Practical bacteriology for chemical students / by David Ellis.

  • David Ellis
Date:
1923
Catalogue details

Licence: In copyright

Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.

    105/152 (page 93)
    Exercise 75. The Search for Bac. enteritidis sporogenes. This organism is supposed to cause outbreaks of epidemic diarrhoea. It is present (about 100 per c.c.) in crude sewage and entirely absent from pure water and virgin soil. If water is very much contaminated, showing obvious sewage pollution, an attempt should be made to ascertain if E. enteritidis sporagenes is present. This organism has two great advantages for purposes of isolation. 1. It forms spores. 2. It grows best under anaerobic conditions. Hence if we heat the sample up to about 800 C. all organisms will be killed except those in the spore-condition. This limits the numbers considerably. Further, if the culture be made under anaerobic conditions only spore-forming anaerobes will develop. 1. Place about 5 c.c. of sample-water in a sterile tube and insert in a pan containing water at about 80 0 C. Keep tube in water at this temperature for about 15 minutes. 2. Melt contents of Nutrient-agar tube. 3. Pour the heated sample-water into Agar-tube. 4. After mixing contents pour into a sterile Petri-dish, following directions given in Exercise 45. 5. Incubate at 37 0 C. All the colonies that appear within 5—7 days may be regarded as Bac. enteritidis sporogenes. * Exercise 76. To find the number of gelatine-liquefying bacteria in 1 c.c. of sample. If the contamination is known to be very large this exer- cise may be set on foot to give a measure of confirmation to the other exercises. The value of the test consists in this, that it is known that not only does crude sewage contain many liquefying bacteria, but it is known that many of these are of an undesirable kind. * It is possible that the colonies may be Bac. butyricus or Bac. cadaveris but not probable if pollution is known to be due to sewage.