A Contribution to the Bacteriology of Milk

Abstract

With ordinary care and cleanliness it is possible to obtain milk which, when freshly drawn, contains less than 1500 organisms per cubic centimetre.Freshly drawn milk should not contain gas-forming organisms in at least 50 c.c.Gas-forming organisms are present in milk owing to contamination with faecal material. Of these organisms the B. oxytocus perniciosus, the B. neapolitanus and the B. coli communis occur in greatest number in fresh milk, while the B. cloacae and B. lactis aerogenes appear at a later stage.Out of 107 non-chromogenic lactose fermenters isolated from milk only one bacillus gave the reactions of the B. acidi lactici (Hüppe); while the B. Grünthal, B. pneumoniae (Friedländer), and the B. coscoroba have not been met with once.Finally, I desire to enter a plea for the substitution of certain fermentation reactions in the place of some of the tests now usually employed, in the routine examination of water and food-stuffs, to identify these organisms. At present bacteriologists make use of some, or all, of the following tests:1. Morphology.2. Motility.3. Staining by Gram's method.4. Character of the growth on nutrient gelatin.5. Liquefaction of gelatin.6. Action on milk.7. Foemation of indol.8. Fermentation of glucose.9. Fermentation of lactose.10. Fermentation of cane sugar.11. Action on neutral-red.All the organisms mentioned in Tables I and II produced clotting in milk, fermented glucose, gave the neutral-red reaction, had much the same morphology, and the growths on agar and gelatin did not afford any assistance towards differentaniting between them.I would therefore suggest that instead of five of the tests, Nos. 4, 6, 7, 8, and 11, we should substitute the following:Fermentation of dulcit,Fermentation of adonit,Fermentation of inulin,Vodes and Proskauer's reaction, as by so doing we should get a finer differentiation without increase in work and we should not be classing as B. coli organisms which may have little in common with, and have a distribution entirely different from that of the B. coli communis.