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1. Food Microbiology
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2. • TOPICS :
1.History of Microorganisms in Food
2.Taxonomy, Role, Microorganisms in Foods
3.Determining Microorganisms AND/OR Their Products in Food
4.Intrinsic and Extrinsic Parameters of Foods That Affect Microbial Growth
5.Microorganisms in Food :Meats and Poultry, Vegetable and Fruit Products,
Nondairy Fermented Foods and Products, Milk, Fermentation, and Fermented
and Nonfermented Dairy Products, Miscellaneous Food Products
6.Food Protection with Chemicals, Biocontrol
7.Radiation Protection of Foods
8.Protection of Foods with Low-Temperatures .
9.Food Protection with High Temperatures
10.Protection of Foods by Drying
11.High Hydrostatic Pressures (HHP)
12.Pulsed Electric Fields
13.Food Borne Disease

3. Food Microorganisms
 Bacteria
 Yeast
 Mold
 Viruses
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4. Harmful effects:
 Food borne disease
 Food infections
 Food poisoning
 Viral borne infections
 Food spoilage
Beneficial effects:
 Fermentation
◦ Cheese
◦ Yogurt
◦ Fermented sausages
◦ Wine
◦ Beer
◦ Pickles
◦ Sour kraut
 Probiotics
Pathogens

5. Food Microbiology
 spoilage: bad food
microbiology
– undesirable changes to
food; sour milk, moldy bread
– preservatives and
refrigeration inhibit the
growth of microorganisms

6.  smell bad, taste bad, look bad
 probably are not harmful
◦ microorganisms that cause food spoilage compete
with pathogens
◦ in the case of food spoilage vs. pathogens, the
spoilers are winning

7. Food Spoilage Microorganisms
bacteria yeasts molds
It is important to be able to distinguish food poisoning from food
spoilage
Food poisoning is when
food is eaten which looks
normal, smells normal
and tastes normal: you
eat enough to make you
ill from the ingested
pathogens or toxins
Spoiled food does not
normally cause food
poisoning because it is
rejected by the consumer
before ingestion

8.  Bacteria
◦ The Lactic Acid Bacteria (Lactobacillus
spp., Pediococcus spp., Leuconostoc
spp., etc.)
◦ Pseudomonas spp.
◦ Many others
 Fungi
◦ Molds and Yeast

10. Food Microbiology
 fermentation: good food
microbiology
– food that have been
intentionally altered such
as sour cream, cheese,
beer
– any desirable change a
microorganism makes to
food

11. Food-Borne Diseases
People get sick with a food-borne disease when they
consume foods or beverages contaminated with disease-
causing microbes, chemicals, insects or other harmful
substances
Illnesses Hospitalizations Deaths
Norovirus Salmonella (non-
typhoidal)
Salmonella (non-
typhoidal)
Salmonella (non-
typhoidal)
Norovirus Toxoplasma gondii
Clostridium perfringens Campylobacter Listeria monocytogenes
Campylobacter Toxoplasma gondii Norovirus
Staphylococcus aureus E. coli 0157 Campylobacter
Top 5 Germs Causing Illness, Hospitalizations, and
Deaths From Food Eaten in the United States

12. Probiotik
Pangan/suplemen pangan yang berisi
mikroba hidup yang memberi efek
menguntungkan (kesehatan) saluran
pencernaan

13.  Contamination pre-harvest
 Contamination during processing
 Fungi and bacteria are
everywhere!

14.  Soil and Water
 Plants and animals
 Raw to processed food / cross contamination
 Person to Food
 Person to Person

15.  Food spoilage
◦ results from growth of microbes in food
◦ involves predictable succession of microbes
◦ different foods undergo different types of
spoilage processes
◦ toxins are sometimes produced

16. •Water
•pH
•Physical structure
•Oxygen
•temperature

18. Microorganisms live in mixed communities
Many interactions are cooperative
Waste of one organism represents a nutrient for another
Some cells compete for nutrients
Synthesize toxic substance to inhibit growth of competitors

19. Time
Lag Phase
Stationary Phase
Death
Phase
Bacterial Growth Curve
Number
of
Bacteria
(log10)

21. Time
Changing the Bacterial Growth Curve
*Sub-optimal means lowered: pH, AW,Temp., etc.
Much longer Lag Phase
Number
of
Bacteria
(log10)

22. Microorganisms in Food
 factors that affect the presence of
microorganisms in food include
– intrinsic
– extrinsic

23. Intrinsic Factors
1. composition
2. physical structure
3. pH
4. presence and availability of water
5. presence of antimicrobial substances

24. Exntrinsic Factors
1. temperature of storage
2. relative humidity of environment
3. presence and concentration of gases
4. presence and activities of other
microorganisms

25. Factors Affecting Microbial
Growth in Foods
What are the factors affecting
microbial growth in foods?
F-
A-
T-
T-
O-
M-
(P)-

26. F (“Food” for the microbes to eat)
Nutrients in food affect microbial growth:
• Sources of energy (e.g., sugars, proteins)
• Sources of nitrogen (e.g., proteins)
• Vitamins
• Minerals
In order for bacteria to grow, the food has to
have the right nutrients for the bacteria and
the bacteria have to be able to “get to” the
food...

27. Chemical Requirements
 #1 = water!
 Elements
–C (50% of cell’s dry weight) HONPS
–Trace elements
 Organic
–Source of energy (glucose)
–Vitamins (coenzymes)
–Some amino acids, purines and
pyrimidines

28. 28
WATER
 Used to dissolve materials to be transported
across the cytoplasmic membrane

29. OSMOTIC PRESSURE
 Bacteria 80-90% water
 High salt in surrounding environment leads to water
loss and plasmolysis
 Cell’s plasma membrane shrinks, cell growth
inhibited

30. Fig. 7.4

31. Effect of nutrients on microbial growth
 Microorganisms depend on nutrients for both
energy and growth.
 Different microorganisms possess different
enzyme systems which are specific in breakdown of
certain nutrient compounds.
 Microbial growth can be enhanced by enriching the
growth medium with specific nutrients
 Creating specific nutrient media is a very useful
tool both in laboratory work and in industry for
isolation and growth of certain microorganisms.

32.  Physical structure
– grinding and mixing increase surface area and
distribute microbes
 promotes microbial growth
– outer skin of vegetables and fruits slows
microbial growth

33. • So the “biological
structure” of the
food is important:
– Plants have outer
“skins” which
protect them from
microbial growth
– What happens
when the skin is
damaged (or cut
into like this
watermelon)?

34.  Acidity (pH)
Microorganisms are able to grow in an environment with a
specific pH
Microoganism
s
Min. pH value Opt. pH value Max. pH value
Gram +ve
bacteria
4.0 7.0 8.5
Gram –ve
bacteria
4.5 7.0 9.0
Yeasts 2.0 4.0- 6.0 8.5- 9.0
Molds 1.5 7.0 11.0

35. Clarification of Acidity (pH)
•intracellular pH is relatively near
neutrality

36. Acid (pH)
• Microorganisms grow best at pH near 7
– As the pH goes lower, if microorganisms grow, they
grow slower
• Most pathogens do not grow or at least don’t
grow well at pH < 4.6
– However, they may survive at least for a short time at
low pH
• Many yeast, molds, and spoilage bacteria can
grow at pH < 4.6
– Why is this important?

37. Some bacteria are:
 Acidophilic bacteria e.g. Lactic acid bacteria (pH
3.3 – 7.2) and acetic acid bacteria (pH 2.8 – 4.3).
 Basophilic bacteria e.g. Vibrio parahaemolyticus
(pH 4.8- 11.0) and Enterococcus spp (pH 4.8-
10.6).
 Increasing the acidity of foods either through
fermentation or the addition of weak acids could
be used as a preservative method.

38. pH
 most acidophiles and alkalophiles maintain
an internal pH near neutrality
 some use proton/ion exchange
mechanisms to do so
 some have Acid Tolerance Response
(synthesize proteins that provide protection)
 e.g., acid-shock proteins

40. pH scale:

41.  neutrophiles
◦ optimum pH of 7 (neutral)
◦ most microorganisms grow best between pH of 5
(acidic) and pH of 8 (alkaline)
 acidophiles
◦ optimal growth, pH of less than 5.5
 alkalophiles
◦ optimum pH of 8.5 or greater
Copper
Copper tolerant acidophile
Urinary bacterial infection
caused by alkaline urine

42.  The acidophiles have modifications of their
membrane that allow them ot adjust their
cytoplasmic pH with proton pumps

43. Temperature and Time
• Classifying bacteria by growth
temperatures:
– Thermophiles(very hot)
– Mesophiles (cool to very warm or hot)
– Psychrotrophs (cold or warm)
– Psychrophiles (only cold)
• In food microbiology, we are most concerned
with mesophiles and psychrotrophs

44.  5 divisions of
prokaryotes, based on
optimal growth
temperature
◦ psychrophiles
◦ psychrotrophs
◦ mesophiles
◦ thermophiles
◦ hyperthemophiles
Psychrophile:
Desulfofaba gelida
Thermophile:
Pyrococcus sp.
Hyperthermophile:
Thermococcus barophilus

45. TEMPERATURE OPTIMA
 Psychrophiles: cold-loving
 Mesophiles: moderate temperature-loving
 Thermophiles: heat-loving
 Each has a minimum, optimum, and
maximum growth temperature

46. ◦ temperature growth range
 minimum to maximum temperatures for bacterial
growth
◦ optimal growth temperature
 temperature at which the highest rate of reproduction
occurs

47.  Optimum growth temperature is usually
near the top of the growth range
 Death above the maximum temp. comes
from enzyme inactivation
 Mesophiles most common group of
organisms
 40ºF (5°C) slows or stops growth of most
microbes

48. Enzymes exhibit a Q10 so that within a suitable
temperature range the rate of enzyme activity
doubles for every 10' C rise in temperature.

49. Classification of Bacteria by
Temperature Requirements

50. EFFECT OF TEMPERATURE ON THE GROWTH
In food microbiology mesophilic and psichrotrophic organisms are
generally of greatest importance.
Mesophiles, with temperature optima around 37 °C, are frequently of
human or animal origin and include many of the more common food
borne pathogens such as Salmonella, Staphylococcus aureus and
Clostridium perfringens.
As a rule mesophiles grow more quickly at their optima than
psychrotrophs so spoilage of perishable products stored in the
mesophilic growth range is more rapid than spoilage under chill
conditions.

51. EFFECT OF TEMPERATURE ON THE GROWTH
True or strict psychrophiles
(’cold-loving’) have optima of 12-15 °C and will not grow
above about 20°C.
Psychrotrophs or facultative psichrophiles will grow down
to the same temperatures as strict psychrophiles but
have higher optimum and maximum growth temperatures.
This tolerance of a wider range of temperature means
that
psychrotrophs are found in a more diverse range of
habitats and consequently are of greater importance in
the spoilage of chilled foods.

52. • Refrigeration (< 41°F)
– Slows or stops pathogen growth
– Most pathogens don’t grow in refrigerated foods
– However, a few pathogens can grow slowly
under refrigeration (they are psychrotrophs)
• Listeria monocytogenes
• Yersinia enterocolytica
• Aeromonas hydrophila
• Clostridium botulinum type E
– Many spoilage microbes are psychrotrophs
• Freezing does not kill bacteria
• Some may die when frozen, but this can’t be counted on

53.  food preservation
◦ refrigeration
 inhibits fast growing
mesophiles
◦ Psychrotroph can still grow in
refrigeration, but at a
diminished rate
◦ freezing destroys
microorganisms that require
water to grow

54. EFFECT OF TEMPERATURE ON THE GROWTH
Thermophiles are generally of far less importance in food
microbiology, although thermophile spore formers such as
certain Bacillus and Clostridium species (Bacillus
stearothermophilus, Clostridium thermosaccharolyticum)
could cause problems in tropical canned foods.

55. • Heat
– Cooking to > 165°F kills most pathogens
• Remember which ones aren’t killed/destroyed?
– Spores, toxins
– If food is held on a hot serving line at >
140°F, pathogens can NOT grow or produce
toxins

56. Fig. 19-4, p. 669
40°F - 140°F = 4°C - 60°C

57. Bacteria die if heated
for a sufficient time.
The longer the time, the
greater the destruction
Bacteria stop growing,
but do not die
4
Bacteria
grow
quickly
100
63
40
38
36
15
7
0
• Pathogenic bacteria grow best at
human body temperature 37ºC.
However the majority will grow
between 15-45ºC
• Non-sporing cells of bacteria are
killed at temperatures above 60ºC.
The length of time
ranges depending on the organism
• Boiling kills living cells, but will not
kill all bacterial spores
• Fridges should be set below 5ºC.
Some bacteria such as Listeria
monocytogenes can grow at
refrigeration temperatures
Bacteria
Grow
at slower
rate
Bacteria
grow

58.  psychrophiles
◦ optimum growth temperature:
-50C – 150C
◦ found in the Arctic and
Antarctic regions of the world
Bacteria found in melt
from a Russian outpost
on Lake Vostok
Desulfofrigus oceanense

59.  psychotrophs
◦ optimum growth
temperature: 200C
– 300C
 will grow at lower
temperatures
◦ most commonly
found in
refrigerated food
spoilage
Stemphlium sarcinaeforme

60.  mesophiles
◦ optimum growth temperature:
250C – 450C
 most human pathogens are
mesophiles
 adapted well to growth in
the human body, whose
normal temperature is
around 370C
Salmonella

61.  thermophiles
◦ optimum temperature: 450C –
700C
◦ commonly found in compost
heaps and hot springs, water
heaters
Sulfur pots in Yellowstone
Sulfolobus
Thermophile in a hot spring

62.  hyperthermophiles
◦ optimum growth
temperature: 700C – 1100C
◦ usually member of the
Archae domain
◦ found in hydrothermal
vents in the depths of the
ocean
Deep Sea Vent

63.  Microorganisms that grow at optimal
temperatures of 45oC and above are
thermophiles
 They can belong to Archaea and Bacteria
 Soils in the desert and tropical areas can be
warmed to 70oC or above.
 Compost and silage( farms reach
temperatures of 60oC or higher
 Hot springs

64.  Geysers and hot springs such as those at
Yellowstone can reach temperatuers of 150-
500oC
 Hydrothermal vents spew superheated steam
from the ocean floor

65.  Both terrestrial environments and aquatic
environments experience cold termperatures
 Organisms grow in these environments
throughout the year as long as there are
pockets of water.
 A psychrophile grows at an optimal
temperature of 15oC or lower
 Psychrotolerant organisms can also grow at
low temperatures but can grow better at
temperatures of 20oC or higher

66.  Cold resistant enzymes and proteins contain
higher amounts of alpha helices in their
proteins
 The alpha helix provides greater flexibility
 Active transport occurs at lower temperatures

67.  Membranes contain polyunsaturated fatty
acids and long chain hydrocarbons with
multiple double bonds.

68. TIME

69. In ideal conditions where there is
Moisture, Food and Warmth
(37degrees centigrade is ideal),
bacteria can double every 10 to 20
minutes. They do this by dividing
in to two. This is called
Binary Fission

70. These cells are beginning to divide into two

71. After 10 minutes
After 20 minutes
After 30 minutes
After 40 minutes

72. Time : 9.30 Bacteria : 0
Time : 9.40
Time : 9.50
Time : 10.00
Bacteria : 12,000
Bacteria : 24,000
Bacteria : 48,000
Time : 10.10
Time : 10.20
Time : 10.30
Time : 10.40
Time : 10.50
Bacteria : 96,000
Bacteria : 192,000
Bacteria : 384,000
Bacteria : 768,000
Bacteria : 1.5 million
From 0 to 1,536,000 in
only 80 minutes !!!!!!
Knife contaminated
by blood
cooking chicken to a core temperature of 75°C should kill
most of the bacteria

73.  Obligate aerobes – require O2
 Facultative anaerobes – can use O2 but also
grow without it
 Obligate anaerobes – die in the presence of
O2

74.  Aerotolerant – do not use O2 but can grow
when it is present
◦ Often ferment glucose to lactic acid
 Microaerophiles – require O2 but grow only in
concentrations lower than air

75. Figure 6.15
need
oxygen
prefer
oxygen
ignore
oxygen
oxygen is
toxic
< 2 – 10%
oxygen

76. oxygen relationships of microorganisms:

77. Classify the
Growth in each
tube:
 Aerotolerant
anaerobe
 Facultative
anaerobe
 Microaerophile
 Obligate aerobe
 Obligate
anaerobe

78. Toxic Forms of Oxygen
 Singlet oxygen (1O2) – very reactive
 Superoxide free radicals (O2
.)
 Neutralized by superoxide dismutase (SOD)

79. Toxic Forms of Oxygen
 Peroxide anions (O2
-2)
 H2O2 broken down by catalase and peroxidase
 Hydroxyl radical (OH-) –very reactive

80. Protections of bacteria against
oxygen
 Bacteria possess protective enzymes, catalase
and superoxide dismutase.
 Catalase breaks down hydrogen peroxide into
water and oxygen gas.
 Superoxide dismutase breaks superoxide
down into peroxide and oxygen gas.
 Anaerobes missing one or both; slow or no
growth in the presence of oxygen.
Fe3+ -SOD + O2
- → Fe2+ -SOD + O2
Fe2+ -SOD + O2
- + 2H+ → Fe 3+ -SOD + H2O2

81. toxic forms of oxygen:

82. enzymes that destroy toxic oxygen species:

84. Fig. 7.10b

85. Candle jar
 Provides
low O2,
high CO2

86. Catalase Test
 Aerobic organisms like Staphylococcus and
Streptococcus possess a mechanism for destroying
hydrogen peroxide and the hydroxyl radical two toxic
products of aerobic respiration
 When hydrogen peroxide is added to a slant of bacterial
growth – the breakdown of hydrogen peroxide indicates
the presence of the enzyme Catalase
catalase
H2O2 + H2O2 2 H2O + O2

87. Moisture (Water)
Effect of moisture on microbial growth
 Water is essential for the growth of all living
organisms. Has many important functions in
the
growth of microoranisms and in enzyme
activity.
 Preserving techniques such as dehydration,
concentration, freezing are based on making
water
unavailable for the microorganisms.


88. Water activity (aw)
Water activity is a measure of the water
available for microorganisms to grow
 The water activity of a food ranges
from 0.00 – 1.00
 Aw of a completely dehydrated food is 0.00
 Aw water is 1,00

89.  No growth of any microbe below aw = 0.60
Exceptions are :
 Halophilic bacteria (min. aw = 0.75, Halobacter spp),
 Xerophilic molds (min. aw = 0.60, Xeromyces bisporus)
 Osmophilic yeasts (min. aw = 0.60, Zygosaccharomyces
rouxii).

90.  It is a ratio of water vapour pressure of the food substance
to the vapour pressure of pure water at the same
temperature.
 Water activity (aw) = P/ Pw where P= water vapour
pressure of the food substance and Pw= water vapour
pressure of pure water (Pw = 1.00).
Microoganisms Minimum water activity (aw)
values
Gram +ve bacteria 0.95
Gram –ve bacteria 0.91
Yeasts 0.88
Molds 0.80

91. EFFECT OF WATER ACTIVITY ON THE
GROWTH
Practically, apart from a few osmophilic yeasts and
xerophilic fungi, below the aw of 0.7 there is no
microbial growth.
In the food microbiology, this aw=0.7 is the critical
value. However, it is important to emphasize that,
even if active growth is impossible, survival may still
occur and many microorganisms can survive at very
low water activities and are frequently stored in
culture collections in this form
Water activity

93. Water activity and microbial growth
–Most bacteria can’t grow below aw = 0.85
–Most yeasts & molds can’t grow below aw = 0.65
Relative
growth
or
reaction
rate
Water activity
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0 0.9

94. WATER ACTIVITY OF SOME FOODS
________________________________________________________
Food aw
________________________________________________________
Fresh vegetables, meat, milk, fish 0.98<
Cooked meat, bread 0.95 – 0.98
Cured meats, ham, cheeses 0.91 – 0.95
Dry cheeses, salami 0.87 – 0.91
Flour, rice, beans, cereals 0.80 – 0.87
Jams 0.75 – 0.80
Dried fruits, caramels 0.60 – 0.75
Spices, milkpowder 0.20 – 0.60
________________________________________________________

95. TYPICAL WATER ACTIVITY OF SOME FOODS
0.95 – fruits, vegetables, meat, fish, milk
0.91 – some cheeses, ham
0.87 – salami, pepperoni, dry cheeses, margarine,
0.80 – fruit juice concentrates, sweetened condensed milk, syrups,
flour, rice, high sugar cakes
0.75 – jam, marmalade
0.65 – oatmeal, fudge, marshmallows, jelly, molasses, sugar, nuts
0.60 – dried fruits, honey
0.50 – dried pasta, dried spices
0.30 – cookies, crackers
0.03 – dry milk, dehydrated soups, corn flakes
Aw – examples

96. LOW WATER ACTIVITY:
HALOPHILES, OSMOPHILES, AND XEROTOLERANT
 Water is critical for life; remove some, and things can’t
grow
 Halophiles/halotolerant: relationship to high salt.
 Marine bacteria; archaea and really high salt.
 Osmophiles: can stand hypertonic environments
whether salt, sugar, or other dissolved solutes
 Fungi very good at this.
 Xerotolerant: dry. Subject to desiccation. Fungi best
 Bread, dry rot of wood
 Survival of bacterial endospores.

97. Mainly 3 methods for making water unavailable:
1. Increasing the solute concentration;
removing water, adding of solutes (salt,
sugar)
2. Addition of hydrophilic (water-binding)
colloids (gels, pectins, gums)
3. Bringing water to a solid phase (freezing)

98.  Most bacterial pathogens can not grow or
produce toxins at AW < 0.91
 Exception: Staph. aureus can grow and
produce toxin down to 0.85
 How do you think AW can be decreased?
 1.
 2.
 3.
 How do these methods work?

99. DRYING AND HIGH OSMOLARITY
 Salted fish, jerky, honey, sweetened condensed
milk are preserved by pulling water out of bacteria
 Hypotonic medium (low osmolarity) may lyse
bacteria without cell walls

100. salt tolerance:

101.  Halophiles
◦ bacteria that specifically require NaCl for growth
 Moderates
◦ grow best at 3% NaCl solution
◦ many ocean dwelling bacteria
 Extreme
◦ grow well at NaCl concentrations of greater than
15%
 salt lakes, pickle barrels
102

102.  Halophiles growing within salt lakes
often turn the water pink
 this sometimes occurs in Great Salt Lake,
Utah
103

103.  Staphylococcus are salt tolerant up to
concentrations of 10% NaCl
 grow on surface of skin
104

104.  halophiles are microorganisms that have adapted
to this kind of environment
◦ halophiles
 require high levels of sodium chloride
 moderate halophiles
 3% salt concentration
 extreme halophiles: Archaea
◦ require at least 9% salt solution
◦ found in the Dead Sea
Dunaliella salina cell, near a salt crystal.
40X
Dead Sea
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105. The stability of some foods against attack
by microorganisms is due to the presence
of certain naturally occurring substances
that possess and express antimicrobial
activity.

106.  Antimicrobial substances
◦ coumarins – fruits and vegetables
◦ lysozyme – cow’s milk and eggs
◦ aldehydic and phenolic compounds – herbs and
spices
◦ allicin – garlic
◦ polyphenols – green and black teas

107. Natural constituents of foods which
affect microbial growth are:
 Lysozyme e.g. Eggs
 Lactoferrin e.g. Milk
A. Lactoperoxidase e.g. Cow’s milk
 Conglutinin e.g. Cow’s milk
 Essential oils e.g. Spices and vegetables
Preservatives such as benzoic acid, sorbic
acid and nisin

108. tks

109. • Growth of microbes in
food follows a typical
microbial growth pattern
• Growth rate depends on
the nutritional value and
temperature of the food
• Number of microbes depends on both inoculum size and
growth rate
• Food spoilage occurs at high populations density
(at stationary phase) - retarding microbial growth delays
spoilage

110. Microbial Growth and Food Spoilage
Meats and dairy products are ideal
environments for spoilage by
microorganisms because of their high
nutritional value and the presence of
easily utilizable carbohydrates, fats,
and proteins; proteolysis (aerobic) and
putrefaction (anaerobic) decompose
proteins;

111. Fruits and vegetables have much
lower protein and fat content than
meats and dairy products and undergo
different kind of spoilage;
the presence of readily degradable
carbohydrates in vegetables favors
spoilage by bacteria; high oxidation-
reduction potential favors aerobic and
facultative bacteria; molds usually
initiate spoilage in whole fruits

112. Frozen citrus products are minimally
processed and can be spoiled by lactobacilli
and yeasts
Grains, corn, and nuts can spoil when held
under moist conditions; this can lead to
production of toxic substances, including
aflatoxins and fumonisins
Shellfish and finfish can be contaminated by
algal toxins, which cause of variety of
illnesses in humans

113. Food preservation:
 Temperature
 Lower: decreased growth
rate - but, psychrophilic
microbes
 Perishable food will only
last for a few days at 4
oC
 Freezing ( - 20 oC)
destroys the texture of
many products and does
not completely stop
growth
 Deep freezing (- 80 oC) is
costly
 Acidity
 Most foods at neutral or
acidic pH
 At pH < 5 microbial growth
is inhibited
 Pickling: Decreased food pH
by the addition of vinegar
(acetic acid bacteria);
veggies, meats, fish
 Fermented foods: acid is
produced during food
production (e.g.,
sauerkraut, yogurt, etc);
lactic acid, acetic acid, and
propionic acid bacteria;
limited to pH > 4

114. Food Preservation:
preventing growth and metabolic
activities of microorganisms
 spices, salting, drying are methods that
have been around for years
 most common methods of current food
preservation are
 high temperature treatment
 low-temperature storage
 antimicrobial chemicals
 irradiation

115.  The microbial agent causing spoilage
depends on the source of the food and
its nutritional value:
 Meats may be contaminated by intestinal
pathogens released during slaughter
 Dairy products - lactic acid bacteria
 Fruit and vegetables - soil and water
microbes
 Some microbes that cause spoilage may
be human pathogens but the majority
are not!

116. Controlling Food Spoilage
1. Removal of microorganisms-filtration of water, wine,
beer juices, soft drinks and other liquids
2. Low temperature-refrigeration and/or freezing
retards microbial growth but does not prevent spoilage
3. High temperature
Canning
Canned food is heated in special containers
called retorts to 115°C for 25-100 minutes to kill
spoilage microorganisms

117. Pasteurization-kills disease-causing organisms;
substantially reduces the number of spoilage
organisms
•Low-temperature holding (LTH)-68°C for 30
min
•High-temperature short-time (HTST)-71°C for
15 seconds
•Ultra-high temperature (UHT)-141°C for 2
seconds
•Shorter times result in improved flavor and
extended shelf life

118. •Water availability-dehydration procedures
(e.g., freeze-drying) remove water and
increase solute concentration
•Chemical-based preservation
•Radiation-nonionizing (ultraviolet or UV)
•Microbial product-based inhibition
Bacteriocins-bacteriocidal proteins produced
by bacteria; active against only closely
related bacteria (e.g., nisin)

120. What are Food-Borne Diseases?
People get sick with a food-borne disease when they
consume foods or beverages contaminated with
disease-causing microbes, chemicals, insects or other
harmful substances.
Bacteria, viruses and parasites cause most of these
diseases. Toxins, poisons and chemicals can also
contaminate food and cause illness.

121. Food-Borne Diseases
 two primary types
 food-borne infections
 food intoxications

122. •There are a reported 76 million cases of food-borne
disease occurring every year in the United States alone.
•Most of these cases are mild and cause symptoms for a
day or two. More serious cases require 323,000
hospitalizations annually, and even cause 5,000 deaths a
year.
•People most at risk tend to be those who are very old,
very young, women who are pregnant.
• Even robustly healthy people are vulnerable if they are
exposed to a very high dose of an unhealthy organism.

123. One symptom these diseases produce in common is
that because they enter the body through food, the first
sign of illness is usually nausea, vomiting, abdominal
pain and cramps and diarrhea.
the spectrum of food-borne diseases constantly changes
and evolves even as the science of food safety continues
to make significant advances and discoveries.
Some diseases, such as cholera, tuberculosis and
typhoid fever have been eradicated thanks to food safety
improvements.
Other diseases are just now being discovered or are
adapting and evolving into new strains. E.Coli 0157:H7,
for example, didn't exist 25 years ago.

124. Foodborne diseases and microbial
sampling:
 Food poisoning - Caused by preformed toxin in
the food; organism may or may not be alive and
growing; Clostridium botulinum and
Staphylococcus aureus
 Food infection - Live cells delivered by
contaminated food; organism multiply once food
is ingested; Salmonella
 Sampling: Process food to release microbes;
culturing and use of molecular probes
(antibodies, gene probes, PCR) to detect specific
microbes

125. Examples of foodborne diseases
most are infections and associated with animal
products:
Organism Number of cased
per year (U.S.)
Foods to watch
Campylobacter jejuni 1,963,000 Poultry and diary
products
Salmonella spp. 1,340,000 Poultry, meat, diary
and eggs
Clostridium
perfringens
248,000 Cooked and reheated
meat products
Giardia lamblia 200,000 Contaminated meat
Norwalk-like viruses 9,200,000 Shellfish, other food

126. Staphylococcus aureus:
 Common skin, respiratory, and GI tract flora
 Grows readily in unrefrigirated meats and
creamy foods; toxins are heat resistance
 Produces 7 entrotoxins; the most potent is A
(entA); a superantigen (T cell stimulation 
cytokines  intestinal inflammation 
gastroenteritis)
 Severe but short response (1-6 hrs following
ingestion; done by 48 hrs)
 Detection of toxins or the organism in food
 Antibiotics are useless

127. Clostridial diseases:
 Gram positive, spore-forming, anaerobes common in
soil; C. perfringens and C. botulinum
 C. perfringens - food poisoning: ingestion of > 108
cells (inappropriate cooking followed by
unrefrigirated storage in closed containers)  spore
germination in the intestine leads to neurotoxin
production
 Alteration of water permeability of intestinal lining 
diarrhea and intestinal cramps (no vomiting or fever);
onset within 7 - 16 hrs of ingestion but gone in 24
hrs
 Diagnosed by isolation of microbe or detection of
toxin in feces

128. Botulism (C. botulinum):
 The most potent toxin
known; few cases but high
mortality (25%); destroyed
by 10 min in 80 oC
 Flaccid paralysis of muscles
 Common in soil and water
 How? Improper canning 
spore germination  toxin
production  canned food
used without cooking 
disease
 Infant botulism: consumption
of honey that is contaminated
by spores (0 - 2 months)
 Treatment: antitoxin and
ventilation

129. Salmonellosis:
 Gram negative enteric
bacterium; all strains are
pathogenic; transmission is
from sources (eggs, meats)
and by food handlers
 Colonization of of intestinal
epithelium
• Two diseases:
– Enterocolitis (most commonly by S. typhimurium): 105 - 108 viable
cells; disease onset within 8 - 48 hrs; headaches, chills, vomiting,
diarrhea and fever (2-3 days); continuous shading of organism for
months/years (Typhoid Mary); treatment - none
– Typhoid fever (S. typhi): Septicemia leading to high fever that can last
for several weeks; mortality is 15% if untreated; antibiotics
• Prevention: Cooked food (70 oC for 10 min); monitor for carrier state
among food handlers

130. Pathogenic E. coli:
 Some strains of E. coli; diarrhea and urinary tract infection;
classification of pathogens is based on toxin and diseases
 Enterohemorrhagic (O157:H7) - colonization of the small
intestine and verotxin production  diarrhea and kidney
infection; uncooked and undercooked ground meat; occasional
epidemics
 Enterotoxigenic (Travelers diarrhea) - heat labile toxin; water
and produce in developing countries; immunity
 Enteropathogenic - diarrhea that afflicts young children
 Enteroinvasive - invasive colon infection; bloody diarrhea;
survival in phagosomes; in developing countries
 Treatment and prevention: diseases are self-contained but
antibiotics help; irradiation of ground beef!

131. Campylobacter:
 Gram negative microaerophile common in
poultry and sometimes in beef
 C. jejuni and C. coli  bacterial diarrhea; C.
fetus  spontaneous abortion in livestock
 Ingestion of 104 cells  colonization of small
intestine  inflammation  high fever (104
oC), headache, malaise, nausea, cramps,
diarrhea  subsides in 1 week; erythromycin
to shorten infectious stage
 Prevention by proper cooking and hygiene
(including utensils)

132. Listeriosis:
 Listeria monocytogenes: a gram (+) bacillus; Cold and salt
tolerant; wide distribution; found in soil water and raw milk;
contaminates all food products either at source or during
processing; mostly in processed food
 Pathology (2500 per year):
 Uptake by phagocytes  growth  lysis of phagocyte 
infection of nearby cells
 Immunity due to cell-mediated TH1 cells  macrophage
activation
 In normal individuals - gastrointestinal food infection; in
immuno-compromised individuals - acute bacterimia and
meningitis (20% death rate)
 Prevention: cleanliness during food processing; avoiding
outdated foods
 Diagnosis by culturing from blood and spinal fluid; treated with
trimethoprim drugs

133. Other foodborne infectious
diseases :
 Bacterial diseases
 Yersinia enterocolitica -
enteric fever
 Bacillus cereus - food
poisoning by heat stable
toxin
 Shigella spp. - shigolosis
(100,000 per year)
 Vibrio spp. -
contaminated seafood
 Viral diseases - the
most common cause of
gastrointestinal diseases;
“24-hour flu” - fast and
self-containing; fecal
contamination
 Norwalk viruses,
rotaviruses, astroviruses,
hepatitis A

134. Preventing Foodborne Disease
•Food infections (microbes are transferred to
consumer)
•Food poisoning (results from the toxin
consumption)

136. Food-Borne Intoxications
 ingestion of toxins in foods in which
microbes have grown
 include staphylococcal food poisoning,
botulism, Clostridium perfringens food
poisoning, and Bacillus cereus food
poisoning

137. Toxins
 ergotism
 toxic condition caused by growth of a
fungus in grains
 aflatoxins
 carcinogens produced in fungus-infected
grains and nut products
 fumonisins
 carcinogens produced in fungus-infected
corn

139. Adaptations of
thermophiles
 protein structure stabilized by a variety of means
 more H bonds
 more proline
 histone-like proteins stabilize DNA
 membrane stabilized by variety of means
 more saturated, more branched and higher molecular weight
lipids
 ether linkages (archaeal membranes)

140. Oxygen (Oxidation
- R
eduction Potential)
• O-R potential generally refers to the
amount of oxygen present
• Pathogens:
– Most bacterial pathogens can grow with
or without Oxygen (Facultative
anaerobes)
– Some food pathogens can only grow
when no Oxygen is present (anaerobes)
• Example?