Rods which are usually motile by means of peritrichous flagella, although non-motile forms may occur. Gram-negative. Gelatin not liquefied. Indole not produced. Hydrogen sulfide production is variable. Acid is produced from glucose, mannitol, maltose and sorbi- tol. Gas production is usually observed (exceptions are Salmonella typhosa and Salmonella gallinarum, but gas production maj^ also be absent in other species or serotypes). Lactose, sucrose, salicin and adonitol are not attacked. The fermentation of other carbohydrates is variable. Acetylmethylcarbinol is not produced. Methyl red test is positive. Nitrites are produced from nitrates. Ammonium citrate is usually utilized. Urea not hydrolyzed. KCN- sensitivity is negative (Moller, VI Internat. Cong. Microbiol., Rome, ;?, 1953, 316). All known forms are pathogenic for man and/or other animals. The type species is Salmonella choleraesids (Smith) Weldin. Any organism showing the above-mentioned characters should be verified as a member of the genus Salmonella by antigenic analysis. For most practical purposes the use of poly- valent or group antisera will suflJice. Exact antigenic characterization and bacteriophage typing for epidemiological purposes is the task oi Salmonella centers. Although manj^ strains of Salmonella are at.ypical, these may be looked upon as exceptions which do not invalidate the definition of the genus. Attempts to subdivide the genus Salmonella into valid species from the taxonomic point of view have met with great difficulties. The Kauffman-White Schema (1955) (Edwards and Ewing, Identification of Enterohacteriaceae, Burgess Publishing Co., Minneapolis, 1955, 52-60) lists 343 names. It is generally agreed that the vast majority of the organisms named do not deserve species rank but should be considered as serological types. This fact has been officially recognized by the Enterohacteriaceae Subcommittee in the addendum to the report presented at the 6th International Congress for Microbiology, September 8, 1953, in Rome. "It is the recommendation of the Subcommittee that from the date of publication of this report all new serological types of Salmonella should be described by formula only and not by name." The adoption of this proposal would lead to the undesirable situation that 343 or more Salmonella types would be given names similar to those given to species, if not by meaning, certainly by implication, and that others would be known by antigenic formula only. The suggestion by Kauffmann and Edwards (Internat. Bull, of Bact. Nomen. and Taxon., 2, 1952, 5) to divide the genus into three species, namely, Salmonella cholerae- sids as type species. Salmonella typhosa on the basis of well recognized differences from other members and Salmonella enterica to serve as species for all serological types, appears too narrow and also somewhat contradictory as it practically means that two type species are chosen. Recent observations by various workers on the transduction of antigenic characters raises the question whether such changes also occur under natural conditions and should be taken into consideration in epidemiological conclusions. It is as yet uncertain whether these changes are permanent or whether reversion to the original characters occurs. Until more exact knowledge on these factors is available, the possibility must be appreciated and taken into account in epidemiological tracings. It is hardly possible to propose a classification for the salmonellas which can include all the factors established for the large number of types. However, the genus is composed of disease-producing organisms, and the first and foremost duty of any classification scheme is to make it workable under practical routine conditions. "Systems of nomenclature are for man's convenience and cannot hope to be wholly logical as to represent faithfully the evolution of all living things" (Andrewes, Acta Path, et Microb. Scand., 28, 1951, 211). From this point of view it seems justified to accord species rank to those organisms which are easily identified because they are commonly encountered and/or cause rather well es- tablished syndromes. Key to the species of genus Salmonella. I. Affect both man and other animals. A. Occur singly but not in pairs or chains.
