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The nature of microorganismsThe nature of microorganismsand parasitesand parasites

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pathogenic organisms

spoilage organisms

useful organisms

Microorganisms classifiedMicroorganisms classifiedby their significanceby their significance

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Dangerous microorganismsDangerous microorganismsand parasitesand parasites

Foodborne diseases

bacteria

moulds

viruses

parasites

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Major bacteria causing Major bacteria causing foodborne diseasefoodborne disease

Aeromonas spp.

Bacillus cereus

Brucella spp.

Campylobacter jejuni

Clostridium botulinum

Clostridium perfringens

Escherichia coli

Listeria monocytogenes

Mycobacterium bovis

Salmonella spp.

Shigella spp.

Staphylococcus aureus

Vibrio cholerae

Vibrio parahaemolyticus

Vibrio vulnificus

Yersinia enterocolitica

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Spoilage microorganismsSpoilage microorganisms

bacteria

yeasts

moulds

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Food products madeFood products madewith useful microorganismswith useful microorganisms

fermented meats yoghurt cheese beer leavened bread soy sauce fermented soybean (tofu)

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Useful microorganismsUseful microorganisms

Lactic acid bacteria (LAB) These ferment carbohydrates into organic acids which inhibit

Salmonella Staphylococcus Listeria Clostridium E. coli

LAB are found in Plants Soil Animals Human Gut

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World population is

5.9 BILLION

i.e. 5 900 000 000

1 cup

of yoghurt contains

20 X this number!

i.e. 120 000 000 000

separate living

organisms.

Microorganisms are very smallMicroorganisms are very small

YOGHURT

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Bacterial divisionBacterial division

1

2

3

4

5

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Bacterial growth curveBacterial growth curve

Toxic

+_

+ +_ _ _ _ _ _ _ _ _ __ _ _ _ _ _

- - - - - - - - - - - -+++++++++++

Time to spoilage

Spoils

Time0

1

2

3

4

5

6

7

8

9

Lag phase Log phase Stationary phase

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lag phase(short) period of adjustment to environment

logarithmic growth phasegrowth begins and accelerates to a phase of rapid, constant exponential growth

stationary phasedepletion of nutrients and accumulation of toxic metabolic products growth is slowed to a point where cell division and cell death are in balance

death phasepopulation decreases due to death of cells

Phases of bacterial growthPhases of bacterial growth

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Some toxigenic mouldsSome toxigenic mouldscausing foodborne diseasecausing foodborne disease

Aspergillus spp.

Fusarium spp.

Penicillium spp.

( Main sources - fruits, nuts and grains )

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Major virusesMajor virusescausing foodborne diseasecausing foodborne disease Hepatitis A and E viruses

Small Round Structured Viruses (e.g. Norwalk agent)

Rotavirus

Polio virus

-Viruses, unlike bacteria, cannot be cultivated outside a living host. -They are much smaller and can be seen only with an electronmicroscope.

- There are no animal or plantborne viruses causing foodborne illness. All foodborne viruses originate from the human gut, and use it as their target

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Virus structureVirus structureProtein Capsule

Nucleic acid(DNA or RNA)

Poliovirus

Hepatitis-A virus

RotavirusNorwalk-like or

SRSV

Viruses consist of a protein capsule which may be surrounded by a lipid/protein envelope. Inside there is DNA or RNA, a polymerase and sometimes other specific enzymes associated with the replication of the virus.

Viruses cannot replicate outside a host cell. They attach to the host cell where the viral DNA or RNA, and other enzymes enter. Signals are sent that cause the host cell’s replicative apparatus to be used for the replication of the virus.

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Rotavirus Poliovirus Hepatitis A& E virus

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Virus levels required forVirus levels required forinfection and detectioninfection and detection

infection10 -100 particles / ml

detection (finding)105 - 106 particles / g(by electron microscopy)

104 - 105 particles / g(by radioimmunoassay)

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Examples of peak excretion periodExamples of peak excretion periodof some faecal virusesof some faecal viruses

SRSV 1 - 3 days

Astrovirus 1 - 4 days

Rotavirus 1 - 7 days

Adenovirus prolonged

Coronavirus prolonged

Hepatitis A virus pre-jaundice

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Coronavirus (respiratory & gastrointestinal tract)

• Astrovirus (Diarrhea) Adenovirus (respiratory infections & diarrhea)

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The human intestines - the sourceThe human intestines - the sourceand target of foodborne virusesand target of foodborne viruses

cause diarrhoea Small round structured viruses (SRSV) Astrovirus Adenovirus Coronavirus Rotavirus

do not cause diarrhoea Hepatitis A virus Poliovirus Echovirus (found in gastrointestinal tract) Coxsackievirus (flaccid paralysis & spastic paralysis)

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Major parasitesMajor parasitescausing foodborne diseasecausing foodborne disease

• Cryptosporidium

• Entamoeba histolytica

• Giardia

• Toxoplasma

• Fasciola

• Fasciolopsis

• Haplorchis

• Opisthorchis

• Paragonimus

• Cysticercus cellulosae

Protozoa

Helmints (ព្�ន)

• Angiostrongylus• Anisakis• Ascaris• Capillaria• Gnathostoma• Trichinella

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Transmission of trichinellosisTransmission of trichinellosis ( (ដង្កូ��វដង្កូ��វ))

Infected person

encystedlarvae

in muscle

Adults inintestine

encystedlarvae

in muscle

PIG

Adults inintestine

Adults in intestine

encysted larvaein muscle

RAT

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Transmission of cysticercosisTransmission of cysticercosis (worm)(worm)

Infected person

Taenia saginata

Taenia solium

Adult in intestine

Eggs in soil

Contaminated vegetable, water

Regurgitating

Cysticercus cellulosaein the body

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Transmission of toxoplasmosisTransmission of toxoplasmosis

Infected person

Transplacenta transmission

Cat

OocystBradyzoitein meat

MammalsBirds

(Cattle, piggoat etc.)

Meat

ingestion

handling

meatBaby

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Transmission of anisakiasisTransmission of anisakiasis

Infected person

Adult

3rd stage larvae

Fishencysted larvae

inMarine mammals

inkrill

Acute abdominal pain

2nd stage larvae

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Transmission of ascariasisTransmission of ascariasis

Infected person

Adult worms in intestine

Contaminated vegetables

with night soil

Infective eggs

Unsegmented eggs excreted

Contaminatedhand

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Transmission of fascioliasisTransmission of fascioliasis

Infected personSheep

SnailAquatic plantsAdults in bile duct

Juvenile migrate to other organs ie. brain, eye, muscle

cercariaencystedmetacercaria

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TransmissionTransmission of giardiasis of giardiasis

Infected person Giardia cysts in intestine

Transfer to mouth

Cysts on handsCyst

Cyst in water

Water used to washfruit and vegetables

Drinking water

Giardia lamblia excreted

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Transmission of Transmission of cryptosporidiumcryptosporidium

The Environment

Effluents, slurry & sludgedumped on land

Liquid discharges and effluents dumped in water

Food chain

Recreational use of land and water

Water treatment system

Indigenouswildlife

FarmAnimals

Pets

Human

Importedexotic

livestock

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Nature of bacteria, moulds, virusesNature of bacteria, moulds, virusesand parasites - Key messages and parasites - Key messages (1)(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 andmay produce toxins

understanding the factors controlling growthof microorganisms allows us to control themin food

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bacteria may be harmful or useful

bacteria, yeasts and moulds can be usedto preserve foods

lactic acid bacteria secrete lactic and other organic acids

organic acids inhibit pathogens in food andin the gut

viruses and parasites do not grow in food

Nature of bacteria, moulds, virusesNature of bacteria, moulds, virusesand parasites - Key messages (2)and parasites - Key messages (2)