718 A MANUAL OF BACTERIOLOGY 



The Isolation of Specific Organisms from Water 



The principal disease-producing organisms conveyed by water 

 are the B. typhosus, B. paratyphosus, B. dysenterice, and Vibrio 

 cholerce. 



THE ISOLATION OF B. TYPHOSUS, B. PARATYPHOSUS, AND B. 



DYSENTERIC FROM WATER. Considerable difficulty is experienced 

 in isolating B. typhosus from water even when it has been copiously 

 contaminated with specifically polluted sewage ; there is, therefore, 

 far greater difficulty when the specific pollution has been small in 

 amount. The earlier records of the isolation of B. typhosus from 

 water must be accepted with scepticism, as the methods of identi- 

 fication were then incomplete and unsatisfactory. It is necessary 

 to bear in mind that usually, when drinking-water has suffered 

 sewage-pollution, the amount of the pollution is relatively very 

 minute when compared with the great bulk of the water-supply. 

 Moreover, allowing ten days as the average incubation period of 

 typhoid fever, another week before the disease comes under notice, 

 and another week before the fact that an epidemic is in progress 

 is recognised, at least a month will have elapsed between the date 

 of infection of the water-supply (supposing this to have occurred 

 on one occasion only, as may be the case) and the taking of the 

 samples for examination, a period during which all the typhoid 

 bacilli may have died out. The contamination of water may, 

 however, be of an intermittent nature ; it is rarely continuous for 

 any length of time. 



Numerous methods l have been devised for the isolation of the 

 typhoid bacillus from an infected water. With rare exceptions, 

 it is impossible to detect the organism by direct plating ; it is too 

 scanty and too mixed with other organisms to admit of this, and 

 therefore concentration of the bacterial content of the water must 

 be attempted. The following are some of the methods which have 

 been suggested for this purpose ; they serve equally well for B. 

 paratyphosus and B. dysenterice. 



1. " Filter -brushing s " method. By passing one to two litres 

 of the water through a sterile Pasteur-Chamberland filter, and 

 brushing oft the deposit into a little sterile water, the whole of 



1 See H. S. Willson, Journal of Hygiene, vol. v, 1905, p. 429 ; McWeeney, 

 Brit. Med. Journ., 1909, vol. ii, p. 866, 



