BACTERIA IN ILKM 1047 



bacillus was used cither in milk culture or in broth in which it was 

 induced to grow in symbiosis with other microorganisms. 



BACTERIOLOGICAL EXAMINATION OF OYSTERS 



On account of the danger of the transmission of typhoid fever 

 by oysters which have been bred or stored in contaminated water, 

 standard methods 69 have been devised for the estimation of the 

 bacterial content of oysters. These are similar in principle and 

 method to those used for the examination of water, and a most 

 important index of sewage contamination and consequent danger 

 of typhoid infection is the number of colon bacilli present in the 

 shell fish. The shell liquor is used for examination, and in examining 

 oysters in the shell the following procedure is followed : Five oysters 

 having deep bowls and closed shells are selected. Lips of the shell 

 are sterilized in the flame or by burning with alcohol. The liquor 

 is obtained by opening the shell with a sterilized knife, or better, 

 by drilling a hole through the flame surface with a sterilized gimlet. 

 For determining the total number of bacteria the shell liquor is with- 

 drawn with a sterilized pipette, diluted with 1 per cent salt solution, 

 and placed in agar. More important, however, is the presumptive 

 colon test, which is carried out by inoculating three lactose bile 

 tubes with 1.0 c.c., 0.1 c.c., and 0.1 c.c., respectively, from each of 

 the five oysters. The tubes are incubated for three days, and the 

 development of over 10 per cent of gas in the closed arm is con- 

 sidered a positive reaction. The score is recorded as the approximate 

 number of colon bacilli contained in the 5.55 c.c. of shell liquor 

 from the five oysters, and is estimated in the following way: A 

 positive reaction in a tube inoculated in 1 c.c. is recorded as 1.0, 

 a positive reaction in 0.1 c.c. is 10, and in 0.01 is recorded as 100. 

 The sum of these figures is the score for the batch of oysters from 

 which the five have been taken. In examining shucked oysters a 

 well-mixed sample of oysters and the surrounding fluid are put in 

 a sterilized vessel and lactose bile tubes inoculated in triplicate 

 with 1.0 c.c., 0.1 c.c., 0.01 c.c., 0.001 c.c. of the liquor. No definite 

 standard score has been adopted, but the United States Pure Food 

 Board has condemned unshucked stock having a score of 32 or 

 higher. 



69Amer. Jour. Pub. Health, 1913, ii, 34. 



