Abstract
Standard tests for the sterility of finished vaccines or serums consist of the inoculation of 0.25 cc and. 1.0 cc from the proper number of samples of the product to Smith fermentation-tubes containing infusion-broth. The tubes are heated within 5 hours before inoculation to drive off dissolved oxygen. They are then inoculated and are incubated for 7 days. The presence of weak points in the standard procedure has long been suspected.
The inherent weaknesses of the standard test are, in part, dependent upon (1) the frequent use of merthiolate which, because of its bacteriostatic effect, prevents the growth of contaminants, if any, in many instances; and (2) standard Smith tubes are not well adapted to the cultivation of anaerobes. The use of a second transfer, after 7 days, from optically clear Smith tubes to fresh Smith tubes in an endeavor to overcome the bacteriostatic action of the preservative is definitely irrational and thus unsatisfactory. 1
The use of Brewer's medium 2 containing thioglycollate overcomes the objections given because it permits the growth of organisms in the presence of merthiolate and because it is suited to the cultivation of anaerobes. The results reported here support these views.
Tests were made with vaccines (bacterins) and serums, preserved with merthiolate, 1:5000 or 1:10,000, or with phenol, 0.5%. As contaminants 24-hour cultures of Staph. aureus, Staph. albus, Ps. pyocyanea, B. subtilis and C. xerosis were used. 3 In addition, there were available dried spores of Cl. tetani in sand, 10 years old, prepared by Coleman. 4 Vaccines and serums were inoculated lightly with these organisms, singly and in mixtures. From these products 0.25 cc and 1.0 cc respectively, containing from 5 to 500 organisms, were transferred to standard Smith tubes and also to tubes containing 12 cc of thioglycollate medium.∗ Incubation at 37 °C for 7 days followed, with frequent observations.
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