significant quantities of ethanol and acetic, lactic and succinic acids with only traces of formic acid. Acetylmethylcarbinol and 2,3-butylene glycol have not been found (Voges-Proskauer test negative). Salts of citric acid are utilized as sole sources of carbon. Nitrites produced from nitrates. Catalase-positive. Aerobic, facultatively anaerobic. Temperature requirements: Growth at 10° and at 45° to 46° C. Optimum growth tem- perature, between 30° and 37° C. Gas not produced in Eijkman tests, although some cultures show growth at 45° to 46° C. Salt tolerance: Most cultures ferment glucose in the presence of sodium chloride in a concentration of 6.0 to 7.0 per cent. A few cultures tolerate 8.0 per cent sodium chloride. Optimum pH, about 7.0. Growth occurs between pH 5.0 and pH 8.0. Serology: As noted under Escherichia freundii, the serology of the citrate-positive species placed in Escherichia has not been studied extensively. So far as known, no studies have been made to determine whether there are detectable serological differences between the citrate-positive cultures that produce hydrogen sulfide in proteose peptone, ferric citrate agar (E. freundii as defined by Vaughn and Levine, Jour. Bact., U, 1942, 502) and the citrate- positive cultures that do not produce hydrogen sulfide on the same medium {E. intermedia as defined by Vaughn and Levine, loc. cit.). Comments: Vaughn and Levine {loc. cit.) have given reasons for combining two of the seven species of Citrobacter described by Werkman and Gillen (Jour. Bact., 23, 1932, 177) that do not produce hydrogen sulfide into a single species for which they use the name Escherichia intermedia. It should be noted that the description as given above is based on their definition. The specific epithet intermedia is used here in a more restricted sense than is the general term "intermediates," which is frequently applied to all citrate-positive species of coliform organisms. Habitat: Normally found, to a varying degree, in soil, water and in the intestinal canals of man and other animals. Widely distributed in nature. Genus II. Aerobacter Beijerinck, 1900.* (Cent. f. Bakt., II Abt., 6, 1900, 193.) A.e.ro.bac'ter. Gr. mas.n. aer air, gas; M.L. noun bacter the masculine equivalent of Gr. neut. n. bactrum a small rod; M.L. mas.n. Aerobacter a gas (-producing) rod. Short rods. Motile or non-motile, the motile species possessing peritrichous flagella. Gram-negative. Grow readily on ordinary media. Ferment glucose and lactose with the pro- duction of acid and gas. Produce two or more times as much carbon dio.xide as hydrogen from glucose. Methyl red test negative; Voges-Proskauer test positive. Trimethyleneglycol not produced from glycerol by anaerobic fermentation. Citric acid and salts of citric acid are utilized as sole sources of carbon. Aerobic, facultatively anaerobic. Widely distributed in nature. The type species is Aerobacter aerogenes (Kruse) Beijerinck. Key to the species of genus Aerobacter. I. tGlycerol fermented with the production of acid and gas. Gelatin not liquefied (rarely liquefied). 1. Aerobacter aerogenes.
- Prepared by Prof. M. W. Yale, New York State Experiment Station, Geneva, New
York, July, 1943; revised by Prof. Robert S. Breed, Cornell University, Geneva, New York, in consultation withinvestigatorswhohave made special studies of this genus, October, 1955. t Kligler (Jour. Inf. Dis., 16, 1914, 187) found the fermentation of glycerol to be inversely correlated with gelatin liquefaction and considered the former the more reliable as a charac-
