentration

Commercially available penicillin-streptomycin solution is commonly supplied as a 100× concentrate, and is also available in sterile ready-to-use or lyophilized powder forms. Different laboratories can choose according to their needs. It is generally recommended to dilute the concentrate with basal medium to 1× for use, i.e., approximately 100 units of penicillin and 100 μg of streptomycin per mL of culture medium. This concentration is widely referenced in most animal cell cultures, but the specific amount used should preferentially follow the product instructions.

"Units" and "μg" are two different measurement methods. Penicillin is commonly expressed in units for activity, while streptomycin is commonly expressed by mass. Users do not need to worry about conversion; simply operate according to the dilution ratio indicated on the reagent bottle.

Aliquoting and Storage

Antibiotic solutions are relatively sensitive to the environment. After receiving a new bottle of penicillin-streptomycin, it is recommended to aliquot it under sterile conditions into small tubes, for example, each tube containing enough for one or two weeks of use. This can avoid repeated opening and freeze-thaw cycles of the entire bottle.

For long-term storage, it is generally recommended to store at around -20°C, while short-term use can be stored at 4°C.

Avoid repeated freeze-thaw cycles, because temperature fluctuations may reduce antibiotic activity.

Aliquot containers should be sterile, low-protein-binding cryogenic tubes or centrifuge tubes.

Before use, take out the required amount in advance and thaw slowly at 4°C or room temperature; do not heat at high temperature.

Observation of Color and State

Penicillin-streptomycin solution is usually a colorless to pale yellow transparent liquid. If the solution is found to be obviously turbid, darker in color, or has precipitate, use should be discontinued. These appearance changes may indicate contamination or antibiotic degradation.

During cell culture operations, after adding penicillin-streptomycin, the medium should be gently mixed. Do not add it directly onto the cell surface, so as to avoid excessively high local concentration causing irritation to the cells.

Shelf-Life Management

Even if stored properly, antibiotic reagents have a certain period of use. For solutions after opening, it is recommended to use them within the specified time. Laboratories can establish records for requisition and opening to avoid using expired reagents. Expired or improperly stored penicillin-streptomycin may not only have reduced antibacterial efficacy, but may also produce degradation products harmful to cells.

If cells in culture continuously show unexplained deterioration or increased background particles, in addition to checking aseptic technique and equipment, one can also investigate whether the penicillin-streptomycin has undergone repeated freeze-thaw cycles or has exceeded the recommended use time. After replacing with a fresh batch, observing the cell state can help determine the source of the problem.

Overall, the use of penicillin-streptomycin is not complicated, but details determine the effect. Reasonable aliquoting, standardized storage, and control of working concentration can help make cell culture in animal experiments more stable.