Sessional_Paper_1911 — Page 183

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Other Media.

For plating out and isolating Lactose fermenters from the Bile Salt tubes other media were occasionally used instead of MacConkey's Bile Salt Neutral Red Lactose Agar. The chief among these were the Conradi Drigalski Medium, Fawcus' Medium, Endo's Medium and especially Savage's modification of Endo's Medium. Of all these coloured Lactose media, perhaps Savage's modification of Endo's Medium was the most useful but none of them has in my experience any advantage in isolating Lactose fermenters over MacConkey's Medium. To be accustomed to the use of any one of these media appears to counter balance any advantage which might be derived from using another medium of which you have not had an equal experience.

METHOD OF TAKING THE SAMPLES.

Nearly all of the samples were taken by Mr. Barrington, Overseer in charge of the West Point Filter Beds, who has special knowledge of sample taking; uniformity of procedure was thus obtained.

The samples were only taken at their sources, ie., at any particular intake at the filter bed just before or just after filtration, etc.; no samples were taken from any pipe or main where the possibility of contamination might arise.

Each sample was taken into a glass stoppered bottle sterilised at 150° C., the bottle was at once put into a metal case surrounded by, but not in direct contact with ice.

The samples usually arrived at the Institute within half an hour of their collection and were examined alinost at once. There was therefore no chance of any material alteration taking place in the water between the time of its collection and the time of its examination.

Routine method of examining the samples.

With a few modifications which will be noted as they occur, the following amounts. of each sample were inoculated :-

foce

Acc

on to Agar plates.

lec

rocc

1cc

2cc

cc

1cc

2cc

Бре

16cc

1cc

2cc

Бес

10cc

MacConkey Bile Salt Neutral Red Lactose Agar plates.

MacConkey Bile Salt Neutral Red Glucose Peptone water.

MacConkey Bile Salt Neutral Red Lactose Peptone water.

20cc

50cc

These were incubated at 37° C. for 24-48 hours and were then examined, the Bile Salt peptone waters for Acid and Gas change, the Agar plates for total colonies in lcc, and the Lactose Agar plates for coli-like colonies.

Tubes showing no Acid and Gas change at the end of 48 hours were regarded as not containing B. coli.

As a rule, the three lowest Lactose tubes showing Acid and Gas change were plated on to dried Lactose Agar plates (usually MacConkey's Bile Salt Neutral Red Agar) by means of sterile glass rods.

These plates were then allowed to dry for an hour or so and then incubated at 37° C. In this way discrete colonies could practically always be obtained.