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© 1993, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension. All rights reserved.


Bacterial contamination reduces the quality of milk and can cause serious health problems. This NebGuide discusses common causes of contamination as well as prevention.

Bacteria are single-cell organisms that multiply by dividing to form two cells (a process known as mitosis). Under optimum conditions, many bacteria can double in number each 20 minutes. That means one bacterium can result in up to 16,000,000 bacteria in just eight hours. They are microscopic in size, i.e., an individual bacterium cannot be seen without the aid of a microscope. They are so small that a single drop of water from a cow's udder might contain up to 30 billion (30 with nine zeros!) bacteria.

Bacteria are part of our everyday world. Given the different genus, species and strains, literally thousands of bacteria have been identified.