The Germ

From Muppet Wiki

The Germ (or, more specifically, streptococcus yuckotherium) appears in the Muppet Labs sketch in episode 307 of The Muppet Show. When Beaker adds one drop of Bunsen's Germ Enlarger to the petri dish holding the deadly Germ, it grows so large that it proceeds, inevitably, to consume Beaker as he tries to make his way backstage. The ever-optimistic Bunsen, however, sees this as an opportunity for Beaker to more easily study the Germ...and vice versa. Bunsen is similarly amused by Kermit's concern that the Germ might be contagious.

As recalled by Amy van Gilder in the book Of Muppets and Men, the character was built using cellophane and coat hangers.