This chapter is meant to (1) review classical methods used to characterize
and classify microbes and (2) introduce new molecular methods used in
microbial characterization. The fundamental composition of microbes is
discussed as well as their importance in classifi cation of microbes into
genus and species. Classical microbiological methods in general seek to
defi ne the common features of specifi c bacterial groups as a means of classifi
cation and identifi cation of microbes. Thus, the focus was to describe the
common features which discriminated closely related groups of organisms.
In contrast, the newer molecular methods often seek to expand the classifi -
cation of microbes not only as a means to organize microbial phylogeny but
also to differentiate signatures between microbes identifi ed within a species
in greater detail. Molecular biology tools are used both as an adjunct to
established methods and as replacement for classical methods for detection,
discrimination, or identifi cation of bacterial and viral species.