In the bacteriological laboratories of Brown University and the Connecticut State Department of Health, Bureau of Laboratories, we have been engaged in a systematic study of the biochemical and serological relationships of the coliform and related bacteria since April 1937. During this time over 12,000 normal and aberrant coliform cultures have been isolated. The IMViC reactions and in addition cellobiose fermentation were determined for all these cultures. A wide variety of biochemical types were encountered ranging from those positive in all five tests to a few weakly positive in only one of the IMViC tests. The ability of more than 3,500 of these cultures to ferment glucose, lactose, sucrose, salicin, maltose and mannitol was determined. Normal coliform cultures negative in sucrose or salicin or both were commonly found. Strains failing to ferment maltose were not anticipated but several were isolated from widely different sources. Mannitol fermentation appeared to be a constant characteristic of normal coliforms but among the last 500 isolations two, otherwise normal, mannitol-negative strains were obtained.Coliform cultures fermenting lactose slowly or not at all, but normal in other respects, were frequently encountered. We have obtained from both rapid and slow lactose-fermenting coliforms variants which were anaerogenic in lactose only or in all carbohydrates. Some of these variants have remained constant for 2 years, one for more than 3 years. In addition motile and nonmotile, indolepositive cultures were found which produced no gas from carbohydrates when originally isolated. Many such cultures would be classed as Eberthella or Shigella, particularly when the fermentation of lactose, sucrose or salicin was slow or absent. After varying periods of laboratory cultivation many of these strains produced gas. Cultures that appeared to be non-gas-forming but which could not be identified as known Eberthella or Shigella have been included in the paracolon group since they could be anaerogenic variants of coliforms.These exceptions and others are a serious handicap to the practical bacteriologist because strains not infrequently defy classification in any of the recognized sections of the coliform group. The tendency to disregard such exceptions for the most part is justifiable but occasionally this might be a mistake. Stuart, Mickle and Borman (1940) proposed the term "aberrant" coliforms for cultures not fermenting lactose, producing acid only, or requiring more than 48 hours for the production of 20 per cent gas when the unusual fermenting characteristics of such strains are relatively stable. Aberrant coliforms are frequently isolated from such sources as water with an excellent sanitary survey, soils from rigidly 101 on August 5, 2020 by guest http://jb.asm.org/ Downloaded from 140 paracolon Aerobacter cultures were actively motile.Paracolon Aerobacter can be separated into 2 divisions on the basis of their IMViC reactions. Division 1 consists of 48 strains which gave a strong Voges-Proskauer reaction, gr...
Most approaches to the problem of bacterial taxonomy have arisen from either of two viewpoints, one derived from phylogenetic and the other from practical considerations. The former viewpoint too frequently arises from some major premise which has little practical connotation. The latter viewpoint often leads to the submergence of large groups of bacteria, not known to be of economic importance, because of an attitude of impatience toward any system which does not reflect the methods used in the specialized laboratory where steps in the identification of an unknown organism must be measured in terms of utility and speed. Regardless of personal viewpoints, it must be realized that precise delineation of species cannot be the primary aim of bacterial taxonomy at present. It is seldom possible and often it may not even be desirable. We must compromise by recognizing the necessity for the organization within a taxonomic system of a selected body of knowledge of important differential characters which may be applied when practical considerations demand that phylogenetically related organisms be distinguished, one from another. In addition, the taxonomic system should suggest, by implication if not by statement, the fields and directions in which further investigation is necessary or may prove fruitful. This implies that taxonomic systems must undergo periodic revision with the advent of new knowledge. This discussion will be concerned with the taxonomic system followed for the Enterobacteriaceae in the fifth edition of "Bergey's Manual of Determinative Bacteriology" (Bergey, Breed, Murray and Hitchens, 1939). THE FAMILY Enterobacteriaceae Rahn (Zentr. Bakt. Parasitenk., II, 96, 280, 1937) The difficulties besetting the taxonomist in devising and revising a classification are well illustrated by the family Erterobacteriaceae. New knowledge of this group has accumulated to such an extent that incorporation of it into our present system produces a confusingly top-heavy struc'ture. Furthermore, satisfactory labeling of many forms with intermediate characteristics is not now possible even though those forms are commonly encountered in practical work. Not only is simplication needed but also reconstruction of the general framework of-the system so that it will provide more effectively than it now does for the absorption of newly described types. This family, while not discontinuous with other bacterial families, is so well delineated by tradition and usage that no radical change in its definition is 351
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