Stock Cultures of Obligate Anaerobes. 



3i5 



readily recognized and eliminated by the bacteriostatic action of 

 selective dyes 1 or by selective heating according to whether the 

 contaminants form spores or not. 



No assumptions as to purity or correct identity were made; 

 after ascertaining the absence of aerobes, every culture was first 

 carefully examined for the salient properties of the indicated 

 species in order to determine, (1), its presence or absence, and (2), 

 the possible presence of contaminating organisms. Irrespective 

 of the findings in the preliminary tests, every culture was regarded 

 as possibly impure and was therefore purified and repurified from 

 three to six times by either the deep colony, or the surface colony 

 method or both. 2 The pure culture was then identified. 



Following are the results briefly tabulated. 



More than one species of anaerobe (6 cultures) 



Containing the designated species 5 cultures 



Not containing the designated species I 



No evidence of anaerobic impurity (40 cultures) 



Renamed in accord with recently accepted nomenclature 7 cultures 



Incorrectly labelled 13 14 



Correctly labelled 20 " 



Total 46 cultures 



This experience indicates that the majority of anaerobic cul- 

 tures received from other laboratories are pure but that a sur- 

 prisingly large number contain or consist of resistant species not 

 indicated by their labels. B. sporogenes is the commonest or- 

 ganism found in stock cultures of anaerobes. 



The writer believes that many of the cultures were pure and 

 properly identified in the beginning of their history which in some 

 cases goes back many years and involves transfers between several 

 laboratories. The most probable source of anaerobic contamina- 

 tion is imperfectly sterilized culture medium. Once contaminated 

 a culture may readily lose the possibly less resistant species in- 

 dicated by its label while the contaminant may persist indefinitely 

 without detection by any but one skilled in anaerobic bacteriology-. 



A few instances have been observed in our own laboratory in 

 which pure cultures of anaerobes became contaminated and the 



1 Hall, "Selective elimination of hay bacillus from cultures of obligative ana- 

 erobes," Jour. A. M. A., 1919, lxxii, 274. 



2 Hall, "Practical methods in the purification of obligate anaerobes," Jour. 

 Infec. Dis., 1920, xxvii, 576. 



