Lactobacillus organisms are specific to lactose in milk, producing lactic acid from the lactose. They aren't a general antibacterial. And if there's no lactose in the medium (ie the wet food), they won't produce any antibacterial activity at all.
(emphasis added)
from: http://en.wikipedia.org/wiki/LactobacillusThe production of lactic acid makes its environment acidic which inhibits the growth of some harmful bacteria
(emphasis added)