Fundamental Food Microbiology, Third Edition - Fuad Fathir

132 FUNDAMENTAL FOOD MICROBIOLOGY
They have been isolated from feces of humans, animals, and birds and are
considered beneficial for the normal health of the digestive tract. They are present
in large numbers in the feces of infants within 2 to 3 d after birth, and usually present
in high numbers in breast-fed babies. They are usually found in the large intestine.
Many species of this genus have been isolated from the feces of humans and
animals. Some of these include Bifidovacterium bifidum, Bif. longum, Bif. brevis,
Bif. infantis, and Bif. adolescentis. All have been isolated in humans; however, some
species are more prevalent in infants than in adults. Some of these species have been
added to dairy products to supply live cells in high numbers to restore and maintain
intestinal health in humans.
B. Propionibacterium
The genus includes species in the classical or dairy propionibacterium group and
the cutaneous or acne propionibacterium group. Here, only the diary group is discussed.
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The cells are Gram-positive, pleomorphic thick rods 1 to 1.5 mm in length, and
occur in single cells, pairs, or short chains with different configurations. They are
nonmotile, nonsporulating, anaerobic (can also tolerate air), catalase positive, and
ferment glucose to produce large amounts of propionic acid and acetic acid. They
also, depending on the species, ferment lactose, sucrose, fructose, galactose, and
some pentoses. They grow optimally at 30 to 37ºC. Some species form pigments.
They have been isolated from raw milk, some types of cheeses, dairy products, and
silage.
At present, four species of diary propionibacterium are included in the genus:
Propionibacterium freudenreichii, Pro. jensenii, Pro. thoenii, and Pro. acidipropionici.
All four are associated with natural fermentation of Swiss-type cheeses, but
Pro. freudenreichii has been used as a starter culture in controlled fermentation.
C. Brevibacterium
The genus contains a mixture of coryniform bacterial species, some of which have
important applications in cheese production and other industrial fermentations.
Brevibacterium linens is used in cheese ripening as it has extracellular proteases.
The cells are nonmotile, Gram-positive, and capable of growing in high salt and
wide pH ranges.
D. Acetobacter
A species in this genus, Ace. aceti, is used to produce acetic acid from alcohol. 2 The
cells are Gram-negative; aerobic; rods (0.5 to 1.5 mm); occurring as single cells,
pairs, or chains; and can be motile or nonmotile. They are obligate aerobes, catalase
positive, and oxidize ethanol to acetic acid and lactic acid to CO 2 and H 2O. They
grow well from 25 to 30ºC. They are found naturally in fruits, sake, palm wine,
cider, beer, sugar cane juice, tea fungus, and soil. Some species synthesize large
amounts of cellulose. 2