“Symbiotic Fermentation Phenomenon,” Its Use in Differentiation of Microorganisms and Identification of Carbon Compounds.

Abstract

The phenomenon called symbiotic fermentation may be defined as follows: “Two microorganisms neither of which alone produces fermentation with gas in certain carbohydrates may do so when living in symbiosis or when artificially mixed.” I noted the phenomenon in 1904 and 1905 1 ; I observed that ordinary baker's yeast in Ceylon and England, as a rule, consisted of two or more organisms (saccharomyces and bacilli) living in symbiosis, and that baker's yeast in toto gas-fermented a larger number of sugars than any of the isolated organisms. In recent years I have used principally pathogenic bacilli. The phenomenon takes place using only certain organisms, one of which apparently must be capable of producing acidity (never gas) in certain carbohydrates.

Examples: I. B. typhosus alone does not produce gas in maltose (acidity only); B. morgani alone does not produce gas in that sugar (neither acidity nor gas). The mixture B. typhosus + B. morgani will produce gas.

II. Staphylococcus aureus (Ross Institute strain) alone does not produce gas in maltose (acidity only); B. morgani alone does not produce gas (neither acidity nor gas); the mixture Staphylococcus aureus + B. morgani will produce gas.

Liquid media. The phenomenon is easily put in evidence by using the test tubes containing a Durham's fermentation tube or saccharomyters. It is essential that the liquid media (maltose, mannitol, etc.) should be made with sugar-free peptone water, not broth, which as well known usually contains a small amount of glucose.

Solid media. The phenomenon is very evident when solid media are used. The solid sugar media (maltose-agar, mannitol-agar, etc.) are prepared in the usual way, but in the preparation of the agar, sugar-free peptone water must be used, not broth, because broth as a rule contains a little glucose.