Industrial Lecture 8

8/4/2019 Industrial Lecture 8

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BIO 425

Industrial Microbiology

Lecture 8

Pathogenic microorganisms in foodindustry


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Content outline

Foodborne intoxications

Exotoxins Serotypes ofE.coli


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Foodborne intoxications

occurs when a person gets sick by eating

food:

that has been contaminated with an

unwanted m/o or toxin.

Often called food poisoning.


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Most common symptoms of

foodborne illnesses

Stomach cramps

Nausea

Vomiting

Diarrhoea

Fever


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Causes of food poisoning

inadequate control of temperature during

cooking, cooling and storage,

poor personnel hygiene,

cross-contamination of raw and processed

products,

inadequate monitoring of processes.


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Members of normal intestinal flora

Bacteroides spp. (B.fragilis), G(-) non-spore

former rods-dominant m/o

produce volatile & non-volatile fatty acids,

acetic, succinic, lactic etc.

Bifidobacterium spp. (B.bifidum) - G(+)

non-spore former rods

produce acetic & lactic acids


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Members of normal intestinal flora-2

Clostridium spp.(C.innocuum)-G(+) sporeforming rods.

Enterococcus spp.(E. faecalis) G(+) cocci,aerotolerant.

Eubacterium spp.-G(+) non-spore forming

rods, produce butyric, formic & aceticacids.

Fusobacterium spp. G(-) non-spore formingrods, produce N-butyric acid.


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Members of normal intestinal flora-3

Peptostreptococcus spp., G(+) cocci,

degrade peptone & amino acids.

Ruminococcus spp., G(+) cocci, produce

acetic, succinic and lactic acids, ethanol,

CO2 & H2 from CH4.


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Other genera of organisms present:

A minimum of 400 species,

includes:

Lactobacillus spp.

Proteus spp.

Klebsiella spp. E.coli spp.


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Pathogenic strains involved in major

outbreaks of food poisoning:

E.coli

G(-),

Catalase(+),

Oxidase(-),

facultatively anaerobic short rods. members of the familyEnterobacteriaceae.


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More about E.coli

Most isolates ferment lactose,

majority ofE.coli serotypes: not pathogenic

are part of the normal intestinal flora, about106 organisms / g.

used as an indicator:

as one of the coliforms to indicate faecalpollution of water,

raw ingredients and foods.


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Non-pathogenicE.coli colonize the infant gastrointestinal tract

within a few hours after birth,

its presence suppresses the growth of

harmful bacteria;

important for synthesizing appreciable

amounts of B-vitamins.


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Toxic strains ofE.coli

Three major types:

Exotoxins,

Enterotoxins,

Endotoxins.


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Exotoxins ofE.coli

Same as the bacterial protein toxins,

also called secreted toxins;

exert their biological activity (often lethal) in

minute doses.

extracellular,

excretory, heat-labile,

antigenic.


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Exotoxins ofE.coli

Exotoxins which result in extremely waterydiarrhoea:

act as:

directly on gut tissue, causing biochemical and /orstructural lesions which lead to diarrhoea.

causing specific action (e.g. net fluid loss) in thegut.

elevate cAMP levels, causing ion-flux changesand excess fluid secretion.


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Enterotoxins ofE.coli

Two types:

Cytotonic enterotoxins,

Cytotoxic enterotoxins.


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Cytotonic enterotoxins

E.g. Cholera toxin

Induce net fluid secretion:

by interfering with biochemical regulatory

mechanisms;

without causing overt histological damage.


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Cytotoxic enterotoxins

Induce actual damage to intestinal cells as a

necessary prelude to onset of net fluid secretion;

can be protein or lipopolysaccharide; invasive, kill target cells.

Mode of action: intracellular or by formation of

pores within cells.

Result: inflammatory diarrhoea which often

contains blood and leucocytes.


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Endotoxins ofE.coli Heat-stable, cell associated,

complex lipopolysaccharide (LPS)

structure;

Lipid A: Part of LPS which is responsible

for toxicity.

cause toxic shock, inflammation and fever.


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Cytolethal distending toxins (

CLD

T)

Affect host cell cycle regulation,

found in a variety of unrelated organisms.

Campylobacter jejuni

E.coli

Shigella dysenteriae Haemophilus ducreyi

Actinobacillus actinomycetemcomitans


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CLD

T)

Blocks cells in G2phase:

inhibits the dephosphorylation of the protein

kinase cdc2;

and this prevents entering into mitosis.

Belongs to a variety of exotoxin family.


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CLD

T)

Exotoxins:

If they attack a specific organ, they are

named as;

Neurotoxins,

Leukotoxin;

Hepatotoxin;

Cardiotoxin;


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Specific examples for exotoxins: Cholera toxin by Vibrio cholerae

Shiga toxin by Shigella spp.

cause bacterial dysentery.

Shiga toxin:E.coli O 157: H7

called also verotoxin, as it affectsmammalian Vero cell culture line.


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Groups of exotoxins Act at the cell membrane, type I,E.coli

stable toxin, B.cereus emetic toxin.

attack the membrane: type II;

Listeriolysin O (Listeria monocytogenes)

Perfringolysin O (Clostridium perfringens)

Cereolysin O (B.cereus)

E.coli heat labile toxin & shiga toxin.


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Groups of exotoxins

Penetrate the membrane to act inside the cell: type

III.

e.g. Botulinum toxins type A-F & tetanus toxin,cholera.

directly transported from the bacterium into the

target eucaryotic cell by type III secretion.

e.g. Toxins of Salmonella, Shigella & Yersinia.


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Campylobacter jejuni &

C.coli

Colonises the distal ileum and colon of the

human intestinal tract;

after colonizing the mucus;

and adhering to intestinal surfaces.


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C.coli

The organisms perturb the normal

absorptive capacity of the intestine;

by damaging epithelial cell function;

by cell invasion & production of heat labile

enterotoxin & cytotoxin,

and cytoskeletal altering toxin.


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C.coli

can easily cross-contaminate processed

food.

A contaminated piece of raw meat can leave

10000 Campylobactercells per cm2 on a

work surface.

G(-), thin rod, microaerophilic.

42-43 C-optimum T.


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C.coli

Symptoms:

Flu-like illness,

abdominal pain,

fever,

diarrhea.


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C.coli

Potential for spreading the infection:

Water,

milk,

meat,

poultry.


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Salmonella Member ofEnterobacteriaceae,

G(-),

facultatively anaerobic,

non-spore former,

Motile with peritrichious flagella-flagellainserted at many places around the cell

surface.


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Salmonella Over 2324 strains are defined.

Symptoms of food poisoning:

Diarrhoea,

nausea,

abdominal pain mild fever and chills

sometimes vomiting and headache.


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Major species ofSalmonella Salmonella typhimurium

Salmonella enteritidis

Salmonella paratyphii

Salmonella typhii


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Major sources ofSalmonella Raw meat,

Poultry,

Milk & dairy products,

Fish,

Shrimp, Sauces,

Salad dressings.


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PathogenicE.coli

EnterotoxigenicE.coli (ETEC):

common cause of travellers diarrhoea.

watery diarrhoea, rice-water like:

low grade fever,

colonizes the proximal small intestine.


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EnteropathogenicE.coli (EPEC)

Cause watery diarrhoea of infants,

no blood,

colonizes the microvilli over the entire

intestine.


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EnterohaemorrhagicE.coli (EHEC)

cause bloody diarrhoea,

cause haemorrhagic colitis,

cause haemolytic uremic syndrome(HUS),

cause thrombotic thrombocytopenic

purpurea (TTP).


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EnterohaemorrhagicE.coli (EHEC)

Includes the verotoxigenicE.coli (VTEC):

also known as shiga-toxin producingE.coli(or STEC) serotypes 0157, 026 and 0111.


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EnteroaggregativeE.coli (EAggEC)

Cause persistent watery diarrhoea;

especially in children, lasting more than 14

days.

produce a heat labile toxin, antigenically

related to haemolysin,

but not haemolytic and a plasmid-encoded

heat stable toxin (EAST1), unrelated to the

heat stable enterotoxin of ETEC.


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EnteroaggregativeE.coli (EAggEC)

Adhere to the intestinal mucosa and

elaborate the enterotoxins and cytotoxins,

which result in secretory diarrhoea and

mucosal damage.


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EnteroinvasiveE.coli (EIEC

) Cause fever and diarrhoea,

containing mucus and blood.

colonizes in the colon and carries a 120-140

mDa plasmid(Invasiveness plasmid),

carrying all the genes necessary for

virulence.


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Most important one fromE.coli EnterohaemorrhagicE.coli (EHEC);

E.coli O157: H7 with common outbreaks;

O157 and H7 refers to the serotyping of the

strains O and H antigens, respectively.


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E.coli O157: H7 Differs from the majority ofE.coli strains

that it does not grow,

or grows poorly at 44 C. and does not ferment sorbitol or produce -

glucuronidase.

cause severe damage to the lining of theintestine by verotoxin (VT) & shigatoxin(ST).


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Thrombotic thrombocytopenic

purpurea(TT

P) Blood platelets surround internal organs

leading to:

kidney damage,

and central nervous system damage.


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Thrombotic thrombocytopenic

purpurea(TTP) The most vulnerable of the population-

children and the elderly

develop haemorrhagic colitis (HC);

which may lead to haemolytic uraemic

syndrome (HUS).


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Haemorrhagic colitis (HC

) Less severe form of E.coli O157:H7

infection than HUS.

associated with:

sudden onset of severe crampy abdominal

pains.

non-bloody (watery) diarrhoea,

vomiting.


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Haemolytic Uremic

Syndrome(HUS) Patient suffers from bloody diarrhoea;

haemolytic anemia;

kidney disorder;

renal failure (somehow requires dialysis &

blood transfusions).


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Haemolytic Uremic

Syndrome(HUS)

Myocarditis,

other cardiovascular complications that mayresult in death.

central nervous system involvement,

hypertension.


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Reservoir ofE.coli

Raw or undercooked meat products,

raw milk,

fresh pressed apple juice or cider,

yogurt,

cheese,

salad vegetables,

transmission through direct contact betweenpeople and faecal contamination of water.


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LITERATURE CITED

Forsythe, S.J. The Microbiology of Safe

Food, Blackwell Science, Cambridge, 2000.

Wood, B. J. B., Microbiology of Fermented

Foods, Vol.1 and 2, Blackie Academic and

Professional, London, Second edition, 1998.

Documents

Industrial Lecture 8