20 ◾ Fundamental Food Microbiology
their multiplication inside the host. These organisms cause typical gastroenteritis with abdominal
cramps and sometimes muscle ache, fever, and headache.
Important Viruses
Viruses are important in food for several reasons. 5,10–12
1. Some are able to cause enteric disease and, thus, if present in a food, can cause foodborne
diseases. Hepatitis A and norovirus have been implicated in foodborne outbreaks. Several
other enteric viruses, such as poliovirus, adenovirus, echo virus, rota virus, saporovirus,
hepatitis E virus, and Coxsackie virus, can cause foodborne diseases. In some countries
where the level of sanitation is not very high, they can contaminate foods and cause disease.
2. Some bacterial viruses (bacteriophages) are used to detect and identify some pathogens
(Salmonella serovars, Listeria monocytogenes, Staphylococcus aureus) on the basis of the sensitivity of the cells to a series of bacteriophages at appropriate dilutions.
3. Bacteriophages are used to transfer genetic traits in some bacterial species or strains by a
process called transduction (e.g., in Escherichia coli or Lactococcus lactis).
4. Bacteriophages as biocontrol agents as antimicrobials to control pathogens such as
Listeria monocytogenes, Esc. coli O157:H7, and Salmonella in foods or in food-production
environments.
5. Finally, some bacteriophages can be very important because they can cause fermentation
failure. Many lactic acid bacteria, used as starter cultures in food fermentation, are sensitive
to different bacteriophages. They can infect and destroy starter-culture bacteria, causing
product failure. Among the lactic acid bacteria, bacteriophages have been isolated for many
species in the genera Lactococcus, Streptococcus, Leuconostoc, and Lactobacillus; no bacteriophage of Pediococcus is yet known. Methods are being devised to genetically engineer lactic
starter cultures so that they become resistant to multiple bacteriophages (see Chapter 14).
Important Bacterial Genera
Bacterial classification is changing rapidly. 1 In Bergey’s Manual of Systematic Bacteriology, published
between 1984 and 1988, more than 420 bacterial genera are listed in 33 sections on the basis
of their differences in characteristics. Since then, many other genera have been created, such as
Lactococcus (former N-group or dairy Streptococcus) and Carnobacterium (some species previously
included in Lactobacillus). In the ninth edition of Bergey’s Manual of Determinative Bacteriology
(1993), more than 560 genera are listed in 35 groups. Of these, Table 2.1 lists 48 genera whose
species are frequently associated with spoilage, health hazards, and bioprocessing of food. Species
of other genera besides these 48 can also be found in food, but their relative significance is not well
established. Many species names in several genera are also no longer valid and thus not included
in the current Bergey’s Manual of Determinative Bacteriology. In this text, only species and genera
currently approved and listed in Bergey’s Manual are used. Brief important characteristics of these
genera and their importance in foods are described. Some descriptions are also presented in other
chapters, such as pathogens in Chapters 25–29 and beneficial bacteria (bioprocessing) in Chapters
11 and 18.
their multiplication inside the host. These organisms cause typical gastroenteritis with abdominal
cramps and sometimes muscle ache, fever, and headache.
Important Viruses
Viruses are important in food for several reasons. 5,10–12
1. Some are able to cause enteric disease and, thus, if present in a food, can cause foodborne
diseases. Hepatitis A and norovirus have been implicated in foodborne outbreaks. Several
other enteric viruses, such as poliovirus, adenovirus, echo virus, rota virus, saporovirus,
hepatitis E virus, and Coxsackie virus, can cause foodborne diseases. In some countries
where the level of sanitation is not very high, they can contaminate foods and cause disease.
2. Some bacterial viruses (bacteriophages) are used to detect and identify some pathogens
(Salmonella serovars, Listeria monocytogenes, Staphylococcus aureus) on the basis of the sensitivity of the cells to a series of bacteriophages at appropriate dilutions.
3. Bacteriophages are used to transfer genetic traits in some bacterial species or strains by a
process called transduction (e.g., in Escherichia coli or Lactococcus lactis).
4. Bacteriophages as biocontrol agents as antimicrobials to control pathogens such as
Listeria monocytogenes, Esc. coli O157:H7, and Salmonella in foods or in food-production
environments.
5. Finally, some bacteriophages can be very important because they can cause fermentation
failure. Many lactic acid bacteria, used as starter cultures in food fermentation, are sensitive
to different bacteriophages. They can infect and destroy starter-culture bacteria, causing
product failure. Among the lactic acid bacteria, bacteriophages have been isolated for many
species in the genera Lactococcus, Streptococcus, Leuconostoc, and Lactobacillus; no bacteriophage of Pediococcus is yet known. Methods are being devised to genetically engineer lactic
starter cultures so that they become resistant to multiple bacteriophages (see Chapter 14).
Important Bacterial Genera
Bacterial classification is changing rapidly. 1 In Bergey’s Manual of Systematic Bacteriology, published
between 1984 and 1988, more than 420 bacterial genera are listed in 33 sections on the basis
of their differences in characteristics. Since then, many other genera have been created, such as
Lactococcus (former N-group or dairy Streptococcus) and Carnobacterium (some species previously
included in Lactobacillus). In the ninth edition of Bergey’s Manual of Determinative Bacteriology
(1993), more than 560 genera are listed in 35 groups. Of these, Table 2.1 lists 48 genera whose
species are frequently associated with spoilage, health hazards, and bioprocessing of food. Species
of other genera besides these 48 can also be found in food, but their relative significance is not well
established. Many species names in several genera are also no longer valid and thus not included
in the current Bergey’s Manual of Determinative Bacteriology. In this text, only species and genera
currently approved and listed in Bergey’s Manual are used. Brief important characteristics of these
genera and their importance in foods are described. Some descriptions are also presented in other
chapters, such as pathogens in Chapters 25–29 and beneficial bacteria (bioprocessing) in Chapters
11 and 18.