Dear S.H. Ramaprasad, 

the term mutation refers to alterations in DNA sequence. And it depends on the nature of the mutation, if the mutation produce a change in amino acid, these radical changes are many times involved in changes in phenotype, by protein destabilisation/loss of function/neofunctionalization/subfunctionalization

When your organism acquire a single mutation, you can expect that these organism is a mutant, but you should also consider that bacteria usually form populations, and populations have genetic polymorphism, so you should be aware to not confuse mutant with a genetic variant.

Did you mean with "real bacterial mutants" that the mutation confers a new phenotype? 

There's a lot of literature on adaptive mutations in bacteria and the arose of mutants check for Richard Lenski and his 50.000 generations experiment; or those from Mario A. Fares in bacteria and yeast (with myself as co-author).