Phage - Viruses That Infect Bacteria

[CdnMorganGal]

From the Moorlands Cheesemaking site:   "If making cheese daily, order a mixture of MA4001 and MA4002 and use on alternate days to reduce the risk of phage."

Could someone, in laymans language, explain the risks of phage, how to recognize it, how common is it and how the above procedure reduces the risk?  Thank you.

[smilingcalico]

Bacteriophage are viruses that infect bacteria.  According to Wikipedia, "Phages are estimated to be the most widely distributed and diverse entities in the biosphere."  Cultures are made up of a blend of cultures, so if a bacteriophage attacks one type of culture, the rest will still work.  Then, by using the second blend of cultures, you again are switch up the variety and if there is bacteriophage, it will not be able to take hold and get out of control.  I understand it can cause a huge loss of product, but I've only heard of this once in the last 3 years, but I don't exactly have my finger on the pulse of the dairy industry. 
  I don't know how to recognize it, so I'll let someone more knowledgeable take it from here.