The nature of microorganisms
and parasites
FS0102 1
2000
Microorganisms classified
by their significance
pathogenic organisms
spoilage organisms
useful organisms
FS0102 2
2000
Dangerous microorganisms
and parasites
Foodborne diseases
FS0102 3
2000
‹
bacteria
‹
moulds
‹
viruses
‹
parasites
Major bacteria causing
foodborne disease
Aeromonas spp.
Mycobacterium bovis
Bacillus cereus
Salmonella spp.
Brucella spp.
Shigella spp.
Campylobacter jejuni
Staphylococcus aureus
Clostridium botulinum
Vibrio cholerae
Clostridium perfringens
Vibrio parahaemolyticus
Escherichia coli
Vibrio vulnificus
Listeria monocytogenes
Yersinia enterocolitica
FS0102 4
2000
Spoilage microorganisms
bacteria
Yeasts
moulds
FS0102 5
2000
Food products made
with useful microorganisms
fermented meats
yoghurt
Cheese
beer
leavened bread
soy sauce
fermented soybean (tofu)
FS0102 6
2000
Useful microorganisms
Lactic acid bacteria (LAB)
These ferment carbohydrates into organic acids
which inhibit
‹
‹
‹
‹
‹
Salmonella
Staphylococcus
Listeria
Clostridium
E. coli
LAB are found in
‹
‹
‹
‹
FS0102 7
2000
Plants
Soil
Animals
Human Gut
Microorganisms are very small
YOGHURT
1 cup
of yoghurt contains
20 X this number!
World population is
5.9 BILLION
i.e. 5 900 000 000
FS0102 8
2000
i.e. 120
000 000 000
separate living
organisms.
Microorganisms are very small
Cell wall
Ribosomes
FS0102 9
2000
Cytoplasmic
membrane
Nuclear
body
Cytoplasm
Bacterial division
1
2
3
4
5
FS0102 10
2000
Bacterial growth curve
Toxic
- - - - - - - - - - - -+++++++++++
Spoils
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
9
8
7
6
5
4
3
+ + +
Time to spoilage
2
1
0
Time
Lag phase
FS0102 11
2000
Log phase
Stationary phase
Phases of bacterial growth
lag phase
(short) period of adjustment to environment
logarithmic growth phase
growth begins and accelerates to a phase of
rapid, constant exponential growth
stationary phase
depletion of nutrients and accumulation of toxic
metabolic products growth is slowed to a point
where cell division and cell death are in
balance
death phase
population decreases due to death of cells
FS0102 12
2000
Some toxigenic moulds
causing foodborne disease
Aspergillus spp.
Fusarium spp.
Penicillium spp.
( Main sources - fruits, nuts and grains )
FS0102 13
2000
Major viruses
causing foodborne disease
Hepatitis A and E viruses
Small Round Structured Viruses
(e.g. Norwalk agent)
Rotavirus
Polio virus
FS0102 14
2000
Virus structure
Protein Capsule
Poliovirus
Hepatitis-A virus
Rotavirus
Norwalk-like or
SRSV
Nucleic acid
(DNA or RNA)
FS0102 15
2000
Virus levels required for
infection and detection
infection
10 -100 particles / ml
detection
105 - 106 particles / g
(by electron microscopy)
104 - 105 particles / g
(by radioimmunoassay)
FS0102 16
2000
Examples of peak excretion period
of some faecal viruses
FS0102 17
2000
SRSV
1 - 3 days
Astrovirus
1 - 4 days
Rotavirus
1 - 7 days
Adenovirus
prolonged
Coronavirus
prolonged
Hepatitis A virus
pre-jaundice
The human intestines - the source
and target of foodborne viruses
cause diarrhoea
‹
‹
‹
‹
‹
Small round structured viruses (SRSV)
Astrovirus
Adenovirus
Coronavirus
Rotavirus
do not cause diarrhoea
‹
‹
‹
‹
FS0102 18 2000
Hepatitis A virus
Poliovirus
Echovirus
Coxsackievirus
Major parasites
causing foodborne disease
Protozoa
• Cryptosporidium
• Entamoeba histolytica
• Giardia
• Toxoplasma
Helmints
• Angiostrongylus
• Fasciola
• Anisakis
• Fasciolopsis
• Ascaris
• Haplorchis
• Opisthorchis
• Paragonimus
• Capillaria
• Gnathostoma
• Trichinella
FS0102 19 2000
• Cysticercus cellulosae
Transmission of trichinellosis
Infected person
Adults in
intestine
encysted
larvae
in muscle
Adults in
intestine
RAT
PIG
encysted
larvae
in muscle
FS0102 20
2000
Adults in
intestine
encysted larvae
in muscle
Transmission of cysticercosis
Infected person
Cysticercus cellulosae
in the body
Taenia saginata
Regurgitating
Taenia solium
Contaminated
vegetable, water
Adult in intestine
Eggs in soil
FS0102 21
2000
Transmission of toxoplasmosis
Cat
Infected person
Bradyzoite
in meat
Oocyst
ingestion
Transplacenta
transmission
Baby
FS0102 22 2000
Mammals
Birds
(Cattle, pig
goat etc.)
handling
meat
Transmission of anisakiasis
Infected person
Adult
in
Marine mammals
Fish
encysted larvae
3rd stage larvae
in
krill
Acute abdominal pain
FS0102 23
2000
2nd stage larvae
Transmission of ascariasis
Infected person
Adult worms
in intestine
Contaminated
hand
Contaminated
vegetables
with night soil
Unsegmented
eggs excreted
FS0102 24
2000
Infective
eggs
Transmission of fascioliasis
Infected person
Adults in
bile duct
Sheep
Aquatic plants
encysted
metacercaria
Juvenile migrate
to other organs ie.
brain, eye, muscle
FS0102 25 2000
Snail
cercaria
Transmission of giardiasis
Giardia cysts in intestine
Infected person
Water used to wash
fruit and vegetables
Drinking water
Transfer to mouth
Giardia lamblia excreted
Cyst in water
Cysts on hands
Cyst
FS0102 26
2000
Transmission of cryptosporidium
The Environment
Effluents, slurry & sludge
dumped on land
Liquid discharges and
effluents dumped in water
Recreational use of
land and water
Food
chain
Water treatment
system
Farm
Animals
Indigenous
wildlife
FS0102 27 2000
Human
Imported
exotic
livestock
Pets
Nature of bacteria, moulds, viruses
and parasites - Key messages (1)
foodborne diseases are caused by bacteria,
moulds, viruses, and parasites
certain microorganisms are of greater
significance than others for humans
bacteria and moulds multiply on foods and
may produce toxins
understanding the factors controlling growth
of microorganisms allows us to control them
in food
FS0102 28
2000
Nature of bacteria, moulds, viruses
and parasites - Key messages (2)
bacteria may be harmful or useful
bacteria, yeasts and moulds can be used
to preserve foods
lactic acid bacteria secrete lactic and other
organic acids
organic acids inhibit pathogens in food and
in the gut
viruses and parasites do not grow in food
FS0102 29
2000