
6.5% salt and in the presence of 0.4% sodium azide,
can be identified presumptively as enterococci. This
genus was previously grouped within Streptococcus.
Certainly all the classical species of Enterococcus fall
into this category, but some newly described species
have some aberrant properties which has resulted in
the unofficial division into five subgroups. Several
species of Enterococcus are naturally found in the
intestinal tract of humans and animals. The role of
enterococci in food is unclear and much debated.
These organisms have been isolated from many indi-
genous fermented foods, but their possible positive
contribution has not been elucidated since such prod-
ucts commonly contain several species of LAB. The
tolerance of members of the genus for extremes of
pH, salt, and temperature makes their survival in
fermented foods unproblematic. The fecal original
of many species, such as E. faecalis and E. faecium,
however, means that their presence in foods is
regarded as being an indication of poor hygiene. Fur-
ther complications are the opportunistic pathogeni-
city of some species of Enterococcus, their ability
to decarboxylate amino acids and thereby produce
amines in foods, and finally their propensity to be
resistant to antibiotics and to transfer such traits by
means of mobile genetic elements. A new area of
debate concerns the advisability of using these organ-
isms as probiotics.
The Genus
Leuconostoc
0012 All leuconostocs are heterofermentative cocci. Their
main habitat is on plants and, to a lesser extent, in
meat, milk, and dairy products. As in other genera of
LAB, the member species in this genus are continually
being revised, but this is a comparatively small genus,
with about 11 species. The most common species are
Leuconostoc mesenteroides, which has three subspe-
cies: mesenteroides, cremoris,anddextranicum, and
Leuc. lactis. Several other species at present placed in
the genus Leuconostoc show poor genotypic hom-
ology with the above species, and also with each
other. Leuconostocs play an important role in the
early stages of the fermentation of vegetable products
such as dill pickles, olives, and sauerkraut. They take
over from the initial, mainly Gram-negative flora and
are important for the development of the characteris-
tic flavor of the products. Later in the fermentation
other more aciduric LABs dominate.
0013 Several leuconostocs produce extracellular poly-
saccharides which can be used as food-thickening
agents or stabilizers. However, these dextrans cause
problems in sugar factories and also in fermented
sausages, where the production of slime is undesir-
able. Some mesophilic dairy starter cultures con-
tain leuconostocs. They produce flavor compounds
(diacetyl and acetate) from the metabolism of citrate
and reduce acetaldehyde to ethanol. In addition, pro-
duction of CO
2
from both citrate and carbohydrates
is important for the eyes in Gouda-type cheeses and
the slight effervescence in cultured buttermilk.
The Genus
Oenococcus
0014Oenococcus oeni (previously Leuconostoc oenos)is
the only member of this new genus. It is found in wine
and is responsible for the malo-lactic fermentation
which occurs during the maturation of wine. O.
oeni converts l-malic acid to l-lactic acid, thus in-
creasing the pH by 0.1–0.3 pH units, and rendering
the wine microbiologically stable. Traditionally pre-
sent as a natural contaminant in wine, this organism
may be purposely introduced to some wines to insure
the desired maturation.
The Genus
Lactobacillus
0015Members of the genus Lactobacillus are rod-shaped
and number over 60 species. Despite the fact that
several species have recently been removed to two
new genera (Weissella and Carnobacterium), the
genus is still heterogeneous. Lactobacilli are found
in a variety of habitats and vary considerably in
their characteristics. In 1919, Orla-Jensen grouped
the lactobacilli into three subgenera: Thermobacteria,
Streptobacteria,andBetabacteria. These subgenera
are currently not taxonomically valid, but this sub-
division is still useful to divide the genus into three
primary phenotypic groups: the obligately homo-
fermentative; the facultatively heterofermentative;
and the obligately heterofermentative.
0016Lactobacilli are naturally found in nutritive and
carbohydrate-rich habitats such as plants or material
of plant origin, meat, milk, and dairy products. They
are also found in manure, silage, and sewage. The
mucous membranes (intestinal, vaginal, and oral) of
humans and animals are often dominated by lacto-
bacilli, where they are thought to have a probiotic
function. (See Microflora of the Intestine: Probiotics.)
0017In the food industry, lactobacilli may be respon-
sible for the desired fermentation of some products
but also for the spoilage of others. In dairy foods, Lb.
delbrueckii ssp. bulgaricus is used as a starter culture
for yogurt and a variety of cheeses, particularly
those manufactured using a high cooking tempera-
ture. During the ripening of most cheeses, so-called
‘non-starter’ lactobacilli (NSLAB) develop and are
important for the development of the cheese flavor.
Present research focuses on identifying useful strains
with the prospect of greater control over cheese
ripening. Heterofermentative lactobacilli may cause
unwanted openness in some cheeses due to CO
2
production from residual carbohydrate.
LACTIC ACID BACTERIA 3469