ANNUAL REPORT, 1935 21 



The Influence of Bile and Bile Salts on Aerobacter (Bacterium) 

 Aerogenes. (James E. Fuller.) A preliminary statement of this study has 

 been made previously (Mass. Agr. Exp. Sta. Bui. 315, p. 21, 1935.) The 

 medium employed was one percent each of Difco peptone, Difco lactose, and 

 K 2 HP0 4 in distilled water. Three series of cultures were set up: to one was 

 added one percent of sodium taurocholate; to another one percent of sodium 

 glycocholate; and to a third one percent of Difco ox bile. Twenty-five cultures 

 of Aerobacter aerogenes were employed. These were typical on Endo's agar; 

 they were Voges-Proskauer positive, and methyl-red, sodium-citrate, and uric- 

 acid negative. Cultures were incubated at 37°C. Once each week transfers 

 were made to fresh media of the same kind. Once each month the organisms 

 were submitted to the tests mentioned above, and stained with Gram stain. 

 The experiment was continued for five months with no change in the reactions 

 mentioned. At first there seemed to be a tendency towards some variation in 

 the Voges-Proskauer reactions but this was not persistent or uniform and was 

 probably not significant. The organisms in all three of the media produced 

 some unusual filamentous forms when they were viewed as stained specimens, 

 but this characteristic disappeared immediately when the organisms were re- 

 cultured on nutrient agar. There was greatly increased sliminess in most of 

 the cultures in the three experimental media. This characteristic also dis- 

 appeared after a few transfers of the organisms through lactose broth. The 

 experiment indicated a definite persistence of cultural characteristics for the 

 organisms examined, and consequently for the species. 



Studies on the Methyl Red Reaction. (Ralph L. France. ) The results 

 of this investigation indicated that an increase of as little as 0.04 percent 

 K 2 HP0 4 in the standard formula for the Clark and Lubs broth caused irregular 

 reactions with the Escherichia coli strains used in the experiment. A small 

 increase such as this might easily be obtained by careless weighing or by varying 

 amounts of water of crystallization in the K 2 HP0 4 . This may account for 

 the variable results obtained by different investigators using this test. On 

 the other hand, it was found possible to reduce the buffer 0.25 percent before 

 variable results were obtained with the Aerobacter aerogenes strains used in the 

 experiment. 



A Study of the Action of the Coli- Aerogenes Group on Erythrosin. 



(Ralph L. France and James E. Fuller. ) When Escherichia coli was grown in 

 a Clark and Lubs broth with 0.3 percent K 2 HP0 4 and 0.1 percent of erythrosin, 

 and with the initial pH adjusted to 7.0, sufficient acid was produced to pre- 

 cipitate the erythrosin; but when Aerobacter aerogenes was grown under the 

 same conditions, there was no precipitation of the dye. Further studies are 

 being carried on with the intermediate members of the group. 



A Study of the Eijkman Test. (Ralph L. France.) A study is being 

 made of the Eijkman broth incubated at 46°C. as a presumptive medium for 

 water analysis. At the present writing pure strains of Escherichia coli and 

 Aerobacter aerogenes and the intermediate members of the group are being 

 studied. Fecal strains of Escherichia coli will produce acid and gas in the 

 dextrose broth at 46°C. Aerobacter areogenes strains will produce acid but no 

 gas at this temperature. However, when the temperature is lowered to 45°C. 

 the aerogenes strains will produce both acid and gas. This very slight difference 

 in the temperature at which gas is produced *by coli and by aerogenes indicates 

 the need for a most accurate incubating apparatus. In this laboratory it was 

 found that a water bath was more accurate than the standard bacteriological 



