[TOMT] [TV Show or Story] A newlywed couple encounter mold on a boat, husband taken over by mold.

A little background:

My girlfriend and I have been looking for the origin of this story since we first met ten years ago. She was told this story by her mother, who in turn was told by her mother (gf's grandma) when she was a child (late 50'/60's). Gf's mom remembers being told that it was a Twilight Zone episode. But our search through every episode description yielded nothing.

Here's the story as she remembers:

"A newlywed couple leave for their honeymoon on their new houseboat. As soon as they board the boat, they notice a strange mold/slime. They set sail, and get to work cleaning their new boat. However, they begin to notice something strange, whenever they clean the mold, it seems as if more appears. The husband sends the wife back to shore to get some stronger cleaning supplies. She heads back to the boat that evening and is shocked to see that they mold has completely covered the boat. She hears her husband's voice yelling out to her to turn around and leave. She does so and her husband yells out, instructing her not to look back. The wife does not listen and turns back to look for her husband. She doesn't see her husband, but instead catches a glimpse of a human shaped lump of mold, which stoops dejectedly when she looks back. She realizes that the mold/slime has consumed her new husband."

For 10 years, we've skimmed episodes descriptions of every mystery/science fiction anthology series from the 50's/60's we could find. Outer Limits, Alfred Hitchcock Presents, Thriller... But we've never come across anything resembling the story. At this point, we've come to the conclusion that it probably wasn't even something her grandma saw on television, but most likely a short story she read somewhere. Does anyone recognize this from anywhere?