food microbiology - michigan
TRANSCRIPT
FOOD MICROBIOLOGY
By: Kimberly Le
Background Information
Microbiology: the study of microorganisms/
microbes which are a diverse group of simple
life-forms including bacteria, archaea, algae,
fungi, protozoa's, and virus.
Food Microbiology: the study of
microorganisms that inhibit, create, or
contaminate food.
◦ The foods we eat are rarely sterile, they
carry microbes that interact with food.
Microbes in food may display their
presence in several ways:
◦ They can cause food spoilage
◦ They can cause foodborne illnesses
◦ They can transform food’s properties in a
beneficial way (food fermentation)
Antonie van Leeuwenhoek,
first scientist to observe and
describe microorganisms.
Also designed the first
microscope.
Louis Pasteur, father of food
microbiology. Created
pasteurization (prevent food
spoilage) and developed
vaccines.
This Photo by Unknown Author
This Photo by Unknown Author
This Photo by Unknown Author
Food Spoilage
According to the Food and
Agriculture Organization
(FAO), an estimated 1/3 of
the food produced globally is
either lost or wasted,
amounting to 1.3 billion tons
per year.
◦ According to the Oxford dictionary, to spoil is to
“deprive of good or effective qualities”.
◦ Food characteristics change when spoiled and is no
longer acceptable for consumption. Spoiled does not
always come from microbiological in origin but the
majority is caused by microbial activity. (Ex: insect
damage, drying out, discoloration, staling or rancidity.)
◦ Visible microbial growth on surface of food product
(slime or colonies), loss of texture, or chemical
production of microbial metabolism (gas,
pigmentation, off-odors, and flavors) are indicators.
◦ Spoilage is an indicator of quality. An individual may
view it as unacceptable while the other does not due to
social or cultural views. (Ex: matured cheese or game
birds)
Foodborne Illnesses ◦ The World Health Organization (WHO) defines foodborne disease as “Any disease of an infectious or toxic nature caused by, or
thought to be caused by, the consumption of food or water”.
◦ Foodborne illnesses (also known as food poisoning) are commonly caused by different types of bacteria and symptoms vary
among different types.
◦ Most common symptoms include nausea, vomiting, stomach cramps, and diarrhea. Maybe severe or sometimes life threatening.
◦ Five common germs that cause illnesses in the United States according to CDC:
◦ Norovirus
◦ Salmonella
◦ Clostridium perfringens
◦ Campylobacter
◦ Staphylococcus aureus
◦ Three that are considered zero tolerance (potentially dangerous at any level when ingested, does not cause illness but are more
likely to lead to hospitalization):
◦ Salmonella
◦ E.coli
◦ Listeria monocytogenes
Norovirus (NoV)
◦ There are at least 33 different norovirus genotypes but
there are only 3 genogroups that infect humans.
◦ Very contagious virus that causes projectile and explosive
vomiting, followed by diarrhea among people of all ages.
A person usually develops symptoms 12 to 48 hours after
exposure and the symptoms may last 1 to 3 days.
◦ Able to contract the virus by direct contact with an
infected person, consuming contaminated food or water,
or touching a contaminated surface.
◦ Common settings of outbreaks includes healthcare
facilities, restaurants, schools, childcare centers, and
cruise ships.
◦ Sources:
◦ Contaminated water
◦ Seafood
◦ Meat
◦ Fruit and vegetables
This Photo by Unknown Author is licensed under CC BY-SA-NC
According to the CDC,
there are about 2,500
reports of Norovirus
outbreaks each year in the
US. Most common from
November to April.
Leading
cause of
foodborne
illness in
the US
Salmonella◦ A motile, non-spore forming, gram negative, rod-
shape bacterium.
◦ Divided into two species: S. enterica and S. bongoriwith subspecies but is further subdivided by serotypes.
◦ Can cause two types of illnesses, depending on serotype: nontyphoidal and typhoid.
◦ Typhoid (S. Typhi and S. Paratyphi A. which is found only in humans)
◦ Duration is longer than nontyphoidal
◦ Most severe and has a higher rate of mortality
◦ Usually associated with contaminated drinking water
◦ Nontyphoidal (caused by serotypes other than those caused by typhoid)
◦ Sources:
◦ Contaminated water
◦ Food sources (Ex: meat, poultry, eggs, milk, fish, produce, etc.)
◦ Cross contamination
This Photo by Unknown Author is licensed under CC BY-ND
This Photo by Unknown Author is licensed under CC BY-SA
Growth of Salmonella on Xylose
Lysine Deoxycholate agar (XLD)
plate.
Salmonella bacterium
This Photo by Unknown Author is licensed under CC BY-SA
Bacteria was
discovered by an
American
scientist, Daniel
E. Salmon in
1885.
Salmonella is more
common in the summer
due to warmer weather
and unrefrigerated foods
creating an ideal
condition for the bacteria
to grow.
Clostridium perfringens
◦ Anaerobic (but aerotolerant), gram positive, spore-forming rod
that produces an enterotoxin.
◦ Non-pathogenic C. perfringens is distributed in the environment
and is found in the intestines of humans.
◦ Can take on 2 forms in foodborne illnesses:
◦ Gastroenteritis form
◦ Common and self limiting
◦ Depending on strain, can cause more severe damage
◦ Enteritis necroticans (“pig-bel disease”)
◦ Rare in the US
◦ More severe than other form of illnesses and often fatal
◦ Sources:
◦ Raw meats and poultry
◦ Dried or pre-cooked foods
◦ Prepared food in large quantities and kept warm a long time
◦ Vegetable products
◦ Spices and herbs
This Photo by Unknown Author is licensed under CC BY-SA
C. perfringens under the microscope
This Photo by Unknown Author is licensed under CC BY-SA
C. Perfringens on egg yolk agar plate
All Clostridium
species have
peritrichous flagella
with an exception of
C. perfringens
This Photo by Unknown Author is licensed under CC BY-SA
Spores can persist in soil,
sediments, and areas subject to
human or animal fecal pollution
Campylobacter◦ Non-spore forming, gram negative, rod with a curve or S
shaped morphology, and a flagellum at one or both ends of the
bacterium.
◦ Are microaerophilic (grow at lower than atmospheric oxygen
concentration), causing them to be fragile in an ambient
environment.
◦ More than 80% of the infection are caused by C. jejuni.
◦ Common in low-resource countries
◦ Many animals can show no signs of illness as the bacteria is
carried throughout the body and can be transferred to edible
parts when an animal is slaughtered.
◦ Fruits and vegetables can be contaminated through contact
with the soil or water containing feces from other animals.
◦ Sources:
◦ Improper handling or undercooked poultry products
◦ Unpasteurized milk and cheese
◦ Contaminated water
◦ Vegetables
◦ Seafood
This Photo by Unknown Author is licensed under CC BY-SA
This Photo by Unknown Author is licensed under CC BY-NC
Blood Agar Plate
Campylobacter Bacteria
Third leading
bacterial cause
of foodborne
illness in the
U.S.
Pets can carry the
Campylobacter
bacteria and other
germs that can make
you sick.
Staphylococcus aureus
◦ Gram positive, non-motile, small spherical bacteria, appears in
chains or grape like clusters, and can produce heat stable
enterotoxins.
◦ A gastrointestinal illness caused by eating food contaminated
with toxins produced by Staph bacteria
◦ Staph bacteria can be killed in cooking, but the toxins are not
destroyed which will still be able to cause illness.
◦ Food contaminated with the toxin may not smell bad or look
spoiled.
◦ Common contamination by Staph is due to the handling of
food with unwashed hands
◦ About 25% of people and animal have Staph on their skin and
in their nose, which usually does not cause illness.
◦ Source:
◦ Widely distributed in the environment (Ex: air, dust, food, surfaces, animals, humans, etc.)
◦ Meat, meat products, poultry, and egg products
◦ Bakery and dairy products
◦ Contamination when handling food products
This Photo by Unknown Author is licensed under CC BY-SA-NC
This Photo by Unknown Author is licensed under CC BY-SA
Staph bacteria under microscope
Staph colonies on a TSA plate
Staphylococci are
mesophilic and the
optimum temperature
of growth for S.
aureus is 35°C
Strains of S.
aureus are highly
tolerant to salts and
sugars
Escherichia coli (E.coli)◦ Toxin-producing Shiga-toxigenic E.coli (STEC) are Gram
negative, rod-shaped bacteria, with peritrichous flagella.
◦ A subset of STEC which is enterohemorrhagic
Escherichia coli (EHEC) includes O517:H7 which is the
predominant strand that accounts for 75% of EHEC
infections worldwide.
◦ E.coli 0517:H7 is common in North America and was first
identified in 1982.
◦ Less is known about non-O517 STEC subgroups but
cause a less severe illness than O517.
◦ Some people can get less serious infections (range to no
symptoms to diarrhea) but the infection can progress into
life threating form of the illness such as kidney failure.
◦ Sources:
◦ Raw or undercooked ground beef
◦ Unpasteurized milk or fruit juice
◦ Acidic foods
◦ Contaminated water
◦ Vegetables (Ex: sprouts, lettuce, and spinach)
This Photo by Unknown Author is licensed under CC BY-ND
This Photo by Unknown Author is licensed under CC BY
E.coli and M. luteus on TSA plate
E. coli bacterium
Around 5-10% of
those diagnosed with
STEC can develop
hemolytic uremic
syndrome (HUS)
which effects the
kidneys.
STEC live in the gut
of ruminant animals
and the major source
for human illnesses is
cattle. STEC does not
generally make
animals sick but they
are able to pick up
STEC from the
environment and may
spread it.
Listeria monocytogenes
◦ Gram positive, rod-shaped, facultative bacterium, and motile by flagella.
◦ Leading cause of death from foodborne illness. (3rd in the US)
◦ Is salt tolerant, can grow and survive in temperatures below 1°C.
◦ Can cause two forms of disease:
◦ Non-invasive: gastrointestinal illness that resolves
◦ Invasive form: may cause septicemia and meningitis
◦ Pregnant women, people with weak immune systems and the elderly are more susceptible to infection than most other people
◦ Source:
◦ Moist environments, soil, and decaying vegetation
◦ Raw milk, cheese, ice-cream
◦ Raw poultry and meats
◦ Contaminated surfacesThis Photo by Unknown Author is licensed under CC BY-SA
This Photo by CDC website
Listeria monocytogenes bacteria
Colonies on blood agar plate
Pregnant women are 10 times
more likely than other people to
get the infection. It can pass on
to their newborns and may
cause miscarriages, stillbirths,
preterm labor, serious illnesses
and even death.
Foods to avoid according to the CDC:
• Queso fresco and other soft
cheeses
• Raw sprouts
• Melons
• Hot dogs, lunch meat and cold cuts
• Smoked meats
• Unpasteurized milk
Food Fermentation
◦ Microbes play a positive role in food by changing its properties so that it is beneficial.
◦ Majority of fermented foods are produced by:
◦ lactic acid bacteria (Ex: fermented meats, vegetables, and dairy products)
◦ Lactobacillus species
◦ Leuconostoc species
◦ Pediococcus species
◦ Yeast
◦ Saccharomyces cerevisiae (used in bread products)
◦ Kluyveromyces marxianus (dairy products)
◦ The group of organisms can grow under conditions of low pH and reduce water activity.
◦ Lactic acid bacteria have antimicrobial activity since they can inhibit other micro-organisms to improve quality and safety of food products (act as a food preservative).
◦ These foods consumed are termed “probiotics” since they help balance gut bacteria and improve health.
This Photo by Unknown Author is licensed under CC BY-SA
Élie Metchnikoff is a
Russian zoologist, the
founder of the theory
phagocytic immunity,
and studied probiotics,
fermented dairy foods
and health. Élie Metchnikoff circa 1908
Examples of fermented foods
Prevention◦ 4 steps at home for food safety
◦ Clean (wash hands and surfaces often)
◦ Separate (raw food products away from ready to eat foods)
◦ Cook (temperature is important to kill harmful bacteria)
◦ Chill (refrigerate and thaw foods safely)
◦ Always wash your hands to prevent harmful germs getting onto the food
◦ Cook food thoroughly at high enough temperatures to kill germs
◦ Do not eat raw batter or dough and other foods with uncooked eggs or flour
◦ Wash fruits and vegetables before consuming
◦ Bacteria can multiply rapidly if left at room temperature or in the Danger Zone between 40-140F. Do not leave food out for more than 2 hours (or 1 hour if its hotter than 90F outside)
◦ Keep an eye out for recalled food products and immediately dispose of them
◦ More info about food safety and recalls visit: https://www.cdc.gov/foodsafety/index.htmlhttps://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts
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Food and Drug Administration (2012). Bad Bug Book, Foodborne, Pathogenic Microorganism and Natural Toxins. 2nd edition.
https://www.fda.gov/media/83271/download
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Hammond, A. (2019 June 2). Louis Pasteur: "The Father of Microbiology" Who Pioneered Vaccine Science. Foundation for Economic Education.
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