34 ◾ Fundamental Food Microbiology
Predominant Microorganisms in Different Sources
Plants (Fruits and Vegetables)
The inside tissue of foods from plant sources are essentially sterile, except for a few porous vegetables (e.g., radishes and onions) and leafy vegetables (e.g., cabbage and Brussels sprouts). 1–3 Some
plants produce natural antimicrobial metabolites that can limit the presence of microorganisms.
Fruits and vegetables harbor microorganisms on the surface; their type and level vary with soil
condition, type of fertilizers and water used, and air quality. Molds, yeasts, lactic acid bacteria, and
bacteria from genera Pseudomonas, Alcaligenes, Micrococcus, Erwinia, Bacillus, Clostridium, and
Enterobacter can be expected from this source. Pathogens, especially of enteric types (Salmonella,
Escherichia coli, Campylobacter, Shigella, Cyclospora, Giardia), can be present if the soil is contaminated with untreated sewage. Diseases of the plants, damage of the surface (before, during, and
after harvest), long delay between harvesting and washing, and unfavorable storage and transport
conditions after harvesting and before processing can greatly increase microbial numbers as well
as predominant types. Improper storage conditions following processing can also increase their
numbers.
Proper methods used during growing (such as use of treated sewage or other types of fertilizers), damage reduction during harvesting, quick washing with good-quality water to remove
soil and dirt, and storage at low temperatures before and after processing can be used to reduce
microbial load in foods of plant origin.
Animals, Birds, Fish, and Shellfish
Food animals and birds normally carry many types of indigenous microorganisms in the digestive, respiratory, and urogenital tracts; the teat canal in the udder; and in the skin, hooves, hair,
and feathers. 4–6 Their numbers, depending on the specific organ, can be very high (large intestinal contents can have as high as 10 12 microbes/g). Many, as carriers, can harbor pathogens,
such as Salmonella serovars, pathogenic Escherichia coli, Campylobacter jejuni, Yersinia enterocolitica, and Listeria monocytogenes, without showing symptoms. Laying birds have been suspected
Meat animals
Poultry and egg
Dairy cows
Seafoods
Humans
Fruits and
vegetables
Contact with
animals
Herbs and
spices
Figure 3.1 Diagram showing various sources for foodborne pathogens. ↔, indicates person-toperson transmission.
Predominant Microorganisms in Different Sources
Plants (Fruits and Vegetables)
The inside tissue of foods from plant sources are essentially sterile, except for a few porous vegetables (e.g., radishes and onions) and leafy vegetables (e.g., cabbage and Brussels sprouts). 1–3 Some
plants produce natural antimicrobial metabolites that can limit the presence of microorganisms.
Fruits and vegetables harbor microorganisms on the surface; their type and level vary with soil
condition, type of fertilizers and water used, and air quality. Molds, yeasts, lactic acid bacteria, and
bacteria from genera Pseudomonas, Alcaligenes, Micrococcus, Erwinia, Bacillus, Clostridium, and
Enterobacter can be expected from this source. Pathogens, especially of enteric types (Salmonella,
Escherichia coli, Campylobacter, Shigella, Cyclospora, Giardia), can be present if the soil is contaminated with untreated sewage. Diseases of the plants, damage of the surface (before, during, and
after harvest), long delay between harvesting and washing, and unfavorable storage and transport
conditions after harvesting and before processing can greatly increase microbial numbers as well
as predominant types. Improper storage conditions following processing can also increase their
numbers.
Proper methods used during growing (such as use of treated sewage or other types of fertilizers), damage reduction during harvesting, quick washing with good-quality water to remove
soil and dirt, and storage at low temperatures before and after processing can be used to reduce
microbial load in foods of plant origin.
Animals, Birds, Fish, and Shellfish
Food animals and birds normally carry many types of indigenous microorganisms in the digestive, respiratory, and urogenital tracts; the teat canal in the udder; and in the skin, hooves, hair,
and feathers. 4–6 Their numbers, depending on the specific organ, can be very high (large intestinal contents can have as high as 10 12 microbes/g). Many, as carriers, can harbor pathogens,
such as Salmonella serovars, pathogenic Escherichia coli, Campylobacter jejuni, Yersinia enterocolitica, and Listeria monocytogenes, without showing symptoms. Laying birds have been suspected
Meat animals
Poultry and egg
Dairy cows
Seafoods
Humans
Fruits and
vegetables
Contact with
animals
Herbs and
spices
Figure 3.1 Diagram showing various sources for foodborne pathogens. ↔, indicates person-toperson transmission.