Have you discussed the ethics and legality of such research with regulatory bodies in your country or with your University's biosafety or bioethics committees? The advisablity of such work is certainly questionable.

Dear Nurshahieda

As per my knowledge lactococci enjoy GRAS Status and are relatively non-pathogenic.

Harsh

if the culture is old then also the pathogenicity may be reduced , keeping in mind the first answer regarding sfety, use 24-48 hr old culture for LC50 test.

Selamat pagi. If the concern is that you want to see a response in your prawn, options could be increasing time of exposure or increasing quantity of cells per mL in your inoculus. By the way, the way you set the question could be missunderstood, my first impression was similar to Dr. Cote. Please be careful with patogens.