Transcript Food poisoning

LECTURE PRESENTATIONS
For BROCK BIOLOGY OF MICROORGANISMS, THIRTEENTH EDITION
Michael T. Madigan, John M. Martinko, David A. Stahl, David P. Clark
Chapter 36
Lectures by
John Zamora
Middle Tennessee State University
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Food Preservation
and Foodborne
Microbial Diseases
I. Food Preservation and Microbial Growth
• 36.1 Microbial Growth and Food Spoilage
• 36.2 Food Preservation
• 36.3 Fermented Foods and Mushrooms
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36.1 Microbial Growth and Food Spoilage
• Food spoilage
– Any change in appearance, smell, or taste of a
food product that makes it unpalatable to the
consumer
– Food may still be safe to eat, but is regarded as
unacceptable
• The chemical composition of a food determines its
susceptibility to microbial spoilage
– Perishable
– Semiperishable
– Nonperishable
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36.1 Microbial Growth and Food Spoilage
• Susceptibility to food spoilage is based in large
part on moisture content
– Perishable foods have higher moisture content
than nonperishable foods
• Fresh foods are spoiled by both bacteria and fungi
– Spoilage organisms are those that can gain
access to the food and use the available nutrients
• For example, Escherichia coli frequently
contaminates meat products because it is found in
animals’ digestive tracts
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36.1 Microbial Growth and Food Spoilage
• Growth of Microorganisms in Foods
– Microbial growth follows the normal pattern for
bacterial growth
– Only during the last few population doublings
is food spoilage actually observed
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36.2 Food Preservation
• Methods for slowing spoilage and foodborne
disease
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Cold
Pickling and acidity
Drying and dehydration
Heating
Aseptic food processing
Chemical preservation
Irradiation
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36.2 Food Preservation
• Cold
– Slows microbial growth rate and delays spoilage
– Psychrotolerant bacteria can grow at refrigerator
temperatures
– Freezing allows for longer storage, but isn’t
suitable for all foods
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36.2 Food Preservation
• Pickling and acidity
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pH is an important factor in microbial growth
Most foods are neutral or acidic
At pH <5, most spoilage organisms are inhibited
During pickling process, acetic acid is added to
a solution with sugar or salt
• Pickled foods include pickles, fish, peppers, and
fruits
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36.2 Food Preservation
• Drying and dehydration
– Moisture content (water activity) is critical for
microbial metabolic processes
– Sugar and salt reduce the availability of water
for microbial growth (in effect, dehydrating it)
• Examples: jams, jellies, meats, fish
– Lyophilization (freeze-drying) is the physical
removal of frozen water under vacuum
• Very expensive, but very effective
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36.2 Food Preservation
• Heating
– Used to reduce the bacterial load
(i.e., pasteurization) of a product or to actually
sterilize it (i.e., canning)
– Canning isn’t always 100% effective (Figure 36.2)
• Failure results in swollen cans (DO NOT EAT!)
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Figure 36.2
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36.2 Food Preservation
• Aseptic food processing
– Several foods are now processed and packaged
aseptically
– This food can be stored on shelves for months or
longer
– Involves flash heating and packing in sterile
containers
– Examples: juice boxes and milk substitutes
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36.2 Food Preservation
• Chemical preservation
– Over 3,000 compounds are used as food
additives
– A small number of these are used to control
microbial growth
• Examples: sodium propionate, sodium benzoate,
nitrites
• Some, such as nitrates, are controversial
because studies show they may be harmful to
human health
– Significantly extends shelf life of finished foods
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36.2 Food Preservation
• High-pressure processing (HPP; Figure 36.3)
– High hydrostatic pressure to kill pathogens and
spoilage organisms
– Works on fruits, vegetables, ready-to-eat meats,
and juices
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Figure 36.3
Piston under
pressure
Water
Packaged
food
Pressureresistant
vessel
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36.2 Food Preservation
• Irradiation
– Food is irradiated with ionizing radiation to
reduce bacterial, fungal, and insect
contamination
– Uses gamma or beta radiation, or X-rays
– Irradiated foods must be labeled (Figure 36.4)
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Figure 36.4
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36.3 Fermented Foods and Mushrooms
• Many common foods are preserved, produced, or
enhanced by the actions of microbes
– Fermentation is the anaerobic catabolism of
organic compounds (generally carbohydrates)
– Important bacteria in the fermented food industry
are lactic acid bacteria, propionic acid bacteria,
and acetic acid bacteria
– Products of fermentation include yeast bread,
cheese, yogurt, buttermilk, sausage, sauerkraut,
and soy sauce (Figure 36.5)
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Figure 36.5
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36.3 Fermented Foods and Mushrooms
• Dairy Products
– Include cheese, yogurt, buttermilk, and sour
cream
– Lactic acid bacteria are added to the milk and
the fermentation proceeds for a certain time
period
– Some products require a second fermentation
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36.3 Fermented Foods and Mushrooms
• Meat Products
– Sausages are made from pork, beef, and poultry
• Blend of meat, salt, and seasonings
• Lactic acid bacteria are added to the mixture
• After fermentation, sausages are smoked and
dried
– Fish, often mixed with rice, shrimp, and spices
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36.3 Fermented Foods and Mushrooms
• Vegetables and Vegetable Products
– Sauerkraut (fermented cabbage)
– Pickles (fermented cucumbers)
– Olives, onions, tomatoes, peppers, and many
fruits are also fermented
– Vegetables are often fermented in salt
solutions
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36.3 Fermented Foods and Mushrooms
• Soy sauce (Figure 36.6)
– Complex fermentation product of soybeans and
wheat
– Fermentation for 2 to 4 months in large vats
• Vinegar
– Conversion of ethyl alcohol to acetic acid
(Figure 36.7)
– Acetic acid bacteria include Acetobacter and
Gluconobacter
– Processes for production: open vat (Orleans)
method, trickle (quick vinegar) method, and bubble
method
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Figure 36.6
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Figure 36.7
Cytochrome o
Proton motive force
Ethanol
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Alcohol
dehydrogenase
Aldehyde
Acetaldehyde dehydrogenase
Acetic acid
36.3 Fermented Foods and Mushrooms
• Mushrooms (Figure 36.9)
– Commercially grown mushroom is the
basidiomycete Agaricus bisporus
• Generally cultivated in “mushroom farms”
– Another widely cultured mushroom is the
shiitake, Lentinus edulus
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Figure 36.9
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II. Foodborne Disease, Microbial Sampling,
and Epidemiology
• 36.4 Foodborne Diseases and Microbial Sampling
• 36.5 Foodborne Disease Epidemiology
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36.4 Foodborne Diseases and Microbial
Sampling
• Food poisoning (also called food intoxication)
– Disease that results from ingestion of foods
containing preformed microbial toxins
– The microorganisms that produced the toxins do
not have to grow in the host
• Food infection
– Microbial infection resulting from the ingestion of
pathogen-contaminated food followed by growth
of pathogen in the host
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36.4 Foodborne Diseases and Microbial
Sampling
• Microbial Sampling for Foodborne Disease
– In addition to nonpathogenic microorganisms,
pathogenic microorganisms may be present in
fresh foods
• Rapid detection methods have been developed to
look for the presence of some of these pathogens
(e.g., E. coli O157:H7)
• Tests are molecular and immunology based
• In the U.S., foodborne outbreaks are reported to
the CDC
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36.5 Foodborne Disease Epidemiology
• Clusters of cases caused by microorganisms
in a single source of food
• Widespread multiple disease outbreaks
caused by processing plant or food
distribution center
• Spinach and Escherichia coli (0157:H7)
– E. coli (0157:H7) well studied (Figure 36.11)
and quickly traced
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Figure 36.11
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III. Food Poisoning
• 36.6 Staphylococcal Food Poisoning
• 36.7 Clostridial Food Poisoning
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36.6 Staphylococcal Food Poisoning
• Food poisoning is often caused by toxins produced
by Staphylococcus aureus (Figure 36.12)
– S. aureus can grow on common foods, and some
strains produce heat-stable enterotoxins
– Gastroenteritis occurs within a few hours of
consumption
• It is estimated that 185,000 cases of staphylococcal
food poisoning occur each year
• Enterotoxins of S. aureus classified as
superantigens produce large T cell response and
an inflammatory response
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Figure 36.12
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36.7 Clostridial Food Poisoning
• Clostridium perfringens (Figure 36.13) and
Clostridium botulinum cause serious food
poisoning
– Produce endospores that may not be killed during
cooking/ canning process
• C. perfringens is the most commonly reported form
of food poisoning, with 248,000 annual cases
– Large numbers of cells (>108) must be ingested
– Enterotoxin is produced in the intestinal tract 6–15
hours after consumption
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Figure 36.13
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36.7 Clostridial Food Poisoning
• Botulism is a severe and often fatal food
poisoning
– Caused by an exotoxin produced by Clostridium
botulinum
– Botulinum toxin is a neurotoxin, but is destroyed
by heat
– Average of 24 cases annually (Figure 36.14)
– 16% of cases are fatal
– Home-prepared foods are a common source of
illness
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Figure 36.14
100
Infant
botulism
90
80
70
Cases
60
50
40
30
Outbreaks caused
by fermented
fish/seafood
products, Alaska
20
Foodborne
botulism
10
1985
Outbreak
caused by
baked
potatoes,
Texas
1990
1995
2000
Year
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Outbreak caused by
chili sauce, Texas
2005
2010
IV. Food Infection
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36.8 Salmonellosis
36.9 Pathogenic Escherichia coli
36.10 Campylobacter
36.11 Listeriosis
36.12 Other Foodborne Infectious Diseases
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36.8 Salmonellosis
• Salmonellosis is a gastrointestinal illness caused
by foodborne Salmonella infection
– 40,000–45,000 documented cases per year
(Figure 36.15)
– Chickens and pigs may harbor Salmonella
– Onset of the disease occurs 8–48 hours after
ingestion
– Disease normally resolves in 2–5 days
• Salmonella ingested in food or water invades
phagocytes and grows as an intracellular pathogen
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Figure 36.15
72
64
Cases (in thousands)
56
48
40
32
24
16
8
0
1975
1980
1985
1990
1995
Year
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2000
2005
2010
36.9 Pathogenic Escherichia coli
• Most E. coli are nonpathogenic
• All pathogenic strains are intestinal parasites, and
a few produce potent enterotoxins
– Shiga toxin–producing E. coli (STEC), formerly
called enterohemorrhagic E. coli (EHEC,
i.e., O157:H7), produce verotoxin
– Verotoxin causes bloody diarrhea and kidney
failure
• Other types of E. coli are enterotoxigenic (ETEC),
enteroinvasive (EIEC), and enteropathogenic
(EPEC)
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36.10 Campylobacter
• Campylobacter spp. (Figure 36.16)
– Common cause of bacterial foodborne infections
in the United States
– More than 2,000,000 cases of bacterial diarrhea
per year
– Transmitted to humans via contaminated food
• Poultry, pork, raw shellfish, or in surface waters
• Campylobacter replicates in the small intestine
• Cause high fever, headache, malaise, nausea,
abdominal cramps, and bloody stools
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Figure 36.16
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36.11 Listeriosis
• Listeria monocytogenes (Figure 36.17) is the
cause for listeriosis
– May lead to bacteremia and meningitis
– No food product is safe from contamination
– Psychrotolerant
• L. monocytogenes is an intracellular pathogen
– Uptake of the pathogen by phagocytes results in
the growth and proliferation of the bacterium
• Mortality rate of listeriosis is 20%
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Figure 36.17
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36.12 Other Foodborne Infectious
Diseases
• Other Bacteria
– Yersinia enterocolitica causes foodborne
infections due to contaminated meats and dairy
products
• Can lead to life-threatening enteric fever
– Bacillus cereus grows in food that is cooked and
left to cool slowly
• Causes diarrhea and vomiting
– Shigella spp. cause nearly 100,000 cases of
severe foodborne invasive gastroenteritis
each year
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36.12 Other Foodborne Infectious
Diseases
• Viruses
– The largest number of annual foodborne
infections are thought to be caused by viruses
• Noroviruses (Figure 36.18) are responsible for
most infections
• 9,000,000 annual cases of foodborne disease
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Figure 36.18
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36.12 Other Foodborne Infectious
Diseases
• Protists
– Important foodborne diseases are caused by
Giardia intestinalis, Cryptosporidium parvum, and
Cyclospora cayetanensis (Figure 36.19)
– Can be spread in foods contaminated by fecal
matter in water used to wash, irrigate, or spray
crops
– Fresh fruits are often the source of these infections
– Toxoplasma gondii can be spread by raw or
undercooked meat
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Figure 36.19
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36.12 Other Foodborne Infectious
Diseases
• Prions
– Proteins that adopt novel conformations that
inhibit normal protein function and cause
degeneration of neural tissue (Figure 36.20)
– “New variant Creutzfeldt–Jakob Disease”
• Linked to bovine spongiform encephalopathy
(BSE), a prion disease
– 180,000 European cattle have been diagnosed
with BSE
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Figure 36.20
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