New Bacteria Found in Raw Milk
Raw milk, illegal to sell in many countries, can be contaminated with harmful bacteria. This contamination could spoil the milk, which turns it thick, sticky and tasting bitter. A new species of bacteria has been found in raw milk and it can grow at low temperatures, even spoiling the raw milk when it is refrigerated.
"When we looked at the bacteria living in raw milk, we found that many of them had not been identified before," said Dr Malka Halpern from the University of Haifa, Israel. "We have now identified and described one of these bacteria, Chryseobacterium oranimense, which can grow at cold temperatures and secretes enzymes that have the potential to spoil milk."
"Milk can be contaminated with many different bacteria from the teat of the cow, the udder, milking equipment and the milking environment," said Dr Halpern. "Milk is refrigerated after collection to limit the growth of microbes. During refrigeration, cold-tolerant, or psychrotolerant, bacteria that can grow at 7°C dominate the milk flora and play a leading role in milk spoilage. Although we have not yet determined the impact on milk quality of C. oranimense and two other novel species (C. haifense and C. bovis) that were also identified from raw milk samples, the discovery will contribute to our understanding the physiology of these organisms and of the complex environmental processes in which they are involved. There is still a lot to learn about the psychrotolerant bacterial flora of raw milk."
Some people believe that raw milk has health benefits and that it is worth the risk of ingesting potentially harmful bacteria. These people think pasteurization should be done away with altogether. Pasteurization involves heating the milk to 160 degrees Fahrenheit for about 15-20 seconds in order to get rid of harmful bacteria.
"In Israel, dairy companies estimate that cold-tolerant bacteria can cause a 10% loss of milk fats and proteins. When researchers looked at these bacterial communities, they found that 20% of the bacteria isolated were found to be novel species and 5% of these were members of the genus Chryseobacterium," said Dr Halpern. "Because of their effect on milk quality, it is important that we develop sensitive and efficient tools to monitor the presence of these cold-tolerant bacteria."
While raw milk is available in some areas, many places have made it illegal to sell. For the places that do sell raw milk, a special warning label is placed on the container stating that the product has not been heat-treated and may contain harmful organisms.
This research was published in the November issue of the International Journal of Systematic and Evolutionary Microbiology.