To answer your question:
>Please help!!! Does anyone know an example of a fermentation reaction
>carried out by any bacterium?
The classic definition of fermentation is metabolism that uses an organic
molecule as the terminal electron acceptor rather than oxygen of some other
inorganic molecule (e.g. a mineral). That is, an organic acid is formed
rather than water from oxygen.
Glycolysis is a fermentative pathway of reactions that occurs widely in
bacteria (including E. coli) that produces organic acids (acetate, lactate,
pyruvate, formate & others). These build up in the medium when oxygen is
limiting and oxidative phosphorylation cannot function to reduce oxygen to
water as a more energy efficient way of disposing of electrons.
I hope this answers your question.