24 ◾ Fundamental Food Microbiology
Shigella. Medium rods; nonmotile; mesophiles. Found in the intestine of humans and primates.
Associated with foodborne diseases. Species: Shigella dysenteriae.
Serratia. Small rods (0.5 × 1.5 μm); motile; colonies white, pink, or red; some grow at refrigerated temperature. Occur in the environment. Cause food spoilage. Species: Serratia
liquefaciens.
Yersinia. Small rods (0.5 × 1 μm); motile or nonmotile; can grow at 1°C. Present in the intestinal contents of animals. Yersinia enterocolitica has been involved in foodborne disease
outbreaks.
Vibrio. Curved rods (0.5 × 1.0 μm); motile; mesophiles. Found in freshwater and marine environments. Some species need NaCl for growth. Several species are pathogens and have been
involved in foodborne disease (Vibrio cholerae, Vib. parahaemolyticus, and Vib. vulnificus),
whereas others can cause food spoilage (Vib. alginolyticus).
Rickettsia
Coxiella. Gram-negative; nonmotile; very small cells (0.2 × 0.5 μm); grow on host cells.
Relatively resistant to high temperature (killed by pasteurization). Coxiella burnetii causes
infection in cattle and has been implicated with Q fever in humans (especially on consuming unpasteurized milk).
Gram-Positive Cocci
Enterococcus. Spheroid cells (1 μm); occur in pairs or chains; nonmotile; facultative anaerobes;
some strains survive low heat (pasteurization); mesophiles. Normal habitat is the intestinal
contents of humans, animals, and birds, and the environment. Can establish on equipment
surfaces. Used as an indicator of sanitation. Important in food spoilage. Species: Enterococcus
faecalis.
Lactococcus. Ovoid elongated cells (0.5–1.0 μm); occur in pairs or short chains; nonmotile;
facultative anaerobes; mesophiles, but can grow at 10°C; produce lactic acid. Used to produce many bioprocessed foods, especially fermented dairy foods. Species: Lactococcus lactis
subsp. lactis and subsp. cremoris; present in raw milk and plants, and several strains produce
bacteriocins, some with a relatively wide host range against Gram-positive bacteria and have
potential as food biopreservatives.
Leuconostoc. Spherical or lenticular cells; occur in pairs or chains; nonmotile; facultative anaerobes; heterolactic fermentators; mesophiles, but some species and strains can grow at or
below 3°C. Some are used in food fermentation. Psychrotrophic strains are associated with
spoilage (gas formation) of vacuum-packaged refrigerated foods. Found in plants, meat, and
milk. Species: Leuconostoc mesenteroides subsp. mesenteroides, Leu. lactis, Leu. carnosum; Leu.
mesenteroides subsp. dextranicum produces dextran while growing in sucrose. Several strains
produce bacteriocins, some with a wide spectrum against Gram-positive bacteria, and these
have potential as food biopreservatives.
Micrococcus. Spherical cells (0.2–2 μm); occur in pairs, tetrads, or clusters; aerobes; nonmotile;
some species produce yellow colonies; mesophiles, resistant to low heat. Found in mammalian skin. Can cause spoilage. Species: Micrococcus luteus.
Shigella. Medium rods; nonmotile; mesophiles. Found in the intestine of humans and primates.
Associated with foodborne diseases. Species: Shigella dysenteriae.
Serratia. Small rods (0.5 × 1.5 μm); motile; colonies white, pink, or red; some grow at refrigerated temperature. Occur in the environment. Cause food spoilage. Species: Serratia
liquefaciens.
Yersinia. Small rods (0.5 × 1 μm); motile or nonmotile; can grow at 1°C. Present in the intestinal contents of animals. Yersinia enterocolitica has been involved in foodborne disease
outbreaks.
Vibrio. Curved rods (0.5 × 1.0 μm); motile; mesophiles. Found in freshwater and marine environments. Some species need NaCl for growth. Several species are pathogens and have been
involved in foodborne disease (Vibrio cholerae, Vib. parahaemolyticus, and Vib. vulnificus),
whereas others can cause food spoilage (Vib. alginolyticus).
Rickettsia
Coxiella. Gram-negative; nonmotile; very small cells (0.2 × 0.5 μm); grow on host cells.
Relatively resistant to high temperature (killed by pasteurization). Coxiella burnetii causes
infection in cattle and has been implicated with Q fever in humans (especially on consuming unpasteurized milk).
Gram-Positive Cocci
Enterococcus. Spheroid cells (1 μm); occur in pairs or chains; nonmotile; facultative anaerobes;
some strains survive low heat (pasteurization); mesophiles. Normal habitat is the intestinal
contents of humans, animals, and birds, and the environment. Can establish on equipment
surfaces. Used as an indicator of sanitation. Important in food spoilage. Species: Enterococcus
faecalis.
Lactococcus. Ovoid elongated cells (0.5–1.0 μm); occur in pairs or short chains; nonmotile;
facultative anaerobes; mesophiles, but can grow at 10°C; produce lactic acid. Used to produce many bioprocessed foods, especially fermented dairy foods. Species: Lactococcus lactis
subsp. lactis and subsp. cremoris; present in raw milk and plants, and several strains produce
bacteriocins, some with a relatively wide host range against Gram-positive bacteria and have
potential as food biopreservatives.
Leuconostoc. Spherical or lenticular cells; occur in pairs or chains; nonmotile; facultative anaerobes; heterolactic fermentators; mesophiles, but some species and strains can grow at or
below 3°C. Some are used in food fermentation. Psychrotrophic strains are associated with
spoilage (gas formation) of vacuum-packaged refrigerated foods. Found in plants, meat, and
milk. Species: Leuconostoc mesenteroides subsp. mesenteroides, Leu. lactis, Leu. carnosum; Leu.
mesenteroides subsp. dextranicum produces dextran while growing in sucrose. Several strains
produce bacteriocins, some with a wide spectrum against Gram-positive bacteria, and these
have potential as food biopreservatives.
Micrococcus. Spherical cells (0.2–2 μm); occur in pairs, tetrads, or clusters; aerobes; nonmotile;
some species produce yellow colonies; mesophiles, resistant to low heat. Found in mammalian skin. Can cause spoilage. Species: Micrococcus luteus.