What you are observing is not contaminant. In all probability, it must be a probiotic spore forming Gram positive Lactobacillus spp.

Bacillus licheniformis?

Prob a Bacillus sp. - can't distinguish species on the small amount of info offered. Bergey's defines genus Lactobacillus as non spore forming.

Here's link to some Bacillus spp. colony morphologies.

http://flora-jg.de/eos20d/cultures2.html

To Jai's point - what is colony morphology of your "probiotic" isolate? Could it be a mixed culture (or the probiotic itself) and the source of your issue?

No Phil....There is atleast one species of Lactobacillus which forms spore and that is Lactobacillus sporogenes (given often directly to patients who have a highly imbalanced gut flora due to some reason or the other).

thanks Jai - the genus description was Bergey's and it's Bacillus coagulans in the 7th ed.

I understand many, esp. in probiotic field, refer to the bacterium as Lactobacillus sporogenes Horowitz­Wiassowa and Nowotelnow - the 1932 species is apparently an illegitimate binomial. I understand the correct taxonomy for this bacterium is Bacillus coagulans. I refer you to the ATCC https://www.atcc.org/Search_Results.aspx?dsNav=Ntk:PrimarySearch%7clactobacillus+sporogenes%7c3%7c,Ny:True,Ro:0,N:1000552&searchTerms=lactobacillus+sporogenes&redir=1 as well as the linked descriptions Article Should Lactobacillus sporogenes and Bacillus coagulans Have a Future?

and http://www.food-info.net/uk/ff/sporogenes.htm

.

Thank you so much for all of your comments. Sorry for the long delay, end of semester is alway a busy time.

We have been running this lab once a semester for a long time, and use common grocery store brands as our test agents. We use several different brands with a variety of species in each, and are consistent with the brands/varieties that we use each semester.

This new colony that we observed this semester has not been seen before and was not consistent in its presence. Some students had only 1 plate out of 8 contaminated, others would have none or all contaminated. Out of students that used the same original sample, some would have contamination and some would not. This made us assume that we had a contamination.

The cultures that have been suggested in the comments are not cultures that we have or have had in the past in our labs, or listed as cultures in our original samples.

We have fully cleaned and tested all possible sources of contamination. How could this kind of contamination be so virulent in the lab but then not be present anywhere afterward? Could the source of contamination come from the original sample? Even if our samples are within the expiration period and stored properly.

Thank you for your attention

Suppose the isolate could have come from the product. Looks like a Bacillus sp. - might be a lab or product contaminant but B. coagulans is considered a probiotic bacterium. Was it recovered from only one brand, one package?

Inconsistent isolation - not much to offer. I;m aware counts in some commercial yogurts are not very stable.

Thank you for your response. My last thought for its presence is within the product. I am discarding our old samples and purchasing new! Hopefully we do not experience this again this semester!!

Lactobacillus sps. are basically non sporeformers. There are some sporeforming bacillus sp. also used being used as probiotics, and one is Bacillus coagulans, as suggested by Dr. Phil Geis. If the product's labelling do not say anything about the type of probiotic strains used, it should be considered as a secondary contamination during handling. Please try with new samples of the same product.