20
Modern Food Microbiology
for growth and would not be expected to persist in soils. The bacterial biota of seawater is essentially
Gram-negative, and Gram-positive bacteria exist there essentially only as transients. Contaminated
water has been implicated in Cyclospora contamination of fresh raspberries.
Plants and Plant Products. It may be assumed that many or most soil and water organisms contaminate plants. However, only a relatively small number find the plant environment suitable to their
overall well-being. Those that persist on plant products do so by virtue of a capacity to adhere to plant
surfaces so that they are not easily washed away and because they are able to obtain their nutritional
requirements. Notable among these are the lactic acid bacteria and some yeasts. Among others that are
commonly associated with plants are bacterial plant pathogens in the genera Corynebacterium, Curtobacterium, Pectobacterium, Pseudomonas, and Xanthomonas; and fungal pathogens among several
genera of molds.
Food Utensils. When vegetables are harvested in containers and utensils, one would expect to find
some or all of the surface organisms on the products to contaminate contact surfaces. As more and more
vegetables are placed in the same containers, a normalization of the microbiota would be expected to
occur. In a similar way, the cutting block in a meat market along with cutting knives and grinders are
contaminated from initial samples, and this process leads to a buildup of organisms, thus ensuring a
fairly constant level of contamination of meat-borne organisms.
Gastrointestinal Tract. This biota becomes a water source when polluted water is used to wash
raw food products. The intestinal biota consists of many organisms that do not persist as long in
waters as do others, and notable among these are pathogens such as salmonellae. Any or all of the
Enterobacteriaceae may be expected in fecal wastes, along with intestinal pathogens, including the
five protozoal species already listed.
Food Handlers. The microbiota on the hands and outer garments of handlers generally reflect the
environment and habits of individuals, and the organisms in question may be those from soil, water,
dust, and other environmental sources. Additional important sources are those that are common in
nasal cavities, the mouth, and on the skin, and those from the gastrointestinal tract that may enter
foods through poor personal hygiene practices.
Animal Feeds. This is a source of salmonellae to poultry and other farm animals. In the case of
some silage, it is a known source of Listeria monocytogenes to dairy and meat animals. The organisms
in dry animal feed are spread throughout the animal environment and may be expected to occur on
animal hides.
Animal Hides. In the case of milk cows, the types of organisms found in raw milk can be a reflection
of the biota of the udder when proper procedures are not followed in milking and of the general
environment of such animals. From both the udder and the hide, organisms can contaminate the
general environment, milk containers, and the hands of handlers.
Air and Dust. Although most of the organisms listed in Table 2–2 may at times be found in air
and dust in a food-processing operation, the ones that can persist include most of the Gram-positive
organisms listed. Among fungi, a number of molds may be expected to occur in air and dust, along
with some yeasts. In general, the types of organisms in air and dust would be those that are constantly
reseeded to the environment. Air ducts are not unimportant sources.
SYNOPSIS OF COMMON FOODBORNE BACTERIA
These synopses are provided to give the reader glimpses of bacterial groups that are discussed
throughout the textbook. They are not meant to be used for culture identifications. For the latter, one or
Modern Food Microbiology
for growth and would not be expected to persist in soils. The bacterial biota of seawater is essentially
Gram-negative, and Gram-positive bacteria exist there essentially only as transients. Contaminated
water has been implicated in Cyclospora contamination of fresh raspberries.
Plants and Plant Products. It may be assumed that many or most soil and water organisms contaminate plants. However, only a relatively small number find the plant environment suitable to their
overall well-being. Those that persist on plant products do so by virtue of a capacity to adhere to plant
surfaces so that they are not easily washed away and because they are able to obtain their nutritional
requirements. Notable among these are the lactic acid bacteria and some yeasts. Among others that are
commonly associated with plants are bacterial plant pathogens in the genera Corynebacterium, Curtobacterium, Pectobacterium, Pseudomonas, and Xanthomonas; and fungal pathogens among several
genera of molds.
Food Utensils. When vegetables are harvested in containers and utensils, one would expect to find
some or all of the surface organisms on the products to contaminate contact surfaces. As more and more
vegetables are placed in the same containers, a normalization of the microbiota would be expected to
occur. In a similar way, the cutting block in a meat market along with cutting knives and grinders are
contaminated from initial samples, and this process leads to a buildup of organisms, thus ensuring a
fairly constant level of contamination of meat-borne organisms.
Gastrointestinal Tract. This biota becomes a water source when polluted water is used to wash
raw food products. The intestinal biota consists of many organisms that do not persist as long in
waters as do others, and notable among these are pathogens such as salmonellae. Any or all of the
Enterobacteriaceae may be expected in fecal wastes, along with intestinal pathogens, including the
five protozoal species already listed.
Food Handlers. The microbiota on the hands and outer garments of handlers generally reflect the
environment and habits of individuals, and the organisms in question may be those from soil, water,
dust, and other environmental sources. Additional important sources are those that are common in
nasal cavities, the mouth, and on the skin, and those from the gastrointestinal tract that may enter
foods through poor personal hygiene practices.
Animal Feeds. This is a source of salmonellae to poultry and other farm animals. In the case of
some silage, it is a known source of Listeria monocytogenes to dairy and meat animals. The organisms
in dry animal feed are spread throughout the animal environment and may be expected to occur on
animal hides.
Animal Hides. In the case of milk cows, the types of organisms found in raw milk can be a reflection
of the biota of the udder when proper procedures are not followed in milking and of the general
environment of such animals. From both the udder and the hide, organisms can contaminate the
general environment, milk containers, and the hands of handlers.
Air and Dust. Although most of the organisms listed in Table 2–2 may at times be found in air
and dust in a food-processing operation, the ones that can persist include most of the Gram-positive
organisms listed. Among fungi, a number of molds may be expected to occur in air and dust, along
with some yeasts. In general, the types of organisms in air and dust would be those that are constantly
reseeded to the environment. Air ducts are not unimportant sources.
SYNOPSIS OF COMMON FOODBORNE BACTERIA
These synopses are provided to give the reader glimpses of bacterial groups that are discussed
throughout the textbook. They are not meant to be used for culture identifications. For the latter, one or