Is it a weak or strong activity?   Did you remember to neutralize or desalting your eluate?

The best option is that you are concentrating a  weak G-  activity,  either belonging to the original compound or to another molecule

I'm reading, perhaps incorrectly, that you are seeing activity for gram negative after using the resin but this activity isn't present in your original extract?

You may consider running the cation beads with a blank (distilled or deionized water) to confirm this new activity isn't the result of something on your beads such as a preservative or something else. Follow the same procedure as you did for your extract and test the fractions in the same manner. I once almost went down a blind alley from a preservative in a resin, but my boss recognized the elution time and warned me such that I didn't waste much time.

It is possible that you concentrated an active compound sufficiently to see the activity too, as  indicated by Ameriga.

My dear friend:  Lets go back to our basic microbiology class. We have been taught that Gram positive bacteria, no doubt, have negative charge on their cell wall, but the dipole moment is much weaker than that of most of the gram negative bacteria.  the product after extraction using anionic beads is matching with that dipole moment and that is why you are seeing a more significant activity with gr+ bacteria as compared with gr- bacteria. The dipole moment becomes stronger when you are using  cation beads and that is what is giving you activity against both the types of bacteria.

Jack Silver I see the activity for both gram negative and positive when testing the crude fermentation broth, but the anion beads give activity against gram positive only after using them for extraction.  Jai Ghosh thank for the microbiology lesson/ reminder it now makes senses.