Chapter
32: Principles of Food Microbiology
I. PRINCIPLES
OF FOOD MICROBIOLOGY
A. Food
is an ecosystem in which microorganisms compete to metabolize
the nutrients, making endproducts such as acids, alcohols and gas.
1. Food supplies energy & the chemical
building blocks of life
B.
Microbes are responsible for manufacturing, via their biochemical
activities, much of the foods we
enjoy.
1. Foods that have been intentionally altered by
carefully
controlling the activity
of bacteria, yeasts or molds are called
fermented.
a. e.g. yogurt, buttermilk, and cottage cheese
are produced
by the
activities of lactic acid bacteria.
b. bread rises due to the activities of yeasts.
c. blue cheese is produced by the activities of
molds.
d. Many people enjoy ethyl alcohol, which is the
metabolic
waste, or
urine equivalent, of yeast.
2. Microbes also preserve foods so that we can
enjoy them at a
later date.
3. Microbes are vital to maintaining the
fertility of the soil.
C.
Microbes are responsible for the direct loss of much food through…
1. Destruction of the crops and animals from
whence the food
comes
2. Biochemical changes in foods, which, when
perceived as
unpleasant, are called
spoilage.
a. Spoilage
can be delayed or prevented and foodborne
illness can
be avoided by the slowing the growth of
microorganisms,
or by reducing or eliminated the initial
numbers of
them on food.
b. Growth of pathogens generally does not result
in
perceptible
changes in quality of food, but, can result in
foodborne disease.
II. FACTORS
INFLUENCING THE GROWTH OF MICROOROGANISMS IN
FOODS
A. Intrinsic
and extrinsic factors together determine which microorganisms
can grow and eventually predominate
in a food product.
B.
Intrinsic Factors
1. Bacteria require a high aw (water availability). They grow
quickly on fresh,
moisture rich foods but not on dry, sugary or
salted foods.
a. Fungi can grow on foods which have an aw too low to
support the
growth of bacteria.
2. The pH of a food is important in determining
which organisms
can survive and thrive
on it; many species of bacteria, including
most pathogens, are
inhibited by acidic conditions.
a. This is why products that are made from
tomatoes
(ketchup,
tomato sauce, etc.) are less likely to spoil.
3. Rinds, shells, and other coverings aid in
protecting some foods
from the invasion of
microorganisms.
4. Some foods contain natural antimicrobial chemicals
that may
help prevent spoilage.
a. The browning of fruits, such as apples, after
we damage
their skin
is actually an antimicrobial
action.
C.
Extrinsic Factors
1. Low temperatures halt or inhibit the growth
of most foodborne
microorganisms.
a. However, psychrophiles
are able to grow at refrigeration
temperatures.
2. The presence or absence of oxygen impacts the
type of
microbial population
able to grow on a food. Excluding oxygen from
a food prevents the growth
of obligate aerobes but enables the
growth of obligate
anaerobes, including Clostridium botulinum.
III. Food and History – Food has played a critical
role in history
A.
You may have been taught about the Spice
Trade that resulted in an
intense burst of exploration. Actually, microbes provided the impetus for
those journeys.
1. In the Middle Ages, foods like meat, milk,
etc. spoiled quickly,
particularly on warm
days.
a. Even spoiled meat is nutritious despite its
rank odor &
bad
taste, & it beat starving by a long stretch.
b. If you added spices to the rotting meat, the
strong flavor
covered the
rotten aroma.
c. The spice trade relied upon camels &
small, leaky boats
to transport
spices from the far east. This was very
expensive.
d. From the 1400 to 1600s, there was an
exploration
explosion in
an effort to find a better, quicker, cheaper route.
1) You could credit microbes with the discovery
of
B.
Another role of microbes in the Middle Ages was producing miracles!
1. Damp, dank churches were perfect incubators
of Serratia
marcescens on the sacramental wafers. This bacterium produces
a bright
red pigment that resembles blood, hence the appearance
of
blood-covered holy bread… a miracle.
IV. FOOD
PRESERVATION
A. Food
spoilage can be eliminated or delayed by destroying
microorganisms or altering
conditions to inhibit their growth.
1. Methods used to preserve foods include:
canning,
pasteurization, cooking,
freezing, refrigeration, reducing the aw,
lowering the pH, adding
antimicrobial chemicals and irradiation.
B.
HEAT STERILIZATION
1. One of the problems with war is that soldiers
insist on being fed
regularly. In the early
1800s, Napoleon found that the joy of his life,
his large army, could no
longer feed itself by stealing from the local
peasants
and thus his plans to conquer the world were stalled.
a. His solution was to offer a reward for anyone
who could
figure out
how to preserve food so he could take it along with
his army.
b. In 1810 a man by the name of APPERT found that if he
put
food in a bottle, jammed a cork tightly in it and placed it
in
boiling water for an hour or so the contents didn't spoil.
BINGO!!,
he won the prize, Napoleon got his war, and
learned
just how seriously cold a Russian winter could get.
2. This procedure, known as STERILIZATION, eventually
developed
into the canning process. In sterilization, all living
organisms
are destroyed, including bacterial spores. As you will
learn
later, the most deadly biological toxin is produced by the
spore-forming
bacterium, Clostridium botulinum.
a. C. botulinum
is an obligate anaerobe that can grow in
sealed
containers like cans and jars, therefore the canning
process
is specifically designed to destroy the C. botulinum
spore.
b. This
is achieved by heating food to a minimum of 123oC
or 253.4oF
for 15 minutes.
3. In the home, sterilization is carried out
using a PRESSURE
COOKER. Many of you
probably have seen your grandmother, or
perhaps your mother,
using this container to sterilize home-canned
food. The pressure
cooker works as follows:
a. A pint or so of water is placed in the bottom
of the
pressure cooker.
b. The food to be sterilized is placed in the
container with
the lids
loose.
c. The top is placed on tightly and the water is
brought to a
boil until
all the air is vented through the outlet port.
d. Then a weight is placed on the outlet port.
This weight is
adjusted so
that steam will only escape once the pressure
has reached
15 pounds per square inch. At this pressure the
temperature
will reach 123oC at sea level.
e. Once this temperature is reached and steam
begins to
bleed from
the port, heating is continued for a period of time
necessary to
bring all the food in the containers to 123oC for
15 to 20
min.
f. The heat is turned off and the contents are
allowed to
cool.
g. Finally, the pressure cooker cover is
removed, and the jar
lids
tightened immediately to prevent contamination from
entering.
4. In the microbiology laboratory and commercial
canning
companies
sterilization is achieved by using large containers that
operate
exactly the same as the home pressure cooker. The
laboratory
instrument is called an AUTOCLAVE. In
commercial
canning
processes the sterilization containers may be as large as
rooms and
the food is often wheeled in on large carts.
C. COOLING AND FREEZING
1. Except for Eskimos and other inhabitants of
the far north,
cooling has only emerged
as a common means of preserving food
since the mid 1800s when
the ice-making machine was discovered.
a. Prior to that time it was common in northern
climes for
people to
cut large blocks of ice from local lakes and to store
them in
insulated warehouses for use during the summer
months to
cool their beer and other food items.
b. In the
available
for ~ the last 60 years.
2. Cooling as a food preservative is utilized at
two levels, 7 to 4oC
and -20oC or
lower.
a. The higher temperature is commonly used in
home
refrigerators.
1)
At this temperature, the growth of microbes is
slowed down but not stopped.
Food will spoil if left in
the refrigerator for extended periods
of time.
b. At the lower temperature the food is frozen.
1)
As microbes are unable to grow in frozen material,
freezing is one of the most successful
means of
preserving food with minimal change in
flavor or loss
of nutritional value.
2)
The major draw back to the use of cooling is that
(a) it is expensive
(b) it also preserves many pathogens that
happen to be present in the food when
it was
cooled.
D.
DRYING – as a
means of preserving food may very well be the oldest
method
of preservation known to man.
1.
Dried food doesn’t spoil, it is light, and it stays unspoiled as long
as it remains dry.
a.
It requires little technology… fresh meat could be dried by
placing it in the hot sun, or it could
be hung over sticks by a
campfire.
2.
As the water evaporates and the food dries, the OSMOTIC
PRESSURE (the result of hydrophilic molecules
binding water
molecules) increases to a point where
microbes are unable to
compete with the water-binding
material in the food for the
remaining water.
a.
Since microbes are unable to grow without free
(available) water, the food is safe
from spoilage, even
though it may retain significant
bound-water.
E. SALTS AND OTHER CHEMICALS
1. SALT (SODIUM CHLORIDE) as a
food preservative is probably
as old as drying, if not
older.
a. All mammals need salt to survive.
b. Our hungry ancestors must have found animals
or fish
that
died in drying pools of salty water.
a.
They quickly recognized that the salted food was
unspoiled and remained so.
c. The salted food served a dual role as a
source of nutrition
and
of sodium chloride, and as it dried it was easier to
transport.
d. Before canning, salted meat was the staple
food on ships
that
traveled any significant distances away from land
(hence
the term "ol salt").
2. NITRATE (NO3) AND
NITRITE (NO2) (SALTPETER) are used in
many foods today as both
a preservative and to prevent meat from
browning.
a. The bacterium Clostridium botulinum is an obligate
anaerobe.
1)
Even a tiny amount of free oxygen prevents its
growth.
2) C.
botulinum readily grows in prepared meats
like
sausage,
bologna, hot dogs, etc.
b.
Nitrate and nitrite are OXIDIZING AGENTS that are
chemically similar to oxygen,
inhibiting the growth of C.
botulinum
in foods.
c.
Saltpeter also prevents certain substances in meat from
becoming REDUCED, causing them to turn
the meat brown.
1) People think brown meat must be of poor
quality.
d.
In recent years scientists have discovered a link between
nitrate/nitrite and the formation of
carcinogens.
1)
The FDA has therefore required the removal
of these chemicals from foods (if
possible) and the
lowering of their concentration to the
minimal level.
3. SULFITE (SO2) and VITAMIN C prevent
the "BROWNING" of
fruits and vegetables.
a.
Generally, people feel that "brown" food items are spoiled
or at least of lower quality.
1)
When fruits and veggies are exposed to oxygen
through damage, enzymes produce
brown-colored
chemicals that are inhibitory to many
microbes.
b.
Sulfite is a powerful reducing chemical that blocks the
browning
response, and it is inexpensive and effective
in tiny
amounts.
1)
It is common to rinse fruits and vegetables in
restaurants in solutions containing sulfite.
2)
This insures that items that were prepared several
hours before will remain
"fresh-looking" all day long
on the customer's plates.
3)
At the concentrations used, sulfite is not toxic, but
a small percentage of people are highly allergic to
sulfite and an exposure to even a tiny
quantity of it on
lettuce etc. may be sufficient to
induce a violent
allergy attack.
4)
Restaurants often have signs telling their
customers that they are using sulfite
on their foods.
c. Another powerful reducing agent that serves
the same
purpose
is vitamin C (ascorbic acid).
1)
This vitamin also is inexpensive, is effective in
small amounts, plus it is beneficial
to those who
ingest it.
2)
Because it is more expensive than sulfite and it
tends to decay faster, it is not
universally used.
4. ORGANIC ACIDS: As you recall, all microbes require an
optimum pH or acidity in
their environment to grow. If there is too
much acid or base, a
microbe will not grow.
a.
Microbial fermentations produce organic acids as
byproducts.
1)
ACETIC ACID (vinegar)
2) LACTIC
ACID
3) PROPIONIC
ACID it is not too
b.
They can be added to food in sufficient quantities to lower
the pH enough to prevent the growth of
food-spoilage
bacteria.
1)
Thus was born choice food items like yogurt,
sauerkraut, pickles, cheese and
buttermilk.
c.
Artificial acids, like BENZOIC ACID, inhibit the growth of
some molds
1)
It added to breads and other bakery products that
require long shelf live.
5. ANTIBIOTICS are
inexpensive, stable, safe and effective
in small quantities. With their ability
to kill or inhibit many microbes,
they might seem the
perfect food preservative.
a.
However, all
is not what it seems. Using antibiotics for
food preservation is like using 100
dollar bills for toilet paper.
b.
We are in grave danger from infections produced by
antibiotic-resistant microbes.
c.
The use of antibiotics in preserving food and in animal
feeds has been demonstrated to
increase the spread of
antibiotic resistance between
pathogens.
F.
RADIATION is
becoming widely used in the preservation of food.
1.
In 1997 the FDA approved radiation as a means of preserving
meats.
a.
Many of the prepared meals available on the supermarket
shelves at room temperature have been
sterilized by
radiation.
b.
In the
2.
To sterilize food by this technique, the food is placed in a
protected room and exposed to a high
dose, usually of gamma
radiation, from radioactive wastes
refined from atomic power plants.
a. This even kills viruses and bacterial
spores.
3.
Using irradiation to destroy contaminating microbes slightly
increases food packaging costs, but
the cost is offset by the
resulting extended shelf life
4. FAQ: Does exposure to radiation make the food
radioactive?
a. No. There is no residual radiation
contaminating food
exposed
to sterilizing doses of radiation.
Does the treatment produce dangerous chemicals in the
radiated
food?
a. The vast majority of the scientific evidence
does not
support this
contention.
b.
There is no doubt that the high radiation does induce
some chemical changes in the food, but
there is no proof
that any of these materials are
harmful.
Would you eat radiation treated foods?
a. Yes.
However, I consider every new technology suspect
until long
use proves otherwise, so I try to keep myself
informed on
this and other technological
matters; I would
advise that
you do the same.
1. Pickling involves the addition of salt to
change the environment
so that different
microbes can grow and change the flavor of the
food in a preferred way.
a.
The fermentation carried out by these microbes produces
organic acids. This preserves the food.
1) It relies upon naturally occurring lactic
acid
bacteria.
b.
Pickles and sauerkraut are produced this way.
2.
Sugar is also used in jams and jellies as a preservative.
a.
It acts the same way that salt does by bind up the
available FREE-WATER chemically so
tightly that it is not
available to most microbes.
b.
If you’ve ever found a mass of hairy mold growing in jam
or jellies, you’ve found a saccharophiles
(sugar-loving)
microbe.
H.
SMOKING is another ancient means of preserving food.
1.
Smoking probably developed as an outshoot of drying food by
the campfire.
a.
The smoke gives the food a pleasing flavor.
b.
The foods absorb various chemicals from the smoke,
including aldehydes and acids.
1) Aldehydes are lethal
to many microbes
2) Acids lower the pH of the meat.
2.
There is danger
lurking in this process. Aldehydes are
carcinogenic and people who eat a
heavy diet of smoked foods
suffer disproportionately
from cancer of the mouth, stomach and
esophagus.
V. FOOD SPOILAGE
A. Food
spoilage is most often due to the metabolic activities of
microorganisms as they grow and
utilize the nutrients in the food.
B.
Bacteria
1. Psychrophilic
species of Pseudomonas can multiply at
refrigeration temperatures
and metabolize a wide variety of
compounds.
a. They cause spoilage of many different kinds
of foods
including
meats and vegetables.
2. Erwinia, Acetobacter, Alcaligenes,
lactic acid bacteria, and
endospore
formers are also important causes of food spoilage.
C.
Fungi grow readily in acidic as well as low moisture environments
1. Therefore fruits and breads are more likely
to be spoiled by fungi
than
by bacteria.
VI. MICROORGANISMS IN FOOD AND BEVERAGE
PRODUCTION
A. Fermented
foods are not only perceived as pleasant tasting but the
acids produced inhibit the growth of
many spoilage organisms as well as
foodborne
pathogens.
B.
Lactic Acid Fermentations by the Lactic Acid Bacteria
1. The tart taste of yogurt, pickles, sharp
cheese and some
sausages is due to the
production of lactic acid by species of
Lactobacillus, Lactococcus, Streptococcus, Leuconostoc and/or
Pediococcus.
2. Commercial production of fermented milk
products relies on the
use of starter cultures.
a. The lactic acid produced by the bacteria
causes milk
proteins
to coagulate or curdle, and sours the flavor.
b. Starter cultures, and sometimes rennin, are
added to
pasteurized
milk to make cheese.
c. Acid production and enzyme activity results
in formation
of curds
and whey.
d. Other bacteria or fungi are sometimes added
to ripened
cheese
to impart characteristic flavors or textures.
C.
Alcoholic Fermentations by Yeast
1. The yeast Saccharomyces
ferments sugar to produce ethanol
and carbon dioxide.
2. Wine
is the product of the alcoholic fermentation of naturally
occurring sugars in the
juices of fruit, most commonly grapes, by
specially selected
strains of Saccharomyces cerevisiae.
a. Sulfites are added to inhibit the naturally
occurring
microbial
population of the grape.
3. The production of beer is a multi-step process designed to
break down the starches
of grains such as barley to produce simple
sugars.
a. The sugars serve as a substrate for alcoholic
fermentation
by yeast.
4. Distilled
spirits are produced using distillation to purify the
alcohol generated during
fermentation.
5. Vinegar
is the product of the oxidation of alcohol by the acetic
acid bacteria, Acetobacter and Gluconobacter.
6. In bread
making, the CO2 produced by yeast causes bread to
rise, and the alcohol is
lost to evaporation.
D.
Changes Imparted by Mold
1. Some cheeses and many traditional dishes used
throughout the
world are produced by
encouraging the growth of molds on foods.
2. Soy sauce is made by allowing species of Aspergillus to
degrade a mixture of
soybeans and wheat, which is then fermented
in brine.
VII. FOODBORNE ILLNESS
A. Foodborne
intoxication
1. Foodborne
intoxication is an illness that results from the
consumption of a toxin
produced by a microorganism growing in
a food product.
a. Many strains of Staphylococcus aureus produce a toxin
that, when
ingested, causes nausea and vomiting.
b. Botulism is caused by ingestion of a
neurotoxin produced
by the
anaerobic, spore-forming, Gram-positive rod
Clostridium
botulinum.
1) Boiling food for 15 minutes will destroy this
toxin.
B.
Foodborne Infection
1. Foodborne infection
requires the consumption of living
organisms.
a. Thorough cooking of food immediately before
consumption
will kill bacteria, thereby preventing foodborne
infection.
b. Salmonella and Campylobacter
species are commonly
associated
that are commonly associated with poultry
products.
c. Some epidemics of E. coli O157:H7 have
been traced to
undercooked
contaminated hamburger patties.
C. FOOD BORNE
DISEASE : many pathogens have
evolved to hitch a
ride in
our food, gaining entry into our nutrient-rich bodies for their own
nefarious
ends.
1. Consumers are very concerned about the
contamination of
their
food with dangerous microbes.
a. In one survey 77% indicated that the fear of
"germs"
in
their food was of greater concern than pesticide residues,
product
tampering, antibiotics in food or other safety risks.
2. Despite these concerns, studies show a
significant lack of
knowledge
of consumers as to what constitutes safe food handling
practices.
These studies show:
a.
Most consumers erroneously believe that foodborne
illness
is caused by food prepared commercially rather than
in
the home.
1) In reality, 80% of food poisoning occurs in
the
home.
2) We believe this because an outbreak at TacoTime
gets
on the evening news but Aunt Mary's spoiled
canned
corn often doesn't get that attention (unless it
wipes
out the entire family).
b. Many very intelligent individuals mistakenly
tell people
that food
poisoning symptoms cause no fever & occur within
12-24 hours
after eating spoiled food.
1) The most common causes of US food poisonings,
Salmonella and Campylobacter, may
take several
days
to develop and often cause fevers.
c. Consumers often do not handle food safely at
home as
they are
unaware of the importance of refrigeration,
handwashing, and preventing cross-contamination between
meats and
uncooked foods in preventing foodborne illnesses
in the home.
1) Consumers are usually willing to change their
habits
when provided with the correct information.
d. Food poisoning kills ~9,000 Americans/year
and sends
30 to 80
million to the doctor, emergency rooms or
bathrooms
with fever, diarrhea and cramps.
e. Bacteriological analysis indicates that it is
better to eat
food that
has fallen in your toilet than food that has fallen into
your kitchen
sink.
VIII. What follows is a brief description (by no
means inclusive) of the major
FBD
including the names of the perpetrators, the disease mechanism (when
known),
their prognosis and treatment.
A. BOTULISM
1. CAUSE - an intoxication
from the ingestion of a virulent nerve
toxin produced by the
growth of the gram positive, obligate
anaerobe, spore-former Clostridium botulinum.
a. This bacterium appears to be a normal
inhabitant of the
soil
and thus readily contaminates most foods.
b. It is able to grow in absence of oxygen in a
wide variety
of foods and in so doing produces a protein neural toxin.
1)
Just over 100 grams of this toxin would be
sufficient
to kill every human on earth.
c. The organism will not grow in the presence of
oxygen or
nitrate
salts.
d. It does not produce the toxin at a pH below
4.7.
e. Only one strain, which is found associated
with marine
organisms,
is able to produce the toxin at refrigerator
temperature.
b. The toxin is destroyed by boiling it at 100oC
for 10 to 15
min.
However, the spore requires a temperature of 121oC for
15
min to kill it.
2. DISEASE MECHANISM of botulism
a. The toxin acts by binding to nerve junctions
and
destroying
the nerve.
b. The symptoms usually within 12 to 36 hours,
but can take
up
to 8 days to appear…
1) double vision, dizziness, inability to speak,
breathe
or
swallow.
c. Death often occurs due to the inability to
breath.
3. TREATMENT AND PROGNOSIS of botulism
a. Treatment – establish a clear airway, aid
breathing, give
botulinus anti-toxin, and provide supportive therapy.
1) Respiratory complications require
hospitalization.
2
Antitoxin is only effective against free toxin;
once the toxin has bound to the
nerves the damage is
irreversible.
b. Prognosis – hospital treatment and antitoxin
significantly
lower
mortality. Complications include…
1) long-lasting weakness that persists for up to
8
months
2) nervous system dysfunction for up to one year
4. PREVENTION of botulism
a. The entire canning process is built around
insuring that all
spores of
this bacterium contaminating any canned food are
destroyed in
the sterilization process.
1) Deaths from commercial-botulism are very
rare.
b. The majority of
botulism poisonings occur in HOME-
CANNED FOODS.
1) A rule of thumb is "READ THE BLOODY
CANNING
DIRECTIONS"
and if you think a food
might contain the
botulism toxin never taste even the
smallest drop of
it!
c. NEVER feed raw
honey to a child under the age of
two
because
the botulism spores can grow in the immature gut
and
produce the toxin.
1) This can not occur in the adult due to our
gut
friends,
the normal flora.
B.
Q FEVER
1. CAUSE – an infection by the gram negative,
obligate
intracellular
bacterium Coxiella burnetii.
a.
This organism is associated with farm animals (sheep,
goats,
cattle, dogs, cats, birds, rodents, and ticks), with man
usually
considered to be an accidental victim.
b. Infected animals shed this bacteria in urine, feces,
birth
products, and milk.
c. Humans
infection occurs by inhaling contaminated
droplets excreted by infected animals.
1) Consumption of
raw milk has also been associated
with infection in rare cases.
2. DISEASE MECHANISM of Q fever
a. The incubation period for early (acute) Q
fever is
approximately
20 days.
b. In acute Q fever, the three main sets of
symptoms
include flu-like syndrome, pneumonia and hepatitis.
1) Flu-like symptoms: fever, headache, muscle pains
2) Pneumonia symptoms: fever, cough, chest pain
upon
breathing, shortness of breath (occurs in up to
1/3 of
patients)
3) Hepatitis symptoms: jaundice, clay colored stools,
fever
c. Chronic Q fever develops in individuals
who have been
infected for over 6 months without effective treatment.
1) Its main
feature is infection of the heart valves
termed endocarditis.
2) Symptoms: prolonged fever, night sweats, chills,
fatigue, shortness of breath
3. PROGNOSIS of Q fever
a. The flu-like syndrome is usually self-
limited.
1) It lasts up to
three weeks.
2) For people who get treatment in the early
stages
of
Q fever, prognosis is generally good.
b. Chronic Q fever requires prolonged treatment
with
antibiotics
and frequent monitoring for relapses.
4. TREATMENT of Q fever
a. Antibiotic therapy
5. PREVENTION of Q fever
a. People at risk (e.g., farmers, veterinarians)
should adhere
to
adequate disinfection and disposal of potentially infectious
animal
products.
b. Pasteurization of milk can also help
prevent Q fever.
1) The temperature of the pasteurization process
was
increased
a few years ago to 72oC for 15 seconds to
eliminate
it from milk.
C. STAPHYLOCOCCUS
AUREUS FOOD POISONING
1. CAUSE - the gram positive coccus-bacterium
Staphylococcus
aureus
a.
S. aureus
is a common inhabitant of human skin and
noses; it is considered part of our
natural flora.
1) It is a common cause of nosocomial infections
that
frequently causes death in the patients it infects
2)
it is a prevalent cause of severe skin infections like
boils and impetigo
3)
it is the etiological agent of TOXIC-SHOCK
SYNDROME
b.
Although it is not a spore-former, it does tolerate high
temperatures better than most
non-spore-formers.
c.
It is able to grow in high salt and sugar environments.
1) It generally produces FBD in "rich
foods", such as
cakes,
pies, potato salad and custards.
2) The usual scenario involves food that was
prepared
in advance and improperly stored for a long
time
before being eaten.
3) The bacteria grow rapidly, often in such
perfusion
that
their yellow colonies can be observed upon close
examination.
2.
DISEASE MECHANISM of Staph food poisoning
a. During growth the bacteria produce a number of
potent
toxins,
one of which, called a SUPERANTIGEN, mimics a
protein
involved in our immune response.
b.
This superantigen acts by over stimulating the
T-cells to
produce prodigious quantities of
interleukin 2
c.
Interleukin 2 induces fever, malaise, nausea, vomiting,
diarrhea and shock
1) These are are the
classical symptoms of Staph
food
poisoning.
d.
S. aureus
tends to carry a large number of antibiotic
resistant plasmids.
e.
Staph food poisoning symptoms usually appear within 1
to 6 hours after ingestion.
3. PROGNOSIS of Staph food poisoning
a. The disease is usually over within 24 hours
and death is
rare,
usually limited to the very young or the old and
infirmed.
4. PREVENTION of Staph food poisoning
a. Wash hands before preparing food
b. Store foods in refrigerator prior to serving
1.
CAUSE - Salmonella are a genus of gram negative, small rod-
shaped, non-spore-forming
bacteria that are usually associated
with animals, both wild
and domestic.
a. This is one of
the most common causes of foodborne
illnesses in US homes.
1)
During the slaughter and preparation of food for
human consumption, fecal material can
contaminate the food.
2)
The
most common sources of salmonella infection
are turkey, chicken, beef etc. and eggs .
3)
Such
contamination can easily be spread to other
foods via kitchen utensils, cutting boards,
by
contaminated hands or contact with
contaminated
work surfaces.
b. Salmonella strains can occur in the
digestive tracks of
snakes, turtles and
lizards, as well as chickens, horses, and
turkeys.
1)
This bacterium is released in the feces of the
infected animal, thus when humans contract
this
disease it usually means that they have ingested
fecal material due to unsanitary
behavior.
c. In humans,
Salmonella can cause a severe
gastroenteritis.
d. The salmonella are hardy microbes that are
able to
survive outside their hosts in water, on moist surfaces etc.
for days to months
1) Safe food handling measures must be
stringently
followed.
2. DISEASE MECHANISM of Salmonella
a. Victims ingest the bacteria which invades the
intestinal
mucosa
setting up an infection that produces inflammation of
the
intestine resulting in diarrhea, fever, cramps, nausea,
abdominal
pain, and vomiting (GASTROENTERITIS).
b. The disease onset occurs within 8 to 48 hours
up to
several
days.
3. PROGNOSIS of Salmonella
a. The disease lasts 2 to 5 days to as long as
several
weeks.
4. TREATMENT of Salmonella
a. Fluid/electrolyte replacement
b. antibiotics are only used to counter
secondary infections.
5. PREVENTION of Salmonella
a. Cook poultry, ground beef, and eggs thoroughly before
eating.
b. Wash hands, kitchen work surfaces, and
utensils with hot
soapy water
immediately after they have been in contact
with foods
of animal origin.
c. Wash hands with soap after handling reptiles,
amphibians,
or birds, or after contact with pet feces.
1.
CAUSE - a gram positive, obligate anaerobic, spore-former that
is found in the gut of
many animals, including humans.
a. Besides producing a
FBD, it is responsible for producing
gas gangrene.
b. This disease is an INTOXICATION and
not an infection.
c. This FBD is usually the result of improper
storage of food
prepared in
advance.
d. A typical scenario goes something like this.
A holiday
turkey is
prepared, however during preparation the stuffing
gets contaminated
with C. perfringens spores (from poop)
left on the
turkey during their slaughter.
1) The stuffing is subsequently packed tightly
inside
the turkey. Because
stuffing is a excellent insulator,
it may not get hot enough
to kill the heat-resistant
spores.
2) At the first serving of the turkey no disease
occurs,
however once the stuffing,
containing the live spores
reaches room temperature
the spores germinate and
begin to grow rapidly
while producing toxins.
3) As the stuffing sits out for several hours
before
being stored in the
refrigerator in a large bowl,
bacterial growth continues
and since the large mass
of stuffing may take
several hours to cool down in the
refrigerator, growth continues
for several more hours.
4) When the "leftovers" are
eventually served they
contain toxic quantities
of bacterial products and the
eaters become ill.
2. DISEASE MECHANISM of C. perfringens
a. Contamination occurs via the fecal-oral route during
slaughtering
and food preparation.
b. The illness strikes within 8 to 16 hours and
produces
profuse
diarrhea.
3. PROGNOSIS of C. perfringens
a. Most victims recover in 1 to 4 days and no treatment is
usually
necessary except for the very young or the elderly.
4. PREVENTION of C. perfringens
a. Clostridium grows best between 45˚F and 140˚F.
Prepared
foods should be kept cooler or warmer than this.
b. Wash hands before preparing or serving foods.
c. When handling raw meat or poultry, consider
them
contaminated!
1) Wash your hands and any surfaces they have
touched before proceeding.
d. Be sure that meat,
poultry, and fish dishes are fully
cooked and don’t interrupt cooking to finish it later.
e. Don’t leave prepared
foods unrefrigerated for more than
two hours.
f. When foods are taken
from warming tables, they should
be refrigerated immediately, not left at room temperature to
cool.
g. Prepared foods should be
reheated to at least 165˚F
before serving.
F.
ESCHERICHIA
COLI 0157:H7
was
first recognized in 1982 during an
outbreak of a FBD in the state of
1. CAUSE of E.
coli 0157:H7 - E. coli
is a normal inhabitant of the
human and animal gut and
is the most studied bacterium on the
planet.
a. It is a gram negative, motile, plump,
non-spore-forming
rod.
b. The numbers 0157 and H7 refer respectively to
the
antigenic characteristics
of LPS (0157) and a flagella protein
(H7).
c. 0157:H7 contains a plasmid that
carries the gene for a
virulent toxin. Once the
infection is established, the toxin is
released, causing HEMMORRHAGIC
COLITIS and
HEMOLYTIC UREMIC SYNDROME.
d. The
bacteria resides in food (and water) that is
contaminated
with fecal material, usually from cattle,
although other sources may exist,
including humans.
e.
This bacterium has been cultured from raw milk, cheese,
turkey roll sandwiches, chicken, pork,
and raw vegetables;
and recently in unpasteurized fruit
juice.
f.
It has been spread between children at nursery schools
due to unsanitary conditions.
g.
2. DISEASE MECHANISM of E. coli 0157:H7
a. This bacterium enters its victims via the fecal-oral
route
and produces an infection in the victim's intestine.
b. The
onset of the disease occurs 24 to 72 hours after
ingestion.
c.
It varies from a mild gastroenteritis to a severe, often
deadly course described below.
d.
Hemmorrhagic colitis
results in damage of the intestine
accompanied by bleeding
and in severe cases destruction of
the intestine that can
only be stopped by surgical removal of
the infected tissue, often
several feet of it.
e. In hemolytic
uremic syndrome,(HUS), the kidney is
severely damaged and often
completely destroyed. Death
results from general organ
failure due to a combination of
the toxin effects and the
failure of crucial organs.
3. TREATMENT AND PROGNOSIS of E. coli 0157:H7
a. Antibiotics
seem to have little effect probably because
once tissue
damage sets in the blood supply is interrupted
which
prevents the drugs from reaching the infected sites.
b. Surgical removal of the infected tissue is
useful but very
traumatic
and it may not remove all the infection.
c. It appears to be more severe in small
children, possibly
because they
have not developed general low level immunity
to E.
coli.
4. PREVENTION of E. coli 0157:H7
a. The
bacterium is easily killed by heat, but if products like
hamburgers
are not heated so that all parts of the patty
reach a
lethal temperature, the organism can survive to
cause the
disease.
b. Drink only pasteurized milk and juice.
1. CAUSE – Discovered in
1972, Campylobacter jejuni is a
Gram-negative aerobic/microaerophilic,
motile helical bacteria
bacteria, now recognized as the leading bacterial diarrheal illness
in
the
a. Scientists now feel
they have evidence that suggests that
Campylobacter infections are the major cause of traveler’s
diarrhea.
1) The bacteria lives in the intestines of a
variety of
domestic animals
(chickens, cows, sheep, dogs, cats,
poultry etc.)
b. As its name implies this
disease usually hits a traveler 1
to 3 days after he/she has arrived in a foreign country and
consists of everything from a mild case of loose stools to a
full blown case of painful diarrhea where one is confined to
staying within 10 feet of a toilet until it passes.
c. A traveler may suffer
subsequent attacks as they visit
other countries or they may never suffer an attack.
2. DISEASE MECHANISM of traveler’s diarrhea
a. Transmission mostly through improper food
handling &
undercooking of meat,
milk, & by contact with infected
humans.
1) It is generally
spread by poor sanitation within the
home or institution, particularly via the kitchen.
b. The disease occurs 2-5
days after infection and lasts 7-
10 days.
c. It produces diarrhea,
fever, abdominal cramps, nausea,
vomiting, and bloody stools.
d. Visitors who eat the
local fecal-contaminated foods
and/or water can pick up unique, regional-strains, of this and
other foodborne disease.
1) As it reproduces in the visitor's intestine
it
produces slightly
different set of toxins to which the
new host reacts
unfavorably, as evidenced by their
developing a case
of the trots.
3 TREATMENT AND PROGNOSIS of traveler’s
diarrhea
a. It is generally self-limiting in healthy
patients, but is life-
threatening
in the infirmed.
1) The immunocompromised
elderly, particularly
those
in institutions like nursing homes, are especially
susceptible
to this organism.
b. The symptoms usually disappear within 1 to 3
days and it
is
treated with anti-diarrhea drugs.
c. Antibiotics are
effective in shortening the course of the
disease.
4. PREVENTION of traveler’s diarrhea
a. The high degree of contamination of poultry
with
Campylobacter, and other foodborne pathogens, requires
that
extra care be taken when preparing meals with poultry
on
the menu.
1) Your working assumption should be that "every
chicken and turkey" you buy is contaminated.
H. E.
COLI-INDUCED DIARRHEA
1. CAUSE - E. coli-induced diarrhea is a
major, if not the major
cause of death around the world
of young babies.
2. DISEASE
MECHANISM
a.
Usually the babies catch these organisms through
drinking contaminated water, often used to
make their
formula.
b. One of the unintended
consequences of introducing baby
formulas into underdeveloped countries is an increase in
infant death from diarrhea as the mother switch to formula
made with contaminated water from breast feeding.
IX. ORAL REHYDRATION
THERAPY – many of the deaths from waterborne
and foodborne diseases result from
dehydration and shock.
A. Prevention and treatment of dehydration is
critical.
1. If a victim can be given enough water
and electrolytes to replace
those
lost, they will usually recover spontaneously.
2.
In places where oral rehydration therapy has been vigorously
applied the fatalities from diarrhea
fell by as much as 50% and the
cost of treatment for diarrhea
declined by 75%.
B. Oral rehydration therapy consists of making
up the following solution in
one
liter:
1/2 teaspoon salt
1/4 teaspoon potassium or sodium
bicarbonate or citrate
1/4 teaspoon of potassium chloride
4 tablespoons of glucose, rice, wheat
or potato flour
C. A reasonable alternative formulation is Ricelyte or a sports-drink sold
as
a replacement drink for salts lost on hot days.
D. A word of warning here. BABIES die very
quickly from dehydration and
shock
and there is a myth in many societies that if a baby is vomiting it
should
not be given liquids because it hurts them to vomit. THIS IS A
SURE
WAY TO KILL THE BABY.
IX. THE PREVENTION OF FBD or MOMMIE WAS
RIGHT (AGAIN!)
A.
Basically the elimination of foodborne diseases requires rigorous
application of basic rules
of hygiene and sanitation that everyone learns in
kindergarten but
frequently fails to apply in everyday life. Your MOMMIE
told you all the following
and she was right:
1. Wash your hands after pooping, especially if
you're going to be
handling
food for yourself or anyone else.
2. Wash your hands after playing with the dog,
cat, ferret or alien,
especially
if you're going to be handling food for yourself or anyone
else.
3. Wash your hands after playing in the dirt,
especially if you're
going
to be handling food for yourself or anyone else.
4. Don't eat dirty or spoiled food (DUH!).
5. Don't eat off of dirty dishes or utensils
(double DUH!).
6. Develop and practice good KITCHEN HABITS,
including the
following
…
§
Prepare all fresh meat dishes in a separate area of the kitchen.
§
Do not use utensils used
to cut up meat on other foods, like salad makings; use separate
cutting boards for meat and vegetables; color coded ones help without washing
adequately in-between.
§
Wash the meat preparation area (counter- and stovetops) and
utensils with bleach or hot soapy water when finished.
§
Wash hands well between working with meat and vegetables by
scrubbing with soap for 30 seconds.
§
Cook all foods, especially meats, thoroughly until there is no
sign of redness in the center or
§
Always assume that fresh food is contaminated, no matter how clean
it looks or how well it is packaged and wash it thoroughly in hot, soapy water,
removing all dirt, feces (DUH) etc.
§
Never store food made with raw eggs (e.g. hollandaise sauce) at
room temperature.
§
Store all food that is prepared ahead of time in small batches in
the refrigerator.
§
Put away leftovers (like that turkey stuffing) immediately after
the meal in small portions that will cool quickly in the refrigerator.
§
Avoid unpasterurized milk and milk
products and juices.
§
In your shopping cart keep meats bagged and separate from
ready-to-eat foods; asked that meats be bagged separately at the checkout
stand..
§
Store meats separately from all other foods in the refrigerator.
§
When eating out don't order ground meat products (yeah, right!!)
and avoid salads (who am I kidding?).
§
Don't drink unchlorinated or any water
not treated to remove bacteria/viruses.
B. All of these suggestions add up to one thing:
AVOID EATING LIVE
FECAL MICROBES unless they are well
cooked!
C.
THE MICROWAVE ISSUE: The ubiquity
of the MICROWAVE in our
kitchens also has added a set of new
problems and concerns about the
microbial safety of our food supplies.
1. Microwaves work by heating up the WATER
molecules in the
food. This means that if
any portion of the food is dry, like potato
skin, it may not be heated
sufficiently to kill the pathogens residing
there.
2. Another problem with microwaves is the uneven
distribution of
the microwaves.
a. Not all parts of a food are heated equally
thus some
areas of the food fail to
reach the temperatures which are
lethal to pathogens in
those portions of the food.
3. Microwave instructions
inform the user that it is necessary to
allow "STAND TIME" so the heat from the heated portions
can
diffuse to the unheated areas; but the rushed nature of our busy
lives makes it difficult to follow these instructions.