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The Physiological Types of Bacteria in Milk in Relation to Reduction of Methylene Blue

University of Arizona

ABSTRACT

1. Over 1,000 milk samples were studied for physiological types of bacteria present in relation to reduction time of methylene blue.
   
2. The samples studied were shown to contain on the average of 6.27 percent acid-coagulating bacteria, 55.82 per cent acid-not-coagulating, 11.59 per cent acid-coagulating-gas-proteolytic, 16.56 per cent acid-proteolytic, 2.28 per cent alkaline, 2.83 per cent inert bacteria and 4.25 per cent of our tubes were blank.
   
3. There is a wide seasonal variation in physiological types of bacteria in milk.
   
4. Acid-not-coagulating bacteria are poor reducers of methylene blue but are predominant in most high quality milk.
   
5. Proteolytic types of bacteria are good oxygen absorbers and play an important part in reduction.
   
6. There is an associative action between bacteria which usually overshadows individual variations of reduction power.
   
7. Marked variations in physiological types of bacteria present in individual samples failed to have any material effect on reduction time.
   
8. Acid-coagulating, alkaline and inert bacteria seem to have no special effect on reduction rates, unless present in unusually large numbers.