FAMILY IV. EXTEROBACTERIACEAE 



341 



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- 



