Fundamental Food Microbiology, Third Edition - Fuad Fathir

CHARACTERISTICS OF PREDOMINANT MICROORGANISMS IN FOOD 27
4. Gram-Positive Cocci
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Micrococcus. Spherical cells (0.2 to 2 mm); 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.
Staphylococcus. Spherical cells (0.5 to 1 mm); occur singly, in pairs, or 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 mm); 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.
Enterococcus. Spheroid cells (1 mm); 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 to 1.0 mm); 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.
Pediococcus. Spherical cells (1 mm); 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 to 2 mm); 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.