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FOOD
MICROBIOLOGY
Judith Espinoza, MPH
Epidemiologist
City of Albuquerque
October 2008
Overview
Types of Pathogens
„ Basic Terminology
„ Common Microorganism Associated
with Foodborne Illness
„ Categories of Microorganisms by
„
„ Symptoms,
Possible Causes, Spore
Forms, Toxin Producers
Food Microbiology
Types of Pathogens
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Prions
Smallest
„ Protein
„ Known to cause variant CreutzfeldtCreutzfeldtJakob disease (vCJD
(vCJD)) (Mad Cow)
„ Long incubation
„
Food Microbiology
Viruses
„
„
„
„
Smaller than bacteria
No cell walls, membrane or nucleus
Can NOT reproduce outside a host
(Require a living cell to reproduce)
Can survive outside a host
Food Microbiology
Bacteria
„
„
Largest number of living organisms on
earth.
Forms –
„ round
(Staph
),
(Staph),
(Salmonella
),
(Salmonella),
„ spiral (Campylobacter
(Campylobacter))
„ comma shaped Vibrio
„ rod
„
„
Reproduce by binary fission
Many pathogenic bacteria are facultative
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Bacteria
„
„
All bacteria have vegetative state
(reproduce and generate waste)
Some form spores
„ Bacilli
(Bacillus
(Bacillus cereus)
cereus)
(Clostridium perfringens,
perfringens,
Clostridium botulinum)
botulinum)
„ Clostrida
„
SporeSpore-forming bacteria generally are
found in animal products or foods like
vegetables that are grown in the soil.
Food Microbiology
Molds
Mycology (Myco
=fungus)
(Myco=fungus)
„
„
„
„
„
Single celled or Multicellular
Wide pH range
Grow best in damp dark environments
Musty smell
Some produce mycotoxins
„ Aflatoxin
mold growing on nuts, corn,
wheat (found in peanut butter)
„
Some mold is beneficial
Food Microbiology
Yeast
(Part of Mycology and Fungi)
„
„
„
Single celled organisms that convert food
to alcohol and sugar by fermentation.
Need moisture, food in the form of sugar
or starch, and warmth.
Yeasts are responsible for few illnesses in
humans and there is no evidence that they
are transmitted by food.
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Parasites
„
„
„
Must live on or inside a living organism to
reproduce, can survive without a host
Usually bigger than bacteria and multimulticellular
FDA two methods for destroying parasites
in raw animal food products
„
„
Freezing
Cooking
Food Microbiology
Basic Terminology
Oxygen Requirement
Temperature Terms
Types of Toxin
Bacteria Growth
Foodborne Illness
Food Microbiology
Aerobe
An organism, especially a
bacterium, requiring oxygen to
live.
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Anaerobe
(An- before a word means without)
An organism, especially a bacterium,
NOT requiring oxygen to live.
Examples - Clostridium (botulism and canned
goods)
Food Microbiology
Facultative
Able to grow either with or
without the presence of free
oxygen.
Most foodborne disease-causing microorganisms
are facultative anaerobes
Food Microbiology
Microaerophilic
Aerobic Bacteria that grow
better under slightly reduced
oxygen requirements.
Example - Campylobacter
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•MesophileMesophile-a microoganism that grows
best at moderate temperatures with
optimum growth between 77˚
77˚ F and
113 ˚ F (25 ˚C -45 ˚C)
•Psychrophile -a microorganism
capable of growing at refrigerated or
room temperatures but grow best at
cold temperatures. Optimum 47 ˚ F -68
˚ F (5 ˚C -20 ˚C )
•Thermophile - a microorganism that
grows best at temperatures above 110
˚ F (43 ˚ FC)
Food Microbiology
Examples of toxins:
Some types of toxins can be used to
describe where they are produced in the
body or in the food.
„
„
Endotoxins – produced in the body
Exotoxins – produced in the food
Food Microbiology
Examples of toxins:
Some types of toxins can be used to
describe where in the body they affect.
„
„
EnterotoxinsEnterotoxins- affect the small intestine
Neurotoxins – affect the central nervous
system
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Examples of toxins:
Other types of toxins can describe what
type of organism produces it.
„
Mycotoxins – produced by molds
ShigaShiga-toxins – particular type of toxin
produced by bacteria E. coli & Shigella
Ciguatoxin – produced by algae
„
Scombrotoxin – histamine poisoning (fish)
„
„
Food Microbiology
Colony
A cluster of microorganisms that is
growing within, or on the surface
of a nutrient medium and that
contains millions of cells.
Food Microbiology
Binary Fission
The process by which bacteria
reproduce (nonsexual
reproduction) dividing in two under
ideal conditions
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Bacterial Growth
„
„
„
„
Lag – bacteria
exhibit little or no
growth
Log Bacteria growth
is very rapid
Stationary – number
of new bacteria =
the number dying
Decline – rapid die
off.
Stationary
25
20
15
Log
Decline
10
5
0
Lag
Food Microbiology
Infective Dose
The number of microorganisms
required to cause a foodborne
illness in one person
Shigella spp. as few as 10 cells depending on
age and condition of host.
Listeria monocytogenes is unknown, but in
susceptible persons, fewer than 1,000 total
organisms may cause disease.
Food Microbiology
Types of Foodborne
Illnesses
Three categories
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Infection -caused by eating food that
contains living diseasedisease-causing
microorganisms
Intoxication -caused by eating food
that contains a harmful chemical or
toxin produced by bacteria or other
source
ToxinToxin-Mediated Infection -caused by
eating food that contains harmful
microbes that will produce toxin once
inside the body.
Food Microbiology
Microorganisms
Some of the most common
organism that cause foodborne
illness
„ Bacteria
„Viruses
„Parasites
Food Microbiology
Gram positive or gram negative
refers to how bacteria appear under a
microscope after beginning stained.
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Common Foodborne
Pathogens by Gram Stain Type
„
Gram Positive
„ Bacillus cereus
„ Clostridium
perfringens
„ Clostridium
botulinum
„ Listeria
monocytogenes
„ Staphylococcus
aureus
„
Gram Negative
„ Campylobacter
jejuni
„ Shiga toxin –
producing E. coli
„ Salmonella spp.
spp.
„ Shigella spp.
spp.
„ Vibrio spp.
spp.
Food Microbiology
Bacillus cereus
„
Foodborne illness(es)
illness(es)
„ Intoxication
(vomiting {exotoxin
})
{exotoxin})
Infection (diarrhea
{enterotoxin})
enterotoxin})
„ ToxinToxin-Mediated
„
„
„
Gram Positive rod (soil bacteria)
Spore former (spores heat resistant)
Facultative
Food Microbiology
Clostridium perfringens
„
„
„
„
Food borne illness – toxintoxin-mediated
infection (diarrhea {enterotoxin
})
{enterotoxin})
Anaerobes (require very little oxygen)
Usually due to improperly cooling food so
that spores are able to return to vegetative
state.
Also causes gangrene in wound or skin
infections unrelated to food.
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Clostridium botulinum
•Food borne illness – intoxication –
symptoms are neurological and is one of
the deadliest biological toxins known to
man (dizziness, double vision, trouble
breathing . . .){neurotoxin}
•Anaerobes (require very little oxygen)
•Usually due to improperly cooling food
so that spores are able to return to
vegetative state.
Food Microbiology
Campylobacter jejuni
„
Foodborne illness
„ infectioninfection- an invasive organism.
„ toxintoxin-mediated
infection - pathogenic
mechanisms are still not completely
understood, but it does produce a heatheat-labile
toxin that may cause diarrhea.
„
Causes very watery diarrhea and/or bloody
diarrhea
Food Microbiology
Campylobacter jejuni
„
„
„
Gram negative curvy rod
Found in many of the same foods & has
some of the same symptoms as
Salmonella but is microaerophilic and
had a different onset time (2(2-5 days) .
Relatively fragilefragile- sensitive to environmental
stresses (e.g., 21% oxygen, drying, heating,
disinfectants, acidic conditions)
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Shiga toxin-producing
Eschericha coli
Foodborne illness
„
„
„
Infection
ToxinToxin-mediated infection (watery diarrhea –
bloody stools) {enterotoxin
{enterotoxin}}
Gram negative rod
E. coli – normal flora in most mammals
(humans, cattle, dogs, cats, goats) but not
all are pathogens and not all types
produce toxins.
„
„
Food Microbiology
Listeria monocytogenes, spp
„Foodborne
illness – infection
monocytogenes may invade
the gastrointestinal epithelium.
„Can cause miscarriages
„The overall mortality for meningitis
may be as high as 70%; from
septicemia 50%, from
perinatal/neonatal
perinatal/neonatal infections greater
than 80%.
„In infections during pregnancy, the
mother usually survives.
„L.
Food Microbiology
Listeria monocytogenes, spp
„
„
„
„
L. monocytogenes is quite hardy and
resists to freezing, drying, and heat.
Does not form spores
Can grow slowly in cold temperatures and
can survive in highhigh-salt food.
Foods – raw dairy products (also cold
cuts)
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Salmonella spp.
„
„
„
„
Foodborne illness – mostly infection
Similar in many ways to Campy.
Very larger group of bacteria
Cause of disease -- Penetration and
passage of Salmonella organisms from gut
lumen into epithelium of small intestine
where inflammation occurs; there is
evidence that an enterotoxin may be
produced.
Food Microbiology
Shigella spp.
spp.
„
Foodborne illness
„ Infection
„ ToxinToxin-mediated infection
„
The disease is caused when virulent Shigella
organisms attach to, and penetrate, epithelial
cells of the intestinal mucosa. After invasion,
they multiply intracellularly,
intracellularly, and spread to
contiguous epitheleal cells resulting in tissue
destruction. Some strains produce
enterotoxin (a Shiga toxin very much like the
E. coli).
coli).
„
Poor hygiene practices
Food Microbiology
Staphylococcus aureus,
„
„
„
„
„
Gram positive cocci
One type of foodborne illness –
intoxication (vomiting)
Found in ready to eat food or prepre-cooked
food that are reheated.
Exotoxin – very heat stable
Very common skin bacteria
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Vibrio spp
„
„
„
„
Foodborne illness
„ infectioninfection„ ToxinToxin-mediated infection - caused by
ingesting the organisms, which attach to
the small intestine and produce cholera
toxin (enterotoxin)
enterotoxin)
Most commonly associated with water or
food from the water.
Gram negative straight or curvy rod
Can cause very watery diarrhea
Food Microbiology
Viruses
Hepatitis A, Norwalk virus,
Rotavirus,
Food Microbiology
Hepatitis A,
„Poor
hygiene & raw seafood
„Jaundice (liver infection)
„Long incubation period (10(10-50
days without showing symptoms)
„Foods have been implicated in
over 30 outbreaks since 1983 ,
seafood, lettuce , frozen
strawberries
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Norwalk virus
„
„
„
„
„
Quick onset 22-3 days
Contaminated water
Ingestion of raw or insufficiently steamed
clams and oysters poses a high risk.
Other foods contaminated by ill food
handlers.
Ten well documented outbreaks caused
by Norwalk virus were reported in the
U.S., involving a variety of foods: fruits,
salads, eggs, clams, and bakery items.
Food Microbiology
Rotavirus
„
„
„
„
Quick onset 11-3 days
Symptoms often start with vomiting
followed by 44-8 days of diarrhea.
Temporary lactose intolerance may occur.
Contaminated water or PersonPerson-toto-person
The virus has not been isolated from any
food associated with an outbreak, and no
satisfactory method is available for routine
analysis of food.
Food Microbiology
Parasites
Anisakis spp.,
spp., Cycolspora
cayetanensis,
cayetanensis, Cryptosporidium parvum
Giardia lamblia,
lamblia, Toxoplasma gondii,
gondii,
Trichinella spiralis
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Anisakis spp.
„
„
„
„
Unsure onset 1 hr – 2 weeks
Frequently diagnosed when the affected
individual feels a tingling or tickling
sensation in the throat and coughs up or
manually extracts a nematode
Fewer than 10 cases are diagnosed in the
U.S. annually. However, it is suspected
that many other cases go undetected.
The disease is transmitted by raw,
undercooked or insufficiently frozen fish
and shellfish, and its incidence is expected
to increase with the increasing popularity
Food Microbiology
of sushi and sashimi bars.
Cycolspora cayetanensis
„
„
„
„
„
~ 1 week onset
Water, berries, raw vegetables
Act upon the small intestine resulting in
water diarrhea (explosive)
PersonPerson-toto-person, oral fecal route
Currently little is known about this
organism, although cases of
cyclosporiasis are being reported from
various countries with increasing
frequency.
Food Microbiology
Cryptosporidium parvum
„
„
„
1 week
Contaminated water
Small and resistant to chlorine,the
sporocysts are resistant to most chemical
disinfectants, but are susceptible to drying
and the ultraviolet portion of sunlight.
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Giardia lamblia
„
„
„
„
„
Last 1 to 2 weeks, but some chronic
infections last months to years.
Contaminated water
Bigger than crypto
Infectious Dose - Ingestion of one or more
cysts may cause disease.
Five outbreaks have been traced to food
contamination by infected food handlers,
and the possibility of infections from
contaminated vegetables that are eaten
raw cannot be excluded.
Food Microbiology
Toxoplasma gondii
„
„
Toxoplasmosis is considered to be the
third leading cause of death attributed to
foodborne illness in the United States.
Women newly infected with Toxoplasma
during pregnancy and anyone with a
compromised immune system should be
aware that toxoplasmosis can have severe
consequences for them.
Food Microbiology
Toxoplasma gondii
„
„
A parasite that causes a very severe
disease that can cause central nervous
system disorders, such as mental
retardation and visual impairment in
children.
Sources: Raw or undercooked pork,
lamb, or venison and cat, rat, rodent, or
bird feces.
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Trichinella spiralis
„
„
„
„
Trichinellosis is caused by a parasite that is a
nematodes (roundworms).
Rats and rodents are reservoir
Carnivorous/omnivorous animals, such as pigs
or bears, feed on infected rodents or meat from
other animals.
Humans are accidentally infected when eating
improperly processed meat of these carnivorous
animals (or eating food contaminated with such
meat).
Food Microbiology
Specific Toxin
Aflatoxin,
Aflatoxin, Ciguatoxin,
Ciguatoxin,
Scombrotoxin
Food Microbiology
Aflatoxin
„
„
„
„
Intoxication –acute or chronic
Hepatocarcinogen (Hepato = liver,
Carcingoen=
Carcingoen= cancer causing)
Produced by fungi (mold) exotoxin
In the United States, aflatoxins have been
identified in corn and corn products,
peanuts and peanut products, cottonseed,
milk, and tree nuts such as Brazil nuts,
pecans, pistachio nuts, and walnuts.
Food Microbiology
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Ciguatoxin
„
„
„
Produced by algae
Caused by the consumption of subtropical
and tropical marine finfish which have
accumulated naturally occurring toxins
through their diet.
The relative frequency of ciguatera fish
poisoning in the United States is not
known.
Food Microbiology
Ciguatoxin
„
„
Initial signs of poisoning occur within six
hours after consumption of toxic fish and
include perioral numbness and tingling
(paresthesia),
paresthesia), which may spread to the
extremities, nausea, vomiting, and
diarrhea.
Ciguatera poisoning is usually selfself-limiting,
and signs of poisoning often subside
within several days from onset.
Food Microbiology
Scombrotoxin
(also called Histamine Poisoning)
„
„
„
Caused by the ingestion of foods that
contain high levels of histamine.
histamine.
Histamine and other amines are formed by
certain bacteria during production - such
as Swiss cheese, or by spoilage of foods
such as fishery products, particularly tuna
or mahi mahi.
mahi.
Neither cooking, canning, or freezing
reduces the toxic effect.
Food Microbiology
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Categories
Characteristics
Symptoms,
Possible Sources
Spore Formers
Toxin Producers
Food Microbiology
The two anaerobic bacteria
„ Clostridium
perfringens
„ Clostridium botulinum
Food Microbiology
The bacteria that produce
toxin in the food (exotoxin)
„ B.
cereus
„ C. botulinum – only neurotoxin
„ Staph.
Staph. aureus
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Poor Hygiene
All the viruses – Hep A, Noro and
Roto
„ Shigella spp.
spp.
„ Staph.
Staph. aureus
„ Vibrio spp
„ E. coli
„ Salmonella spp.
spp.
„
Food Microbiology
Contaminated water
All the viruses – Hep A, Noro and
Roto
„ Some parasites – Cyclospora,
Cyclospora,
Cryptosporidium, Giardia
„ Vibrio spp
„
Food Microbiology
The bacteria that are most
likely to produce bloody
diarrhea
„ Campylobacter
„ Shiga
toxin producing E. coli
„ Shigella
Food Microbiology
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Which bacteria can produce
spores?
„
„
„
B. cereus
Clostridium perfringens
Clostridium botulinum
Food Microbiology
Summary
„
Categories of Microorganisms by
„ Symptoms,
Possible Causes, Spore
Forms, Toxin Producers
Common Microorganism Associated
with Foodborne Illness
„ Basic Terminology
„ Types of Pathogens
„
Food Microbiology
References
„
„
„
„
„
Modern Food Microbiology,
Microbiology, 6th edition, 2000
James M. Jay
http://www.microbeworld.org/microbes/virus/
http://www.doctorfungus.org/mycoses/index.h
tm
http://www.foodsafety.gov/~mow/intro.html
http://www.microbionet.com.au/salmonella.ht
http://www.microbionet.com.au/salmonella.ht
m
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