24
Modern Food Microbiology
long chains. Although those in foods are typically microaerophilic, many true anaerobic strains exist,
especially in the colon and the rumen. They typically occur on most, if not all, vegetables, along with
some of the other lactic acid bacteria. Their occurrence in dairy products is common. One species, L.
suebicus, was recovered from apple and pear mashes; it grows at pH 2.8 and in 12–16% ethanol.
28
Many fermented products are produced, and these are discussed in Chapter 7. Those that are common
on refrigerator-stored, vacuum-packaged meats are discussed in Chapters 5 and 14.
Lactococcus (lac • to • coc’cus). The nonmotile Lancefield serologic group N cocci once classified
in the genus Streptococcus have been elevated to generic status. They are Gram-positive, nonmotile,
and catalase-negative, spherical, or ovoid cells, that occur singly, in pairs, or as chains. They grow at
10
◦ C but not at 45
◦ C, and most strains react with group N antisera. l-Lactic acid is the predominant
end-product of fermentation.
Leuconostoc (leu • co • nos’toc; colorless nostoc). Along with the lactobacilli, this is another of the
genera of lactic acid bacteria. They are Gram-positive, catalase-negative cocci that are heterofermentative. The genus has been reduced in number of species (see Weissella below). The former L. oenos
has been transferred to a new genus, Oenococcus as O. oeni,
16 and the former L. paramesenteroides
has been transferred to the new genus Weissella. These cocci are typically found in association with
the lactobacilli.
Listeria (lis • te’ri • a). This genus of six species of Gram-positive, nonsporing rods is closely related to
Brochothrix. The six species show 80% similarity by numerical taxonomic studies; they have identical
cell walls, fatty acid, and cytochrome composition. They are more fully described and discussed in
Chapter 25.
Micrococcus (mi • cro • coc’cus). These Gram-positive and catalase-positive cocci are inhabitants of
mammalian skin and can grow in the presence of high levels of NaCl. This genus has been reduced
by the creation of the following five new genera: Dermacoccus, Kocuria, Kytococcus, Nesterenkonia,
and Stomatococcus. At the present time, M. luteus and M. lylae are the only two micrococcal species.
Moraxella (mo • rax • el’la). These short Gram-negative rods are sometimes classified as Acinetobacter.
They differ from the latter in being sensitive to penicillin and oxidase positive and having a mol%
G + C content of DNA of 40–46. The genus Psychrobacter includes some that were once placed in
this genus. Their metabolism is oxidative, and they do not form acid from glucose.
Paenibacillus (pae • ba • cil’lus; almost a bacillus). This newly established genus comprises organisms
formerly in the genera Bacillus and Clostridium, and it includes the following species: P. alvei,
P. amylolyticus, P. azotofixans, P. circulans, P. durum, P. larvae, P. macerans, P. macquariensis,
P. pubuli, P. pulvifaciens, and P. validus.
2,8 Recently, two new species were added (P. lautus and P.
peoriae
22 ). The paenibacilli are notable for their degradation of a number of macromolecules, their
production of antibacterial and antifungal agents, and the capacity of some to fix N 2 in association
with plants. A newly-named species was isolated from raw and UHT-treated milk.
38
Pandoraea (Pan • do • rae’a). Although first isolated from sputa of cystic fibrosis patients,
7 these
organisms are related to some of the pseudomonads. Although not demonstrated to be common in
foods, one species, P. norimbergenesis, has been isolated from powdered milk.
35
Modern Food Microbiology
long chains. Although those in foods are typically microaerophilic, many true anaerobic strains exist,
especially in the colon and the rumen. They typically occur on most, if not all, vegetables, along with
some of the other lactic acid bacteria. Their occurrence in dairy products is common. One species, L.
suebicus, was recovered from apple and pear mashes; it grows at pH 2.8 and in 12–16% ethanol.
28
Many fermented products are produced, and these are discussed in Chapter 7. Those that are common
on refrigerator-stored, vacuum-packaged meats are discussed in Chapters 5 and 14.
Lactococcus (lac • to • coc’cus). The nonmotile Lancefield serologic group N cocci once classified
in the genus Streptococcus have been elevated to generic status. They are Gram-positive, nonmotile,
and catalase-negative, spherical, or ovoid cells, that occur singly, in pairs, or as chains. They grow at
10
◦ C but not at 45
◦ C, and most strains react with group N antisera. l-Lactic acid is the predominant
end-product of fermentation.
Leuconostoc (leu • co • nos’toc; colorless nostoc). Along with the lactobacilli, this is another of the
genera of lactic acid bacteria. They are Gram-positive, catalase-negative cocci that are heterofermentative. The genus has been reduced in number of species (see Weissella below). The former L. oenos
has been transferred to a new genus, Oenococcus as O. oeni,
16 and the former L. paramesenteroides
has been transferred to the new genus Weissella. These cocci are typically found in association with
the lactobacilli.
Listeria (lis • te’ri • a). This genus of six species of Gram-positive, nonsporing rods is closely related to
Brochothrix. The six species show 80% similarity by numerical taxonomic studies; they have identical
cell walls, fatty acid, and cytochrome composition. They are more fully described and discussed in
Chapter 25.
Micrococcus (mi • cro • coc’cus). These Gram-positive and catalase-positive cocci are inhabitants of
mammalian skin and can grow in the presence of high levels of NaCl. This genus has been reduced
by the creation of the following five new genera: Dermacoccus, Kocuria, Kytococcus, Nesterenkonia,
and Stomatococcus. At the present time, M. luteus and M. lylae are the only two micrococcal species.
Moraxella (mo • rax • el’la). These short Gram-negative rods are sometimes classified as Acinetobacter.
They differ from the latter in being sensitive to penicillin and oxidase positive and having a mol%
G + C content of DNA of 40–46. The genus Psychrobacter includes some that were once placed in
this genus. Their metabolism is oxidative, and they do not form acid from glucose.
Paenibacillus (pae • ba • cil’lus; almost a bacillus). This newly established genus comprises organisms
formerly in the genera Bacillus and Clostridium, and it includes the following species: P. alvei,
P. amylolyticus, P. azotofixans, P. circulans, P. durum, P. larvae, P. macerans, P. macquariensis,
P. pubuli, P. pulvifaciens, and P. validus.
2,8 Recently, two new species were added (P. lautus and P.
peoriae
22 ). The paenibacilli are notable for their degradation of a number of macromolecules, their
production of antibacterial and antifungal agents, and the capacity of some to fix N 2 in association
with plants. A newly-named species was isolated from raw and UHT-treated milk.
38
Pandoraea (Pan • do • rae’a). Although first isolated from sputa of cystic fibrosis patients,
7 these
organisms are related to some of the pseudomonads. Although not demonstrated to be common in
foods, one species, P. norimbergenesis, has been isolated from powdered milk.
35