Speaking as a vegan, I would not condemn eating jellyfish. Of course, I would not eat jellyfish, but if doing so is what contributes to the happiness of the eater, I have no inclination to condemn the behavior.

Regarding bacteria, my choice to be vegan is based on the lifestyle’s contribution to my commitment to live as healthfully as possible while causing the least suffering possible. When bacteria negatively impact that commitment I will respond to mitigate that impact. The same would be true as it regards jellyfish. The response would not include condemnation, anger or any other circumstance that may result in an unnecessarily severe response.

A practice that I find practical when considering the least harmful, but most effective response to situations that intentional influence the life of other beings is one I call "The Agreement". The practice can be illustrated thus: I enjoy tending to several flower beds around our home. Those beds often have unintended weeds popping up in their soil. Before removing the uninvited plants I say to them "We have an agreement - I will do my best not to negatively impact you in your habitat outside my yard and garden. In return, you will limit your influence on me by thriving only outside my yard and garden. You have violated our agreement and thus I am going to remove you from this soil".

As is often stated here, I can not take a breath without impacting and potentially harming another being. The goal in my vegan lifestyle is not to achieve the impossible and cause no harm, but to approach each day with intention to cause the least harm and suffering possible. That intention includes not condemning others for their choices.