A Brief Survey of the Group of Acid-Producing and Acid-Tolerating Bacteria Known as the Lactobacillus Genus *

The Lactobacillus genus, which is without question one of the most widely distributed groups of microorganisms in nature, and to which important economic roles have been attributed, possesses the following generic properties. The individual cells are rod-shaped, their length and thickness varying in a large measure with the nutrient medium in which they are grown, and according to the species. In young cultures they are Gram-positive, a property which is often lost, at least in part, as the cultures grow older. They are non-motile and non-sporulating. They produce delicate growths, as a rule, on artificial media, and in many instances do not submit readily to artificial cultivation. They vary in their oxygen requirements from facultatively anaerobic to micro-aerophilic. The above description alone does not serve to distinguish the lactobacilli from other known forms, as, for example, the genus Kurthia (zopfii and zenkeri). The members of the Lactobacillus group are primarily fermentative, and possess at best but little proteolytic property. They act upon various carbohydrates, and produce lactic acid, often in considerable quantities. One of the properties which has attracted particular attention is their peculiar tolerance for free organic acids; hence the term "aciduric" as applied to the members of this group. The different species vary considerably in their ability to attack carbohydrates, and in the amounts and kinds of acid produced. For example, while many decompose lactose, others do not. Again, some readily attack the pentoses, xylose and arabinose, while others are without this property. Then, whereas a large number form lactic acid, with only very small amounts of by-products, others produce, in addition to lactic acid, appreciable amounts of other substances, particularly acetic acid and alcohol. The first known organism of the aciduric group was described by Kern, in 1 88 1, as Dispora caucasica, and later studied and renamed by Beijerinck Lactobacillus caucasicus. It was isolated from kefir. It dosely resembles the L. bulgaricus of Grigoroff, the first account