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Thread: Colony growing on top of HLP tube and other weird results.

  1. #1
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    Colony growing on top of HLP tube and other weird results.

    I'm in the unfortunate situation of dealing with several batches in a row going sour. We have acquired the HLP testing media and started testing some past and new batches expecting (almost wanting) to see the infamous teardrops on them. To our dismay, most results have fallen in the ambiguous "it might have LAB, it might not" conclusion.

    Only one of the batches revealed Pediococcus damnosus convincingly. Some have clear looking tubes, but a white fluffy colony covers the top of the liquid. As far as I know, it can't be fungal since the cicloheximide is there to supress eukariote grow; however, Acinetobacter doesn't seem likely since none of the batches tasted like vinegar:

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    Other went full turbid, but have no discernible colonies:

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    Got to say that even the blanks form some sort of insoluble flocs that float around of variable size. Is there a guide somewhere to interpret these weird results? Particularly the veil colony of the top, since those batches doesn't taste bad... yet.

  2. #2
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    That completely hazy tube could be a very contaminated sample. Try that same sample again, just with a small fraction of the volume added to an HLP tube.

    The growth on the top of the tube could certainly be acetobacter. See if you can loop some and wet mount some of them on a slide. Alternatively, you could also try and grow it up in a small amount of wort. Regardless, I think you can rule out LAB here, LAB would never show up like that on HLP.


    Overall, I'm not sure you've found the source of the contamination yet. Try taking more samples upstream.
    Last edited by AT-JeffT; 03-08-2019 at 10:39 AM.

  3. #3
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    Yeah we suspect of our heat exchanger, which we sterilized via heat before putting it on service again and we are sampling right after it.

    Can you tell me your opinion on one more tube?

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    Sample is on the left, blank on the right (that white point on the blank is outside the tube). Both have this small white flocs. Are they an artifact (unsolubilized media) or some microorganism?

    If I test a bottled beer, is 1 UFC / mL sensitive enough to rule off contamination or are lower concentrations still able to sour a beer on a reasonable amount of time (i.e. 6 months)? (EDIT: just read the last thread, will take the answers from there).
    Last edited by javert; 03-08-2019 at 01:18 PM.

  4. #4
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    Minor following.

    A client approached us wanting to confirm whether a probiotic had Lactobacillus plantarum on it or not so we used the HLP media at various dilutions to see if colonies could grow. Low story short, the Lacto behaved as expected: white, turbid samples at early dilutions of the sample, zero at very diluted samples and some textbook teardrops in the middle one:

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    We tested the turbid samples and got ourselves the comet like colonies of Pediococcus:

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    Welp at least we got the two cases there for comparison. We've modified some sanitization procedures for the chiller system and have been doing some forced wort tests. Hopefully they come all right.

  5. #5
    Join Date
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    Quote Originally Posted by javert View Post
    Minor following.

    A client approached us wanting to confirm whether a probiotic had Lactobacillus plantarum on it or not so we used the HLP media at various dilutions to see if colonies could grow. Low story short, the Lacto behaved as expected: white, turbid samples at early dilutions of the sample, zero at very diluted samples and some textbook teardrops in the middle one:

    Name:  IMG_20190402_162653363.jpg
Views: 112
Size:  42.0 KB

    We tested the turbid samples and got ourselves the comet like colonies of Pediococcus:

    Name:  IMG_20190402_162745621.jpg
Views: 112
Size:  54.4 KB

    Welp at least we got the two cases there for comparison. We've modified some sanitization procedures for the chiller system and have been doing some forced wort tests. Hopefully they come all right.

    Sorry I took so long to respond, I must not have subscribed to the thread.

    I'd say those two tube above are not the source of your issue. I would expect the source of your issue to look very much like the textbook middle dilution you have.

    Creating positive tests to compare your results against is very helpful. Remember you can always go grab a sample of stagnant drain water or your own spit will often contain LAB.
    Last edited by AT-JeffT; 04-03-2019 at 10:45 AM.

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