Laboratory Outline for General Bacteriology 



grown for the required length of time tests are made as follows: 

 With sterile pipette remove 2 cc. of culture to a clean test tube. Add 

 1 cc. of test solution which is made up of naphthylamin, acetic acid, 

 sulphanilic acid and water. A pink color shows the presence of 

 nitrite. Test an uninoculated tube in the same manner for a con- 

 trol. Observations are made for gas bubbles rising in the nitrate 

 broth cultures. 



NITRATE AGAR 



Nitrate agar is the same as standard agar with .1 per cent 

 KNO . added. It is used in slants, which are inoculated by making 

 both a streak on the surface and a stab to the bottom of tube. The 

 test solution is poured over the surface of the medium. Gas pro- 

 duction is shown by cracks in the agar. 



HYDROGEN SULPHIDE 



A beef extract agar very rich in peptone and containing lead 

 acetate is used in tubes. This is inoculated by stabbing with a 

 straight needle. A darkening of the medium within a few days 

 shows that hydrogen sulfide has been produced. 



INDOL PRODUCTION 



Cultures are grown in Dunham's peptone solution. It is com- 

 posed of peptone, sodium chloride and distilled water. After four 

 days the Ehrlich test is made as follows: Add to the culture 1 cc. 

 of a 2' '< solution of paradimethylaminobenzaldehyde in 95 ' < alcohol. 

 Then add drop by drop y cc. of concentrated HC1. If indol is pres- 

 ent a pink zone appears which deepens and widens on standing. 

 The test may be confirmed by shaking the culture with chloroform 

 to see if the pigment dissolves. If it proves soluble the test is 

 considered positive. 



FERMENTATION TUBES 



The medium is nutrient broth with one per cent of the different 

 sugars added. It is put into tubes in which are small inverted 

 inner tubes which are also filled with the medium. If gas is formed 

 some of it will collect in the inner tube and the percentage can 

 be measured by the gasometer chart shown on page 41. If the 

 bacteria grow only within the inner tube (this is shown by cloudi- 

 ness or sediment) it shows that they can grow only in the absence 

 of oxygen and are anaerobic. When growth occurs only outside 

 the small tube it shows that the bacteria require oxygen and are 

 aerobic. When growth occurs both inside and outside the inner 



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