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What is the best method to differentiate between Enterococcus faecalis, Enterococcus durans, and Lactococcus lactis? I had no growth at 45C on TSA nor Sheep Blood Agar, but I got a positive test for Idexx Enterolert test (presence or absence of enteroccocus). I have a positive PYRA, but a negative mannitol and sorbitol. I ran a Strep 20E and the results gave me a low discrimination. Any suggestions? Thank you.
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Separating Lactococcus from Enterococcus is tricky. Lactococcus reacts with Group N antisera, which most of us do not have, but they should not react with the Group D antisera. Enterococci will grow at 10 and 45 C, but lactococci will grow at 10 but not at 45 C. You should try these temp tests in broth in a water bath to control the temp and do a positive enterococcus control like the ATCC 29212. Biochemically Lactococcus will resemble E. faecalis (Mann +, Sorbitol +) while E. durans is neg for both. The GenProbe for Enterococcus should not be positive for Lactococcus. What do your susceptibility tests look like? A self-respecting Enterococcus will be resistant to all cephalosporins. Lactococci should appear more susceptible to these agents. If this is very important clinically, send isolate to CDC or get molecular confirmation.
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