Taxonomy, Role, and Significance of Microorganisms in Foods
27
to the leuconostocs, and with the exception of W. paramesenteroides and W. hellenica, they produce
dl-lactate from glucose. All produce gas from carbohydrates. W. hellenica is a new species associated
with fermented Greek sausages.
9 The former Leuconostoc paramesenteroides is now W. paramesenteroides, and the following five species were formerly classified as Lactobacillus spp.: W. confusa, W. halotolerans, W. kandleri, W. minor, and W. viridescens. The G + C content of DNA is
37–47 mol%.
Yersinia (yer • si’ni • a). This genus includes the agent of human plague, Y. pestis, and at least one
species that causes foodborne gastroenteritis, Y. enterocolitica. All foodborne species are discussed in
Chapter 28. The mol% G + C content of DNA is 45.8–46.8. The sorbose-positive biogroup 3A strains
have been elevated to species status as Y. mollaretti and the sorbose-negative strains as Y. bercovieri.
49
SYNOPSIS OF COMMON GENERA OF FOODBORNE MOLDS
Molds are filamentous fungi that grow in the form of a tangled mass that spreads rapidly and may
cover several inches of area in 2 to 3 days. The total of the mass or any large portion of it is referred to
as mycelium. Mycelium is composed of branches or filaments referred to as hyphae. Those of greatest
importance in foods multiply by ascospores, zygospores, or conidia. The ascospores of some genera
are notable for their extreme degrees of heat resistance. One group forms pycnidia or acervuli (small,
flask-shaped, fruiting bodies lined with conidiophores). Arthrospores result from the fragmentation of
hyphae in some groups.
There were no radical changes in the systematics of foodborne fungi during the 1980s. The most
notable changes involve the discovery of the sexual or perfect states of some well-known genera
and species. In this regard, the ascomycete state is believed by mycologists to be the more important
reproductive state of a fungus, and this state is referred to as the teleomorph. The species name given to
a teleomorph takes precedence over that for the anamorph, the imperfect or conidial state. Holomorph
indicates that both states are known, but the teleomorph name is used.
The taxonomic positions of the genera described are summarized below. (Consult references 3, 4,
and 37 for identifications; see reference 25 for the types that exist in meats.)
Division: Zygomycota
Class: Zygomycetes (nonseptate mycelium, reproduction by sporangiospores, rapid growth)
Order: Mucorales
Family: Mucoraceae
Genus: Mucor
Rhizopus
Thamnidium
Division: Ascomycota
Class: Plectomycetes (septate mycelium, ascospores produced in asci usually number 8)
Order: Eurotiales
Family: Trichocomaceae
Genus: Byssochlamys
Emericella
Eupenicillium
Eurotium
27
to the leuconostocs, and with the exception of W. paramesenteroides and W. hellenica, they produce
dl-lactate from glucose. All produce gas from carbohydrates. W. hellenica is a new species associated
with fermented Greek sausages.
9 The former Leuconostoc paramesenteroides is now W. paramesenteroides, and the following five species were formerly classified as Lactobacillus spp.: W. confusa, W. halotolerans, W. kandleri, W. minor, and W. viridescens. The G + C content of DNA is
37–47 mol%.
Yersinia (yer • si’ni • a). This genus includes the agent of human plague, Y. pestis, and at least one
species that causes foodborne gastroenteritis, Y. enterocolitica. All foodborne species are discussed in
Chapter 28. The mol% G + C content of DNA is 45.8–46.8. The sorbose-positive biogroup 3A strains
have been elevated to species status as Y. mollaretti and the sorbose-negative strains as Y. bercovieri.
49
SYNOPSIS OF COMMON GENERA OF FOODBORNE MOLDS
Molds are filamentous fungi that grow in the form of a tangled mass that spreads rapidly and may
cover several inches of area in 2 to 3 days. The total of the mass or any large portion of it is referred to
as mycelium. Mycelium is composed of branches or filaments referred to as hyphae. Those of greatest
importance in foods multiply by ascospores, zygospores, or conidia. The ascospores of some genera
are notable for their extreme degrees of heat resistance. One group forms pycnidia or acervuli (small,
flask-shaped, fruiting bodies lined with conidiophores). Arthrospores result from the fragmentation of
hyphae in some groups.
There were no radical changes in the systematics of foodborne fungi during the 1980s. The most
notable changes involve the discovery of the sexual or perfect states of some well-known genera
and species. In this regard, the ascomycete state is believed by mycologists to be the more important
reproductive state of a fungus, and this state is referred to as the teleomorph. The species name given to
a teleomorph takes precedence over that for the anamorph, the imperfect or conidial state. Holomorph
indicates that both states are known, but the teleomorph name is used.
The taxonomic positions of the genera described are summarized below. (Consult references 3, 4,
and 37 for identifications; see reference 25 for the types that exist in meats.)
Division: Zygomycota
Class: Zygomycetes (nonseptate mycelium, reproduction by sporangiospores, rapid growth)
Order: Mucorales
Family: Mucoraceae
Genus: Mucor
Rhizopus
Thamnidium
Division: Ascomycota
Class: Plectomycetes (septate mycelium, ascospores produced in asci usually number 8)
Order: Eurotiales
Family: Trichocomaceae
Genus: Byssochlamys
Emericella
Eupenicillium
Eurotium