14 ◾ Fundamental Food Microbiology
or a mixture of both (e.g., Pediococcus acidilactici LB923; Listeria monocytogenes ATCC 19116). At
the family level, bacterial names are used as plural adjectives in feminine gender and agree with
the suffix “aceae” (e.g., Enterobacteriaceae). The species and strains in a genus can be represented
collectively, either using “spp.” after genus (e.g., Lactobacillus spp.) or plural forms of the genus
(e.g., lactobacilli for Lactobacillus; lactococci for Lactococcus; leuconostocs for Leuconostoc, or salmonellae for Salmonella).
The scientific names of bacteria are given according to the specifications of the International
Code of Nomenclature of Bacteria. The International Committee on Systematic Bacteriology of the
International Union of Microbiological Association examines the validity of each name and then publishes the approved lists of bacterial names from time to time. A new name (species or genus) must be
published in the International Journal of Systematic Bacteriology before it is judged for inclusion in the
approved list. Any change in name (genus or species) has to be approved by this committee.
When writing the name of the same species more than once in an article, it is customary to use
both genus and specific epithet the first time and abbreviate the genus name subsequently. In the
Bergey’s Manual of Systematic Bacteriology, only the first letter is used (e.g., Listeria monocytogenes
and then L. monocytogenes). The same system is used in most publications in the United States.
However, it creates confusion when one article has several species with the same first letter in
the genus (e.g., Lactobacillus lactis, Leuconostoc lactis, and Lactococcus lactis as L. lactis). In some
European journals, more than one letter is used, but there is no definite system (e.g., Lact. lactis,
Lc. lactis, Leu. lactis, Lb. lactis, List. monocytogenes). In this book, to reduce confusion among readers, many of whom might not be familiar with the current rapid changes in bacterial nomenclature, a three-letter system is used (e.g., Lis. monocytogenes, Leu. lactis; Shi. dysenterie for Shigella;
Sta. aureus for Staphylococcus). In rare cases, a slight modification is used (e.g., Lactococcus lactis
and Lactobacillus lactis are written as Lac. lactis and Lab. lactis, respectively, for the two genera).
The nomenclature system for Salmonella has been modified (Chapter 26).
The viruses, as indicated previously, have not been given specific taxonomic names as given
for bacteria. They are often identified with alphabetic or numeric designations or a combination
of both (e.g., T4 or T1 bacteriophages), the type of disease they produce (e.g., hepatitis A, causing liver disease), or by other methods, for example, Norwalk-like viruses (now called norovirus),
causing a type of foodborne gastroenteritis in humans, originally isolated from the town called
Norwalk in Ohio (United States).
Morphology and Structure of Microorganisms in Foods
Yeasts and Molds
Both yeasts and molds are eukaryotic, but yeasts are unicellular, whereas molds are multicellular. 5,6 Eukaryotic cells are generally much larger (20–100 μm) than prokaryotic cells (1–10 μm).
Eukaryotic cells have rigid cell walls and thin plasma membranes. The cell wall does not have
peptidoglycan, is rigid, and is composed of carbohydrates. The plasma membrane contains sterol.
The cytoplasm is mobile (streaming) and contains organelles (mitochondria, vacuoles) that are
membrane bound. Ribosomes are 80S type and attached to the endoplasmic reticulum. The DNA
is linear (chromosomes), contains histones, and is enclosed in a nuclear membrane. Cell division is
by mitosis (i.e., asexual reproduction); sexual reproduction, when it occurs, is by meiosis.
Molds are nonmotile, filamentous, and branched (Figure 2.2). The cell wall is composed of cellulose, chitin, or both. A mold (thallus) is composed of large numbers of filaments called hyphae.
or a mixture of both (e.g., Pediococcus acidilactici LB923; Listeria monocytogenes ATCC 19116). At
the family level, bacterial names are used as plural adjectives in feminine gender and agree with
the suffix “aceae” (e.g., Enterobacteriaceae). The species and strains in a genus can be represented
collectively, either using “spp.” after genus (e.g., Lactobacillus spp.) or plural forms of the genus
(e.g., lactobacilli for Lactobacillus; lactococci for Lactococcus; leuconostocs for Leuconostoc, or salmonellae for Salmonella).
The scientific names of bacteria are given according to the specifications of the International
Code of Nomenclature of Bacteria. The International Committee on Systematic Bacteriology of the
International Union of Microbiological Association examines the validity of each name and then publishes the approved lists of bacterial names from time to time. A new name (species or genus) must be
published in the International Journal of Systematic Bacteriology before it is judged for inclusion in the
approved list. Any change in name (genus or species) has to be approved by this committee.
When writing the name of the same species more than once in an article, it is customary to use
both genus and specific epithet the first time and abbreviate the genus name subsequently. In the
Bergey’s Manual of Systematic Bacteriology, only the first letter is used (e.g., Listeria monocytogenes
and then L. monocytogenes). The same system is used in most publications in the United States.
However, it creates confusion when one article has several species with the same first letter in
the genus (e.g., Lactobacillus lactis, Leuconostoc lactis, and Lactococcus lactis as L. lactis). In some
European journals, more than one letter is used, but there is no definite system (e.g., Lact. lactis,
Lc. lactis, Leu. lactis, Lb. lactis, List. monocytogenes). In this book, to reduce confusion among readers, many of whom might not be familiar with the current rapid changes in bacterial nomenclature, a three-letter system is used (e.g., Lis. monocytogenes, Leu. lactis; Shi. dysenterie for Shigella;
Sta. aureus for Staphylococcus). In rare cases, a slight modification is used (e.g., Lactococcus lactis
and Lactobacillus lactis are written as Lac. lactis and Lab. lactis, respectively, for the two genera).
The nomenclature system for Salmonella has been modified (Chapter 26).
The viruses, as indicated previously, have not been given specific taxonomic names as given
for bacteria. They are often identified with alphabetic or numeric designations or a combination
of both (e.g., T4 or T1 bacteriophages), the type of disease they produce (e.g., hepatitis A, causing liver disease), or by other methods, for example, Norwalk-like viruses (now called norovirus),
causing a type of foodborne gastroenteritis in humans, originally isolated from the town called
Norwalk in Ohio (United States).
Morphology and Structure of Microorganisms in Foods
Yeasts and Molds
Both yeasts and molds are eukaryotic, but yeasts are unicellular, whereas molds are multicellular. 5,6 Eukaryotic cells are generally much larger (20–100 μm) than prokaryotic cells (1–10 μm).
Eukaryotic cells have rigid cell walls and thin plasma membranes. The cell wall does not have
peptidoglycan, is rigid, and is composed of carbohydrates. The plasma membrane contains sterol.
The cytoplasm is mobile (streaming) and contains organelles (mitochondria, vacuoles) that are
membrane bound. Ribosomes are 80S type and attached to the endoplasmic reticulum. The DNA
is linear (chromosomes), contains histones, and is enclosed in a nuclear membrane. Cell division is
by mitosis (i.e., asexual reproduction); sexual reproduction, when it occurs, is by meiosis.
Molds are nonmotile, filamentous, and branched (Figure 2.2). The cell wall is composed of cellulose, chitin, or both. A mold (thallus) is composed of large numbers of filaments called hyphae.