536 ◾ Fundamental Food Microbiology
with unpasteurized milk, ice cream, butter, etc.), or minimally processed fruits (apple cider, strawberries, raspberries, cantaloupe, etc.) and vegetables (sprouts, lettuce, spinach, etc.). Food animals
and poultry are the most important reservoirs for many of the foodborne pathogens, including
Salmonella, Campylobacter, Listeria, or Escherichia coli O157:H7. Animal byproducts, such as feed
supplements, may transmit pathogens to other animals (e.g., Salmonella, Prion associated with
bovine spongiform encephalopathy [BSE] or mad cow disease). Application of untreated manure
onto farmland can also contaminate soil or water with the eventual contamination of fruits and
vegetables. Seafoods are another potential source of foodborne pathogens, including Vibrio species, Listeria monocytogenes, and Hepatitis A. Infectious doses of many of these pathogens are very
low (~10–1000 cells). Detection technologies, both traditional and rapid, are able to detect such
low numbers, but they are lengthy and laborious. Furthermore, ongoing concern with intentional
administration of harmful microorganisms or toxins in food or water supplies demands significant
improvement in detection technologies for a fast time to result with a high degree of accuracy.
Modern biosensor technologies are showing some promising results in pathogen detection and
principles, and application of some selected technologies are presented later in this chapter.
Methods Used
The methods used for the microbiological evaluation or detection of foods, food ingredients, and
environments are broadly grouped as quantitative and qualitative methods. 1–4 The quantitative
methods are designed to enumerate or estimate directly or indirectly the microbial load in a test
material. It should be recognized that none of the quantitative methods that are used now enumerate or estimate “total microbes,” “total bacteria,” or “total viable population” (terms used by many)
present in a food although they can be obtained for a pure culture of a microbial strain growing in
a sterile liquid or a solid medium. Rather, each method enumerates or estimates a specific group
among the total microbial population that is normally present in a food, which grows or multiplies
preferentially under the conditions or methods of testing. These include composition of an enumeration medium, temperature and time of incubation and oxygen availability during incubation,
pH, and treatments given to a sample prior to enumeration and estimation. Examples of some of
the quantitative methods used are total aerobic plate counts (TAPC) (or standard plate counts,
SPC, for dairy products), anaerobic counts, psychrotrophic counts, thermoduric counts, coliform
counts, Staphylococcus aureus counts, and yeast and mold counts.
In contrast, qualitative methods are designed to determine whether a representative amount (a
sample) of a food or a certain number of samples in a batch of a food contain a specific microbial species
among the total microbial population or not. These methods are used to detect the possible presence of
certain foodborne pathogens, especially those capable of inflicting high fatality rates among the consumers. Salmonella, Clostridium botulinum, Escherichia coli O157:H7 and other Shiga-toxin producing
Esc. coli (STEC), and Listeria monocytogenes in ready-to-eat foods are some that fall into this group.
Standard and Recommended Methods
Many methods and variations of different methods that can be used for quantitative and qualitative detection of microorganisms in foods are reported in the literature. However, it is desirable to
use methods that have been approved by the regulatory agencies. They can be either standard or
recommended methods. In the United States, for the microbiological examinations of milk and
with unpasteurized milk, ice cream, butter, etc.), or minimally processed fruits (apple cider, strawberries, raspberries, cantaloupe, etc.) and vegetables (sprouts, lettuce, spinach, etc.). Food animals
and poultry are the most important reservoirs for many of the foodborne pathogens, including
Salmonella, Campylobacter, Listeria, or Escherichia coli O157:H7. Animal byproducts, such as feed
supplements, may transmit pathogens to other animals (e.g., Salmonella, Prion associated with
bovine spongiform encephalopathy [BSE] or mad cow disease). Application of untreated manure
onto farmland can also contaminate soil or water with the eventual contamination of fruits and
vegetables. Seafoods are another potential source of foodborne pathogens, including Vibrio species, Listeria monocytogenes, and Hepatitis A. Infectious doses of many of these pathogens are very
low (~10–1000 cells). Detection technologies, both traditional and rapid, are able to detect such
low numbers, but they are lengthy and laborious. Furthermore, ongoing concern with intentional
administration of harmful microorganisms or toxins in food or water supplies demands significant
improvement in detection technologies for a fast time to result with a high degree of accuracy.
Modern biosensor technologies are showing some promising results in pathogen detection and
principles, and application of some selected technologies are presented later in this chapter.
Methods Used
The methods used for the microbiological evaluation or detection of foods, food ingredients, and
environments are broadly grouped as quantitative and qualitative methods. 1–4 The quantitative
methods are designed to enumerate or estimate directly or indirectly the microbial load in a test
material. It should be recognized that none of the quantitative methods that are used now enumerate or estimate “total microbes,” “total bacteria,” or “total viable population” (terms used by many)
present in a food although they can be obtained for a pure culture of a microbial strain growing in
a sterile liquid or a solid medium. Rather, each method enumerates or estimates a specific group
among the total microbial population that is normally present in a food, which grows or multiplies
preferentially under the conditions or methods of testing. These include composition of an enumeration medium, temperature and time of incubation and oxygen availability during incubation,
pH, and treatments given to a sample prior to enumeration and estimation. Examples of some of
the quantitative methods used are total aerobic plate counts (TAPC) (or standard plate counts,
SPC, for dairy products), anaerobic counts, psychrotrophic counts, thermoduric counts, coliform
counts, Staphylococcus aureus counts, and yeast and mold counts.
In contrast, qualitative methods are designed to determine whether a representative amount (a
sample) of a food or a certain number of samples in a batch of a food contain a specific microbial species
among the total microbial population or not. These methods are used to detect the possible presence of
certain foodborne pathogens, especially those capable of inflicting high fatality rates among the consumers. Salmonella, Clostridium botulinum, Escherichia coli O157:H7 and other Shiga-toxin producing
Esc. coli (STEC), and Listeria monocytogenes in ready-to-eat foods are some that fall into this group.
Standard and Recommended Methods
Many methods and variations of different methods that can be used for quantitative and qualitative detection of microorganisms in foods are reported in the literature. However, it is desirable to
use methods that have been approved by the regulatory agencies. They can be either standard or
recommended methods. In the United States, for the microbiological examinations of milk and