Colicin, an ex tracellular antibiotic protein which is synthesized by some enteric bacteria, is lethal for colicin-sensi tive enteric bacteria in in vitro experiments. This observation has prompted some investigators (1)(2)(3)(4) to question whether colicin might afford a selective advantage to colicinogenic bacteria in the microbial interaction of the intestinal flora. Friedman and Halbert ( 5 ) have shown preferential intestinal establishment of antibiotic producing Escherichia coli when mixed cultures were inoculated orally into suckling mice. The role of colicin in maintaining the dominant flora has been inferred by results obtained by Branche et al.( 2 ) and Young et d. ( 4 ) . In the present study an attempt was made to further resolve this problem by utilizing an in vivo system. To afford a controlled and self-limiting gastrointestinal flora, germfree mice were inoculated, per os, with a dual colicinogenic colicin-sensitive bacterial system and the respective bacterial populations were determined. In addition, in vivo transfer of colicinogeny to the sensitive parent E . coli was studied.Materials and Methods. Bacterkl strains. Two strains, the first a colicinogenic slow lactose fermenting (SLF) "atypical Citrobacter sp.", strain CA-62, sensitive to streptomycin and producing colicin J, and the second a derivative of E. coli K-12 (Row), resistant to streptomycin and sensitive to colicin J, were obtained from Dr. nutrient broth (Difco), 8 g, were utilized with 1 and 4 gm, respectively, of NaCl added per liter. Soft agar was made with 0.7% BBL ( Baltimore Biological Laboratory) agar and 0.1% NaCl added. Eosin methylene blue agar (EMB) (Difco) was the differential plating medium. Streptomycin, at a concentration of 1000 g / m l was added to all agars when necessary.Detection of colicinogenic (Col) factor. In vitro transfer of the Col factor was detected by the agar double-layer technique of Fredericq ( 1 ) . Log phase broth cultures of colicinogenic streptomycin-sensitive CA-62 and noncolicinogenic streptomycin-resistant K-12 were mixed, incubated and plated on nutrient agar plates containing streptomycin. After 18-24hr incubation at 37", these plates were overlaid with the same colicin-sensitive K-12 incorporated in soft agar. An additional 18-24-hr period of incubation at 37" resulted in zones of inhibition surrounding the colicinogenic colonies. In the in vivo experiments, appropriate dilutions of weighed fecal samples were plated onto nutrient agar and onto EMB plates with and without streptomycin. The remaining procedure was carried out as for in vitro tests.Germfree mice. White Swiss mice, NIH strain, were obtained as germ free weanlings from the Laboratory Aids Branch, NIH. They were maintained in sterile steel Reyiers tanks or in plastic isolators and fed a semisynthetic, steam-sterilized diet, L-356 (6).Bacterial inoczdat ion. Eighteen-hour nut rient broth cultures of either CA-62 or E. coli K-12 were centrifuged and the packed viable cells resuspended to the original volume in sterile physiological ...

A new genus of the family Enterobacteriaceae is proposed on the basis of its unique biochemical and serological properties. The genus, Levinea (named in honor of Max Levine), is composed of two different species, for which the names Levinea amalonatica and Levinea malonatica are proposed. L. amalonatica is designated as the type species. The type strain of L. amalonatica is 9823 (=ATCC25405) and the type strain of L. malonatica is 179 (=ATCC 25408). Information is given which distinguishes the proposed new genus from certain species of Enterobacter and Citrobacter, the genera which it most closely resembles. The similarity of L. amalonatica t o organisms in the proposed new genus Padlewskia Macierewicz (9) is discussed. The 1966 report of the Enterobacteriaceae Subcommittee t o the International Committee on Nomenclature of Bacteria noted that the members present reaffirmed the statement that ".. . biochemically defined groups of the Enterobacterzaceae can be regarded as genera" (1). Since 1965 we recovered a number of strains of gram-negative bacteria from hospitalized patients which belong to the family Enterobacteriaceae but w h c h distinctly differ from other genera of this family by a number of biochemical properties. They are also thus far serologically unrelated t o the other genera. In the present paper the characteristics of this new genus of bacteria, which consists of two species, are described. MATERIALS AND METHODS Strains. One-hundred-andeight strains were isolated from human urine, nose, sputum, and fecal samples submitted to the laboratory for investigation. Media and Methods. The media and methods used to characterize the strains were basically those recommended in the 1958 Report of the International Subcommittee on the Taxonomy of the Enterobacteriaceae as revised by Ewing (5) and Edwards and Ewing (4). Sodium alginate medium (2) was also included.