Japanese nickname confusion

So, I'm "reading" a manga with a main character named Yamaguchi Kensuke (山口建介). His nickname is YamaKen (ヤマケン), which makes sense from what I know of Japanese nicknames -- so far so good. But some less-than-nice people call him YamaKin (ヤマ菌), and that's where my confusion lies. Kin means germ or bacteria, I believe, and yama can mean mountain... So are they basically calling him a huge pile of bacteria? Or is it just a punny way of saying Germy Yama or whatever?