The genus Lactobacillus was proposed by Beijerinck
in 1901 (14). Since then, many species have been described
but either not validated or, as mentioned above, shown
to be homologous to existing species. Examination of the presence
of fructose-1,6-bisphosphate aldolase resulted in the subdivision
of these bacteria into three physiological groups: (i)
the obligately homofermentative lactobacilli, (ii) the facultatively
heterofermentative species, and (iii) the obligately heterofermentative
species which lack fructose-1,6-bisphosphate
aldolase. Although correct classification and identification of
lactic acid bacteria are difficult without the support of modern
genotypic techniques (see above), the large number of species
renders an exclusively genotypic approach quite cumbersome.
Therefore, fermentation reactions (mostly examined via commercially
available test systems) remain important as tools for
identification and classification.