174 MEDICAL BACTERIOLOGY 



When a sample has been obtained it should be examined as soon as possible. 

 If time must elapse before examination, the sample should be cooled to i5C. 

 and maintained at or below that temperature until examined. 



Samples for bacteriological examination are collected in sterile receptacles, 

 measured with sterile pipettes and cultured in sterilized tubes and dishes. 



TECHNIQUE 



Fermentation Test. Shake container to evenly distribute bacteria that 

 may be in the water. Take a number of fermentation tubes containing lactose 

 broth medium. 



Put o.i cc. into each of the first two tubes. 



Put 0.2 cc. into each of the second two tubes. 



Put 0.4 cc. into each of the third two tubes. 



Put 0.8 cc. into each of the fourth two tubes. 



Put 1.5 cc. into each of the fifth two tubes. 



Put 3 .o cc. into each of the sixth two tubes. 



Put 6.0 cc. into each of the seventh two tubes. 



Put 10. o cc. into each of the eighth two tubes 



Place one set of tubes containing the various amounts of water in an incu- 

 bator at 37C. and the others in an incubator at room temperature. 



Examine these tubes at 24-hour intervals for 3 days. 



If fermentation occurs gas accumulates at the top of the tube. When fer- 

 mentation occurs it is due to the presence of the colon bacillus in the majority 

 of cases, but one must remember that other organisms can, and occasionally do, 

 cause fermentation even when the water is free of colon bacilli, usually bacillus 

 Welchii. 



Plating. A number of tubes of litmus lactose agar are liquefied by placing 

 in a water bath and hearing to the boiling point. They are then cooled to 45C. 



Put o.i cc. of water into the first tube and empty tube into Petri dish. 

 Put o. 2 cc. of water into the second tube and empty tube into Petri dish. 

 Put 0.4 cc. of water into the third tube and empty tube into Petri dish. 

 Put o . 8 cc. of water into the fourth tube and empty tube into Petri dish. 

 Put 1.5 cc. of water into the fifth tube and empty tube into Petri dish. 

 Put 2.0 cc. of water into the sixth tube and empty tube into Petri dish. 



Make a duplicate set of plates, using 2 or 3 per cent, plain agar having a 

 reaction of +1.5. Incubate one set at room temperature, the other at 37C. 



Count the colonies every 24 hours for 3 days. 



When water is dropped into a tube of agar the tube should be inverted several 

 times to evenly distribute the water before pouring into a Petri dish. Care 

 should be taken to distribute the liquid agar evenly over the entire bottom of the 

 Petri dish and the dish should not thereafter be tilted, moved nor placed in 

 incubator until the agar has solidified. 



The colon bacillus and other organisms that ferment lactose turn litmus lac- 

 tose agar red. When red colonies appear they are removed from the plates 

 with a sterile platinum loop and planted in Dunham's solution, litmus milk, 



