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Chapter 36
Food and Foodborne Microbial
Diseases
Food Classification
Food Preservation Methods
1. Cold..refrigeration (4oC) , freezing (-20 to -80o C)
2. Pickling – Acidity….weak acids (pHs <5)
3. Drying – Dehydration….reduces water activity
4. Heating – pasteurization, boiling, autoclaving
a is Ok, something wrong b to d
Food Preservation Methods
1. Cold..refrigeration (4oC) , freezing (-20 to -80o C)
2. Pickling – Acidity….weak acids (pHs <5)
3. Drying – Dehydration….reduces water activity
4. Heating – pasteurization, boiling, autoclaving
5. High Pressure Processing..up to 100,000 lb/in2
6. Chemical Preservatives.
7. Irradiation.
International Symbol for Radiated Foods
Clicker Question:
Staphylococcal Food Poisoning
Clicker Question:
Staphylococcus aureus Toxins
TOXIN
ACTION
Hemolytic toxins
Animal cell lysis
Hyaluronidase
Breakdown of hyaluronic acid
Coagulase
Fibrin Formation
Staphylokinase
Fibrin Breakdown
Leukocidin
Kills WBC’s.
Epidermolytic toxin
Exfolation
Enterotoxins–A,B,C,D,E,F. Emetic Response
Enterotoxins
Small: 26-30 kD
Heat Stable – can resist boiling (unlike the bacterium!!)
Toxic Dose: as low as 1ng, usual is 1-5 μg (cells >105/g)
Emetic Response Mechanism
1. Direct on vagus nerve and sympathetic system.
2. Super Antigen (IL-2 mimics this response).
3. Both.
Diarrhea Mechanism – unknown, no c-AMP involvement
Incubation Period to Emesis
Classic Staph Food Poisoning: Cafeteria of a College
Dormitory…to the College Clinic (69 cases)
Foods
Involved
+
Symptoms
Botulism : Clostridium botulinum
Review of Endospore Location
Clostridium botulinum
Bacillus pasteuri
Bacillus cereus
Terminal Spore
Subterminal Spore
Central Spore
Clostridium Fermentations – From Glucose
What Can’t Clostridium spp Ferment?
In what types of Foods can C. botulinum
grow?
Clicker Question:
Botulism Toxin : Flaccid Paralysis
Botulism Toxin Effect on Motor Neurons
Infant Botulism: Floppy Baby Syndrome
Wound Botulism
Food Infection : Salmonella enterica
Peak in 1985 due to pasteurized milk mixed with raw (unprocessed) milk in
Illinois.
Salmonella enterica : over 1,400 Serovars
Salmonella enterica serovar Typhi is usually
abbreviated: Salmonella Typhi or S. Typhi.
Typhoid Fever has a very low incidence in USA,
only in people acquiring the disease outside USA.
However, all the other strains (servoars) cause the
data in the preceding figure: salmonellosis.
Reservoirs
Salmonella Taxonomy – Part 1
Gram Negative rods, facultative, catalase pos, oxidase neg
Closely related to Escherichia coli
Serogroups: 1941 – 100 serogropus of S. enterica
1964 – 900 serogroups
now - > 2,400 serogroups.
-based on H and O antigens.
IMViC -+-+, Lactose neg, all H2S pos.
H2S Production on TSI
Triple Sugar Iron Agar
1% sucrose
1% lactose
0.1% glucose
Na-thiosulfate
ferrous sulfate
Tryptone, Peptone
Yeast Extract
agar
Phenol red
pH 7.3
Left to Right: Control (uninoculated); Pseudomonas aeruginosa;
Escherichia coli; Salmonella Typhimurium; Shigella flexneri
Clicker Question:
H2S Production on TSI
Triple Sugar Iron Agar
1% sucrose
1% lactose
0.1% glucose
Na-thiosulfate
ferrous sulfate
Tryptone, Peptone
Yeast Extract
agar
Phenol red
pH 7.3
Left to Right: Control (uninoculated); Pseudomonas aeruginosa;
Escherichia coli; Salmonella Typhimurium; Shigella flexneri
Clicker Question:
Salmonella colonies XLT4 agar
Clicker Question:
Enteritis (Salmonellosis) Disease Characteristics
1. Incubation Period – mostly 6hrs to 2 days. ID50 = 10 to 106 cells
2. Symptoms: diarrhea, abdominal cramps, mild fever, nausea,
vomit, chills headache --- duration 2 – 3 days.
3. Therapy – non needed, antibiotic treatment gives no benefit.
Eat yoghurt!
4. Carrier state for a few months from bacteria in ileum and colon.
Adherence – mannose binding pili
Receptor mediated endocytosis  multiply intra-cellularly and
released to lamina propera  involvement of inflammatory cells
and release of prostaglandins  increase in c-AMP and
diarrhea (usually not toxin associated like cholera, but a few
have enterotoxins).
Salmonella World Wide
Clicker Question:
Infective Dose
Diagnosis, Treatment, Prevention
Diagnosis: Symptoms, culture organisms from fecal
sample .. and suspected food.
Isolates sent to other labs (Food Net and Pulse Net)
that use molecular methods of ID such as pulsefield gel electrophoresis of DNA fragments… pin
points the source of the outbreak.
Treatment: used to shorten course of disease and reduce the
carrier state…but multiple drug resistant Salmonella is a
significant clinical problem.
Prevention: cook your food. Infected individuals are banned (in
some states) from work as food handlers until their feces
are negative for Salmonella on three separate cultures.
E. coli can be both non-pathogenic and
pathogenic.
Normal human feces has 107 E. coli / gram
Feces have ~ 1012 bacteria / gram
Is E. coli dominant ?
How have some E. coli become pathogenic?
There are several major types of E. coli pathogens =>
This is STEC in your Text.