Impure and misnamed stock cultures of obligate anaërobes

Abstract

During the past few years the writer has engaged in building up a collection of cultures of obligate anaërobes whose purity and true identity should be, if possible, beyond question. In addition to numerous cultures isolated from original sources a number have been received from other laboratories. Most of these were already labelled as to species and form the subject of this report.

While a few cultures were received with aërobic contamination these are not included here since aërobic contaminations are 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 aërobes, 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.

This experience indicates that the majority of anaërobic cultures received from other laboratories are pure but that a surprisingly large number contain or consist of resistant species not indicated by their labels. B. sporogenes is the commonest organism found in stock cultures of anaërobes.

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 anaërobic contamination is imperfectly sterilized culture medium.