The presence of iron depositing bacteria in milk.

Abstract

Harder 1 has made a careful study of the group of microorganisms, generally classed by him as the trichobacteria, to which he ascribes the deposition of certain sedimentary iron ores. Although Harder 'devotes himself largely to these trichobacteria, he mentions finding a number of bacteria (eubacteria) which were also able to precipitate ferric hydroxide and other ferric salts from media containing iron salts of organic acids. Since these iron depositing bacteria are soil types, it is not surprising that to a greater or lesser degree they should be found in milk and its products.

The ferric ammonium citrate media of Harder was used both as a broth and as a solid medium. On the agar were obtained colonies described by Harder as typical; that is, large, irregular, iron-incrusted colonies. Other types as well were found. Of the organisms forming these colonies, cocci and bacilli seem to occur in about equal numbers. There were very few spore formers, no motility, and no liquefaction of gelatin. Dextrose is fermented but lactose and saccharose only rarely so. As a class these organisms were able to utilize the salts of organic acids for their source of carbon, the pH of the medium rising distinctly. Thus they correspond to the group of alkali bacteria studied by Ayers. 2

The knowledge of the presence of these organisms in milk is believed to be new and significance is attached to them, since frequently undesirable qualities are found in the milk when they are present in considerable numbers.