Mechanism of action of penicillin-streptomycin and quality observation of animal experimental reagents

Mechanisms of action of two antibiotics

Penicillin belongs to the β-lactam class of antibiotics. Its primary target is the peptidoglycan synthesis process in the bacterial cell wall. Animal cells do not have cell walls, so from a mechanistic standpoint, the direct effect of penicillin on animal cells is relatively limited. Streptomycin belongs to the aminoglycoside class of antibiotics. It can bind to bacterial ribosomes, interfering with bacterial protein synthesis and preventing bacteria from growing and reproducing normally.

In plain terms, penicillin is like destroying the "outer wall" of bacteria, while streptomycin is like disrupting the "factory" of bacteria. When used in combination, they can inhibit bacteria at different stages, which is one of the reasons they are paired together in cell culture.

Why conventional concentrations are relatively safe

There are structural differences between animal cell ribosomes and bacterial ribosomes, and streptomycin has a higher affinity for bacterial ribosomes at conventional working concentrations. However, any antibiotic carries some risk of cytotoxicity, especially at excessively high concentrations or with prolonged exposure. At higher concentrations, streptomycin may affect mitochondrial function or protein synthesis in certain mammalian cells. Therefore, it is not recommended to arbitrarily increase the concentration of the penicillin-streptomycin dual antibiotic solution.

In general cell culture, when penicillin-streptomycin is used together, the common working concentrations are 100 units/mL penicillin and 100 μg/mL streptomycin. This range has been accepted by many laboratories through long-term use, but for primary cells, stem cells, or sensitive cells specifically, professional literature and preliminary experiments should be consulted.

Quality considerations for bioreagents

Cell culture antibiotics used for animal experiments, unlike clinical drugs, are typically managed as bioreagents or research-grade reagents. When purchasing, it is advisable to pay attention to the following points:

Whether it is cell culture grade: such products generally have controlled specifications for endotoxin, sterility, and other indicators.

Whether a certificate of analysis is available: reputable suppliers provide basic information such as lot number, sterility testing, and potency.

Packaging and storage instructions: clearly labeled storage temperature, shelf life, and dilution ratio.

Appearance and solubility: after opening, observe whether the liquid is clear and free of abnormal particles.

It should be noted that differences in manufacturing processes and quality standards may exist among different suppliers. Even if the main components are the same, factors such as excipients, purity, and endotoxin levels may also affect cell culture outcomes. When changing brands or lots, laboratories should preferably conduct small-scale trial use to observe whether cell status remains stable.

Reasonable expectations and usage recommendations

Penicillin-streptomycin is a common preventive additive in basic culture media, not a therapeutic drug. It can help reduce the risk of certain bacterial contamination, but it cannot solve all contamination problems. In animal experiments, the stability of cell culture quality also involves multiple factors including culture media, serum, and culture consumables.

If an experiment has high requirements for cell status, such as primary isolation, single-cell cloning, or long-term induced differentiation, one may first test whether a culture system without dual antibiotics is feasible, or choose a lower-concentration maintenance protocol. Any adjustment should be based on preliminary experiments and documentation, avoiding blind changes to conditions.

Understanding the principles and limitations of penicillin-streptomycin helps researchers make more rational choices in selecting and using these reagents, reducing waste and lowering the probability of results being confounded by contamination.