Characteristics of Predominant Microorganisms in Food ◾ 25
Pediococcus. Spherical cells (1 μm); form tetrads; mostly present in pairs; nonmotile; facultative
anaerobes; homolactic fermentators; mesophiles, but some can grow at 50°C; some survive
pasteurization. Some species and strains are used in food fermentation. Some can cause
spoilage of alcoholic beverages. Found in vegetative materials and in some food products.
Species: Pediococcus acidilactici and Ped. pentosaceus. Several strains produce bacteriocins,
some with a wide spectrum against Gram-positive bacteria, and they can be used as food
biopreservatives.
Sarcina. Large, spherical cells (1–2 μm); occur in packets of eight or more; nonmotile; produce acid and gas from carbohydrates; facultative anaerobes. Present in soil, plant products, and animal feces. Can be involved in spoilage of foods of plant origin. Species:
Sarcina maxima.
Staphylococcus. Spherical cells (0.5–1 μm); occur singly, in pairs, or in clusters; nonmotile;
mesophiles; facultative anaerobes; grow in 10% NaCl. Staphylococcus aureus strains are frequently involved in foodborne diseases. Sta. carnosus is used for processing some fermented
sausages. Main habitat is skin of humans, animals, and birds.
Streptococcus. Spherical or ovoid (1 μm); occur in pairs or chains; nonmotile; facultative anaerobes; mesophiles. Streptococcus pyogenes is pathogenic and has been implicated in foodborne
diseases; present as commensals in human respiratory tract. Str. thermophilus is used in dairy
fermentation; can be present in raw milk; can grow at 50°C.
Gram-Positive, Endospore-Forming Rods
Bacillus. Rod-shaped, straight cells; vary widely in size (small, medium, or large; 0.5–1 ×
2–10 µm) and shape (thick or thin); single or in chains; motile or nonmotile; mesophiles
or psychrotrophic; aerobes or facultative anaerobes; all form endospores that are spherical
or oval and large or small (one per cell); spores are highly heat resistant. Includes many
species, some of which are important in foods, because they can cause foodborne disease
(Bacillus cereus) and food spoilage, especially in canned products (Bac. coagulans, Bac.
stearothermophilus). Enzymes of some species and strains are used in food bioprocessing
(Bac. subtilis). Present in soil, dust, and plant products (especially spices). Many species
and strains can produce extracellular enzymes that hydrolyze carbohydrates, proteins, and
lipids.
Clostridium. Rod-shaped cells that vary widely in size and shape; motile or nonmotile; anaerobes (some species extremely sensitive to oxygen); mesophiles or psychrotrophic; form endospores (oval or spherical) usually at one end of the cell, some species sporulate poorly, spores
are heat resistant. Found in soil, marine sediments, sewage, decaying vegetation, and animal
and plant products. Some are pathogens and important in food (Clostridium botulinum, Clo.
perfringens) and others are important in food spoilage (Clo. tyrobutyricum, Clo. saccharolyticum, Clo. laramie). Some species are used as sources of enzymes to hydrolyze carbohydrates
and proteins in food processing.
Sporolactobacillus. Slender, medium-sized rods (1 × 4 μm); motile; microaerophilic; homolactic
fermentors; form endospores (spore formation is rare in most media), but the spores are less
heat resistant than Bacillus spores. Found in chicken feed and soil. Importance in food is not
clearly known. Species: Sporolactobacillus inulinus.
Pediococcus. Spherical cells (1 μm); form tetrads; mostly present in pairs; nonmotile; facultative
anaerobes; homolactic fermentators; mesophiles, but some can grow at 50°C; some survive
pasteurization. Some species and strains are used in food fermentation. Some can cause
spoilage of alcoholic beverages. Found in vegetative materials and in some food products.
Species: Pediococcus acidilactici and Ped. pentosaceus. Several strains produce bacteriocins,
some with a wide spectrum against Gram-positive bacteria, and they can be used as food
biopreservatives.
Sarcina. Large, spherical cells (1–2 μm); occur in packets of eight or more; nonmotile; produce acid and gas from carbohydrates; facultative anaerobes. Present in soil, plant products, and animal feces. Can be involved in spoilage of foods of plant origin. Species:
Sarcina maxima.
Staphylococcus. Spherical cells (0.5–1 μm); occur singly, in pairs, or in clusters; nonmotile;
mesophiles; facultative anaerobes; grow in 10% NaCl. Staphylococcus aureus strains are frequently involved in foodborne diseases. Sta. carnosus is used for processing some fermented
sausages. Main habitat is skin of humans, animals, and birds.
Streptococcus. Spherical or ovoid (1 μm); occur in pairs or chains; nonmotile; facultative anaerobes; mesophiles. Streptococcus pyogenes is pathogenic and has been implicated in foodborne
diseases; present as commensals in human respiratory tract. Str. thermophilus is used in dairy
fermentation; can be present in raw milk; can grow at 50°C.
Gram-Positive, Endospore-Forming Rods
Bacillus. Rod-shaped, straight cells; vary widely in size (small, medium, or large; 0.5–1 ×
2–10 µm) and shape (thick or thin); single or in chains; motile or nonmotile; mesophiles
or psychrotrophic; aerobes or facultative anaerobes; all form endospores that are spherical
or oval and large or small (one per cell); spores are highly heat resistant. Includes many
species, some of which are important in foods, because they can cause foodborne disease
(Bacillus cereus) and food spoilage, especially in canned products (Bac. coagulans, Bac.
stearothermophilus). Enzymes of some species and strains are used in food bioprocessing
(Bac. subtilis). Present in soil, dust, and plant products (especially spices). Many species
and strains can produce extracellular enzymes that hydrolyze carbohydrates, proteins, and
lipids.
Clostridium. Rod-shaped cells that vary widely in size and shape; motile or nonmotile; anaerobes (some species extremely sensitive to oxygen); mesophiles or psychrotrophic; form endospores (oval or spherical) usually at one end of the cell, some species sporulate poorly, spores
are heat resistant. Found in soil, marine sediments, sewage, decaying vegetation, and animal
and plant products. Some are pathogens and important in food (Clostridium botulinum, Clo.
perfringens) and others are important in food spoilage (Clo. tyrobutyricum, Clo. saccharolyticum, Clo. laramie). Some species are used as sources of enzymes to hydrolyze carbohydrates
and proteins in food processing.
Sporolactobacillus. Slender, medium-sized rods (1 × 4 μm); motile; microaerophilic; homolactic
fermentors; form endospores (spore formation is rare in most media), but the spores are less
heat resistant than Bacillus spores. Found in chicken feed and soil. Importance in food is not
clearly known. Species: Sporolactobacillus inulinus.