The virulence testing of the diphtheria bacillus and its practical application / by C.c. Okell and H.J. Parish.

  • Okell, C. C. (Charles Cyril), 1888-1939.
Date:
[1926?]
Catalogue details

Licence: In copyright

Credit: The virulence testing of the diphtheria bacillus and its practical application / by C.c. Okell and H.J. Parish. Source: Wellcome Collection.

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    series of cultures for injection as a control. We always employ the American strain “Park Williams 8,” since suspensions of this organism tend to produce slightly smaller reactions than most, though it is fully virulent. If this gives no reaction the whole test is repeated. An avirulent control culture may also advantageously be included. A dozen injections (i.e. two colonies from six cultures) may easily be put up on each guinea-pig. Frequently we have tested as many as 25 and occasion¬ ally 30 cultures on one guinea-pig with success, though with large numbers there is a risk of overcrowding causing fusion of the lesions, and of the guinea-pig dying of toxaemia. Without the “following dose” of 125 units of antitoxin, the intradermic injection of very few, e.g. 4 or 6 virulent cultures, may lead to the death of the guinea-pig. Unsatisfactory readings are comparatively rare. In one hundred consecu¬ tive pairs of guinea-pigs entirely satisfactory readings were obtained in 79 pairs. The control guinea-pigs showed undue reactions in four instances, the control virulent culture (Park Williams 8) gave poor reactions in 10 cases, the protected guinea-pig died in one case, and the test guinea-pig in six cases. Only in these six cases where the unprotected guinea-pig died (6 per cent, of tests) was it impossible to return a provisional report on the virulence of the cultures pending the completion of a properly controlled test. We now use two guinea-pigs unprotected except for the “following dose” of antitoxin, to ensure rapid reporting of results of the tests. Owing to the economy of the test and the ease with which it can be per¬ formed, repetition of the tests is advisable whenever there is the least uncer¬ tainty as to the readings. If two colonies of each culture are put up on two unprotected animals the tests rarely call for repetition. It would perhaps be well at this point to make clear our use of the words “virulent” and “avirulent.” We apply the word “virulent” only to those organisms morphologically resembling the diphtheria bacillus which ferment glucose but not sucrose, and which produce a toxin causing characteristic lesions in guinea-pigs. The toxic effects must of course be neutralisable with diphtheria antitoxin. In practice, we do not now consider it necessary to check the sugar reactions except in the case of cultures of special interest. (Vide Okell and Baxter, 1924.) By “avirulent” bacilli we mean organisms morphologically indistinguish¬ able from virulent bacilli, fermenters of glucose but not of sucrose, and not virulent in the above restricted sense. As a matter of fact, we have never met with an organism likely to be confused with the diphtheria bacillus, which in properly controlled tests gave consistent and characteristic intradermic re¬ actions in guinea-pigs. Reactions resembling somewhat the true reaction have been obtained with staphylococci, streptococci and in one case with B. welchii, but these cultures gave reactions both in the test animal and in the protected control.