Streptomycin, assay standards

Extractions traditionally have been performed using buffers (j ) the same used to obtain the maximum response in standard curves. Unfortunately this has been a major failing of the plate diffusion assay systems. It is rare that the pH can be adjusted to the optimum necessary for greatest response simply by blending a matrix with buffer. As much as a 30 to 40% loss of activity can occur by not adjusting the pH properly analysis for residues of the streptomycins and erythromycin, for example, can yield results 20% lower by having the pH of the analyte 0.2 units below 8.0 if the pH is 0.5 units below 8.0, the loss of potency approaches 50% (14-15). 

The cytotoxicity assay is usually performed by determining the viability of suitable cell lines in the presence of polymers. For this test, 3-5 mm discs of polymer film are cut and sterilised under standard conditions (at 121 C and 6.8 kg (15 lb) pressure for 15 min). The cell growth in the presence of the polymer films is measured under a controlled atmosphere (CO2 incubator, 37"C) using an appropriate culture medium, supplemented by 10% fetal bovine serum and penicillin-streptomycin antibiotic solution. Confluent monolayers are propagated by trypsinisation (0.25% trypsin and 0.02% EDTA, ethylene diamine tetraacetic acid) and re-plated at 2 x 10 cells/mL in a sterile polystyrene cell culture plate, then incubated for 24,48 and 72 h. The morphology of the cells is analysed by light naicroscopy (Leica) after... 

There are two generally accepted methods for the assay of streptomycin and dihydrostreptomycin. The plate diffusion assay uses a spore suspension inoculum and a technique almost identical to the penicillin plate assay described above. It has been the authors experience that the turbidimetric assay described below is more precise. This method is also applicable to dihydrostreptomycin with appropriate substitution of the standard. 

Assay Technique. Sample dilutions and standard dilutions may be prepared exactly as for penicillin (Section IV,1). By the addition of 0.6 ml. of standard streptomycin solution to the first two tubes in the series followed by dilution through tube 12, concentrations are obtained which range from 10.0 pg. in tube 1 to 0.0045 pg, in 12. 

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