Fundamental Food Microbiology, Third Edition - Fuad Fathir

28 FUNDAMENTAL FOOD MICROBIOLOGY
5. Gram-Positive, Endospore-Forming Rods
Bacillus. Rod-shaped, straight cells; vary widely in size (small, medium, or large;
0.5–1 ¥ 2–10 mm) 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.
Sporolactobacillus. Slender, medium-sized rods (1 ¥ 4 mm); 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.
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.
6. Gram-Negative, Endospore-Forming Rods
Desulfotomaculum. One species important in food is Delsufatomaculum nigrificans.
The medium-sized cells are rod shaped, motile, thermophilic, strictly anaerobes,
and produce H 2S. Endospores are oval and resistant to heat. Found in soil. Cause
spoilage of canned food.
7. Gram-Positive, Nonsporulating Regular Rods
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.
Carnobacterium. Similar in many characteristics to lactobacilli cells; found in meat
and fish; facultative anaerobes; heterofermentative; nonmotile; can grow in foods,