48 ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 
EXERCISE 71 
CONFIRMATORY TESTS FOR BACTERIUM COLI IN WATER 
Isolate cultures from acid producing colonies found in some of the samples 
of water which have given presumptive tests for organisms of the coli-aerogenes 
group. 
Make further studies to confirm these cultures as belonging to the coli-aero- 
genes group. Determine also whether they belong to the coli or aerogenes divi- 
sion of the group, and their probable species. 
Determine: (1) morphology, (2) staining reactions, (3) spore formation, 
(4) cultural characteristics on agar slopes, (5) -gelatin liquefaction, (6) indol 
production, (7) milk reactions, (8) methyl red test, (9) Voges-Proskauer reac- 
tion, (10) fermentation reactions in glucose, lactose, and sucrose broths. 
EXERCISE 72 
LACTOSE PEPTONE BILE MEDIUM 
Inoculate Smith fermentation tubes containing lactose peptone bile with 
cultures of Bacterium coli and Bacterium aerogenes and with 1/10 cc. of a 
sample of polluted water. Incubate at 37° C. 
The composition of the lactose peptone bile used for this purpose is: 
Lactose 1.0% 
Peptone 1.0% 
Oxgall (dried) 5.0% 
Five per cent of dried oxgall gives a solution of about one-half the strength 
of the bile as it comes from the gall bladder. 
The principle underlying the use of bile in the examination of water is that 
it inhibits the growth of many bacteria not of intestinal origin, while inhibiting 
only slightly or not at all the intestinal types. 
EXERCISE 73 
ENDO MEDIUM 
By the loop dilution method, plate out cultures of Bacterium coli and Bac- 
terium aerogenes on Endo’s agar. Incubate at 37° C. 
The composition of Endo medium is: 
Dibasic potassium phosphate 0.35% 
Peptone 1.0% 
Agar (washed) 1.5% 
Lactose 1.0% 
