Taxonomy, Role, and Significance of Microorganisms in Foods
25
Pantoea (pan • toe’a). This genus consists of Gram-negative, noncapsulated, nonsporing straight
rods, most of which are motile by peritrichous flagella. They are widely distributed and are found
on plants and in seeds, in soil, water, and human specimens. Some are plant pathogens. The four
recognized species were once classified as enterobacters or erwinias. P. agglomerans includes the
former Enterobacter agglomerans, Erwinia herbicola, and E. milletiae; P. ananas includes the former
Erwinia ananas and E. uredovora; P. stewartii was once E. stewartii; and P. dispersa is an original
species.
18 The G + C content of DNA ranges from 49.7 to 60.6 mol%.
33
Pediococcus (pe • di • o • coc’cus; coccus growing in one plane). These homofermentative cocci
are lactic acid bacteria that exist in pairs and tetrads resulting from cell division in two planes. P.
acidilactici, a common starter species, caused septicemia in a 53-year-old male.
19 Their mol% G + C
content of DNA is 34–44; they are further discussed in Chapter 7. The once P. halophilus is now in
the genus Tetragenococcus as T. halophilus. It can grow in 18% NaCl.
Proteus (pro’te • us). These enteric Gram-negative rods are aerobes that often display pleomorphism,
hence the generic name. All are motile and typically produce swarming growth on the surface of moist
agar plates. They are typical of enteric bacteria in being present in the intestinal tract of humans and
animals. They may be isolated from a variety of vegetable and meat products, especially those that
undergo spoilage at temperatures in the mesophilic range.
Pseudomonas (pseu • do’mo • nas; false monad). These are typical soil and water bacteria and they
are widely distributed among fresh foods, especially vegetables, meats, poultry, and seafood products. Although once the largest genus of foodborne bacteria, the genus has been delimited by the
transfer of many former species to at least 13 new genera: Acidovorax, Aminobacter, Brevundimonas,
Burkholderia, Comamonas, Delftia, Devosia, Herbaspirillium, Hydrogenophaga, Marinobacter, Ralstonia, Sphingomonas, Telluria, and Wautersia. P. fluorescens and P. aeruginosa remain in the original
genus (see reference 24).
Psychrobacter (psy • chro’ • bac • ter). This genus was created primarily to accommodate some of the
nonmotile Gram-negative rods that were once classified in the genera Acinetobacter and Moraxella.
They are plump coccobacilli that often occur in pairs. Also, they are aerobic, nonmotile, and catalase
and oxidase positive, and generally do not ferment glucose. Growth occurs in 6.5% NaCl and at
1
◦ C, but generally not at 35
◦ C or 37
◦ C. They hydrolyze Tween 80, and most are egg-yolk positive
(lecithinase). They are sensitive to penicillin and utilize γ -aminovalerate, whereas the acinetobacters
do not. They are distinguished from the acinetobacters by being oxidase positive and aminovalerate
users and from nonmotile pseudomonads by their inability to utilize glycerol or fructose. Because
they closely resemble the moraxellae, they have been placed in the family Neisseriaceae. The genus
contains some of the former achromobacters and moraxellae, as noted. They are common on meats,
poultry, and fish, and in water.
26,39
Salmonella (sal • mon • el’la). All members of this genus of Gram-negative enteric bacteria are considered to be human pathogens. It should be noted that the salmonellae have been placed in two species
with those that affect humans placed in the species Salmonella enterica. The serotypes (serovars) of
more than 2,400 are listed as follows: Salmonella enterica serotype Newport, or Salmonella Newport
(note that the serotype is not italicized). (See Chapter 26 for a more detailed explanation.) The mol%
G + C content of DNA is 50–53.
25
Pantoea (pan • toe’a). This genus consists of Gram-negative, noncapsulated, nonsporing straight
rods, most of which are motile by peritrichous flagella. They are widely distributed and are found
on plants and in seeds, in soil, water, and human specimens. Some are plant pathogens. The four
recognized species were once classified as enterobacters or erwinias. P. agglomerans includes the
former Enterobacter agglomerans, Erwinia herbicola, and E. milletiae; P. ananas includes the former
Erwinia ananas and E. uredovora; P. stewartii was once E. stewartii; and P. dispersa is an original
species.
18 The G + C content of DNA ranges from 49.7 to 60.6 mol%.
33
Pediococcus (pe • di • o • coc’cus; coccus growing in one plane). These homofermentative cocci
are lactic acid bacteria that exist in pairs and tetrads resulting from cell division in two planes. P.
acidilactici, a common starter species, caused septicemia in a 53-year-old male.
19 Their mol% G + C
content of DNA is 34–44; they are further discussed in Chapter 7. The once P. halophilus is now in
the genus Tetragenococcus as T. halophilus. It can grow in 18% NaCl.
Proteus (pro’te • us). These enteric Gram-negative rods are aerobes that often display pleomorphism,
hence the generic name. All are motile and typically produce swarming growth on the surface of moist
agar plates. They are typical of enteric bacteria in being present in the intestinal tract of humans and
animals. They may be isolated from a variety of vegetable and meat products, especially those that
undergo spoilage at temperatures in the mesophilic range.
Pseudomonas (pseu • do’mo • nas; false monad). These are typical soil and water bacteria and they
are widely distributed among fresh foods, especially vegetables, meats, poultry, and seafood products. Although once the largest genus of foodborne bacteria, the genus has been delimited by the
transfer of many former species to at least 13 new genera: Acidovorax, Aminobacter, Brevundimonas,
Burkholderia, Comamonas, Delftia, Devosia, Herbaspirillium, Hydrogenophaga, Marinobacter, Ralstonia, Sphingomonas, Telluria, and Wautersia. P. fluorescens and P. aeruginosa remain in the original
genus (see reference 24).
Psychrobacter (psy • chro’ • bac • ter). This genus was created primarily to accommodate some of the
nonmotile Gram-negative rods that were once classified in the genera Acinetobacter and Moraxella.
They are plump coccobacilli that often occur in pairs. Also, they are aerobic, nonmotile, and catalase
and oxidase positive, and generally do not ferment glucose. Growth occurs in 6.5% NaCl and at
1
◦ C, but generally not at 35
◦ C or 37
◦ C. They hydrolyze Tween 80, and most are egg-yolk positive
(lecithinase). They are sensitive to penicillin and utilize γ -aminovalerate, whereas the acinetobacters
do not. They are distinguished from the acinetobacters by being oxidase positive and aminovalerate
users and from nonmotile pseudomonads by their inability to utilize glycerol or fructose. Because
they closely resemble the moraxellae, they have been placed in the family Neisseriaceae. The genus
contains some of the former achromobacters and moraxellae, as noted. They are common on meats,
poultry, and fish, and in water.
26,39
Salmonella (sal • mon • el’la). All members of this genus of Gram-negative enteric bacteria are considered to be human pathogens. It should be noted that the salmonellae have been placed in two species
with those that affect humans placed in the species Salmonella enterica. The serotypes (serovars) of
more than 2,400 are listed as follows: Salmonella enterica serotype Newport, or Salmonella Newport
(note that the serotype is not italicized). (See Chapter 26 for a more detailed explanation.) The mol%
G + C content of DNA is 50–53.