26 ◾ Fundamental Food Microbiology
Gram-Negative, Endospore-Forming Rods
Desulfotomaculum. One species important in food is Desulfotomaculum nigrificans. The
medium-sized cells are rod-shaped, motile, thermophilic, strictly anaerobes, and produce
H2S. Endospores are oval and resistant to heat. Found in soil. Cause spoilage of canned
food.
Gram-Positive, Nonsporulating Regular Rods
Brochothrix. Similar in many characteristics to lactobacilli; facultative anaerobes; homofermentative; nonmotile; found in meat. It can grow in refrigerated vacuum-packaged meat and
meat products. Species: Brochothrix thermosphacta.
Carnobacterium. Similar in many characteristics to lactobacilli cells; found in meat and fish;
facultative anaerobes; heterofermentative; nonmotile; can grow in foods, especially in meat
products; stored at refrigerated temperature. Some strains produce bacteriocins. Species:
Carnobacterium piscicola.
Listeria. Short rods (0.5 × 1 μm); occur singly or in short chains; motile; facultative anaerobes;
can grow at 1°C; cells killed by pasteurization. The species are widely distributed in the environment and have been isolated from different types of foods. Some Listeria monocytogenes
strains are important foodborne pathogens.
Lactobacillus. Rod-shaped cells that vary widely in shape and size, some are very long, whereas
others are coccobacilli, appear in single or in small and large chains; facultative anaerobes;
most species are nonmotile; mesophiles (but some are psychrotrophs); can be homo- or heterolactic fermentors. Found in plant sources, milk, meat, and feces. Many are used in food
bioprocessing (Lactobacillus delbrueckii subsp. bulgaricus, Lab. helveticus, Lab. plantarum)
and some are used as probiotics (Lab. acidophilus, Lab. reuteri, Lab. casei subsp. casei). Some
species can grow at low temperatures in products stored at refrigerated temperature (Lab.
sake, Lab. curvatus). Several strains produce bacteriocins, of which some having a wide spectrum can be used as food biopreservatives.
Gram-Positive, Non-Spore-Forming Irregular Rods
Bifidobacterium. Rods of various shapes; present singly or in chains; arranged in V or starlike shape; nonmotile; mesophiles; anaerobes. Metabolize carbohydrates to lactate and acetate. Found in colons of humans, animals, and birds. Some species are used in probiotics
(Bifidobacterium bifidum, Bif. infantis, Bif. adolescentis).
Brevibacterium. Cells can change from rod to coccoid shape; aerobes; nonmotile; mesophiles.
Two species, Brevibacterium linens and Bre. casei, have been implicated in the development
of the aroma in several cheese varieties (surface ripened) because of the production of sulfur
compounds (such as methanethiol). In other protein-rich products, they can cause spoilage
(in fish). They are found in different cheeses and raw milk.
Corynebacterium. Slightly curved rods; some cells stain unevenly; facultative anaerobes; nonmotile; mesophiles; found in the environment, plants, and animals. Some species cause food
spoilage. Corynebacterium glutamicum is used to produce glutamic acid.
Gram-Negative, Endospore-Forming Rods
Desulfotomaculum. One species important in food is Desulfotomaculum nigrificans. The
medium-sized cells are rod-shaped, motile, thermophilic, strictly anaerobes, and produce
H2S. Endospores are oval and resistant to heat. Found in soil. Cause spoilage of canned
food.
Gram-Positive, Nonsporulating Regular Rods
Brochothrix. Similar in many characteristics to lactobacilli; facultative anaerobes; homofermentative; nonmotile; found in meat. It can grow in refrigerated vacuum-packaged meat and
meat products. Species: Brochothrix thermosphacta.
Carnobacterium. Similar in many characteristics to lactobacilli cells; found in meat and fish;
facultative anaerobes; heterofermentative; nonmotile; can grow in foods, especially in meat
products; stored at refrigerated temperature. Some strains produce bacteriocins. Species:
Carnobacterium piscicola.
Listeria. Short rods (0.5 × 1 μm); occur singly or in short chains; motile; facultative anaerobes;
can grow at 1°C; cells killed by pasteurization. The species are widely distributed in the environment and have been isolated from different types of foods. Some Listeria monocytogenes
strains are important foodborne pathogens.
Lactobacillus. Rod-shaped cells that vary widely in shape and size, some are very long, whereas
others are coccobacilli, appear in single or in small and large chains; facultative anaerobes;
most species are nonmotile; mesophiles (but some are psychrotrophs); can be homo- or heterolactic fermentors. Found in plant sources, milk, meat, and feces. Many are used in food
bioprocessing (Lactobacillus delbrueckii subsp. bulgaricus, Lab. helveticus, Lab. plantarum)
and some are used as probiotics (Lab. acidophilus, Lab. reuteri, Lab. casei subsp. casei). Some
species can grow at low temperatures in products stored at refrigerated temperature (Lab.
sake, Lab. curvatus). Several strains produce bacteriocins, of which some having a wide spectrum can be used as food biopreservatives.
Gram-Positive, Non-Spore-Forming Irregular Rods
Bifidobacterium. Rods of various shapes; present singly or in chains; arranged in V or starlike shape; nonmotile; mesophiles; anaerobes. Metabolize carbohydrates to lactate and acetate. Found in colons of humans, animals, and birds. Some species are used in probiotics
(Bifidobacterium bifidum, Bif. infantis, Bif. adolescentis).
Brevibacterium. Cells can change from rod to coccoid shape; aerobes; nonmotile; mesophiles.
Two species, Brevibacterium linens and Bre. casei, have been implicated in the development
of the aroma in several cheese varieties (surface ripened) because of the production of sulfur
compounds (such as methanethiol). In other protein-rich products, they can cause spoilage
(in fish). They are found in different cheeses and raw milk.
Corynebacterium. Slightly curved rods; some cells stain unevenly; facultative anaerobes; nonmotile; mesophiles; found in the environment, plants, and animals. Some species cause food
spoilage. Corynebacterium glutamicum is used to produce glutamic acid.