Staph infection of milk questions

[scasnerkay]

The cow that I get milk from, is tested quarterly by a vet for what might be growing in her udder/milk. Her most recent test, from milk collected 2 weeks ago, is positive for Staphylococcus warneri, and for S. xylosus. I have been drinking the milk for much longer than the 2 weeks, with no ill effects. And others who work at the farm and take home milk have also been fine. I drink the milk at my own risk, but I am concerned about the cheeses I have been making. I age all the cheeses more than 2 months. Is that long enough for the positive bacteria to out-compete the bad guys? Is there a way to tell if the cheeses I have made are safe to eat? Of course I do not sell the cheese, but sometimes I trade with neighbors, and certainly all my family eat the cheese...

[Sailor Con Queso]

Those Staph species are not the most virulent around, but can cause meningitis and urinary tract infections. Staph produces an exotoxin, meaning it is produced in the food, not in your body, so actual infection by the bacteria may not be necessary in order to get sick. Aging may or may not allow good bacteria to out-compete the Staph so professionally I would recommend that you pitch everything that you have made since the infection showed up. To me, it would not be worth the risk. You can always make more cheese. The problem is with quarterly vet testing, the bacteria may have been present for a while.

So, that being said, here are some other things to consider. Licensed Grade A dairy farmers have to test for "somatic cell count". Increased somatic cells in milk are a pretty good indication that an infectious disease MAY be starting in the cow. When the somatic cell count is too high, dairy farmers are not allowed to legally sell milk. Do you or the farmer test for somatic cells? If so, how has the count been looking? Were the cows showing any signs of illness? I would also like to know how the bacterial testing was done. Did the Staph show up in actual milk samples or was this from an external swab of the cow's udders? Was the positive test from a single animal or a mixed "pool" of sampling? What was the viable colony count of the positive test? Small count = small infection. Big Count = bigger infection.

Staph is everywhere and was most likely picked up externally at the teats rather than being an actual infection. If that is the case, either you or the farmer might need to work on better sanitation during milking. If the bacteria showed up as a result of external swabs, the vet might need to work on better sanitation during specimen collection.

[Sailor Con Queso]

One other point. Milk that is slightly contaminated might be perfectly safe to drink because the bacteria are at "sub-clinical" levels. However, when you warm that milk to cheese making temperatures, you create the perfect environment for those contaminants to multiply.

[scasnerkay]

Thank you Sailor. My thoughts exactly about making the cheese versus drinking the milk. Since I can use it only for my family, I may assume the risk of eating some.
This is just one cow at the farm. The "farmer," a city employee, randomly does a CMT for somatic count. Somatic cell count seems like a piece of information that should be on the report from the vet. The farmer is on vacation for 2 weeks, so I will try the CMT tomorrow out of curiosity.
The cow shows no signs of illness, her udder looks normal, the initial milk into the strip cup looks fine with no clotting, streaking or blood and the pH is the same as always on her milk.