Various Factors affect the nature and extent of the normal flora Microbiology of Food and Milk Microbiology of Water

1. Normal Flora of the
Human Body

2. -many organs and sites in the healthy human host
are free of microorganisms. These include the
cerebrospinal fluid, blood, urinary bladder, uterus,
fallopian tubes, middle ear, paranasal sinuses
and kidneys.
It is estimated that the adult human body is host to al
least 100 trillion microbial cells at any time.

3. Normal Flora
-indigenous microorganisms, most of which
are bacteria
-they inhabit the skin and some of the inner
surfaces of the body (such as the skin,
mouth, nasopharynx, ears, intestinal tract,
and lower urogenital tract)
-sex of the host may also influence the
composition of the normal microbial flora

4. -species, no. of normal flora sometimes depends
at particular ages of the host.
-members of the normal flora may also be
thought of as the resident flora (those microbes
regularly found in a given site at particular host
age).
-are harmless they do not cause disease unless
they become opportunistic pathogens (which
cause infections if tissue injury occurs at specific
body sites or if the resistance of the body to
infection is decreased)

5. Various Factors affect the nature and extent of the normal flora:
1. weather (inc T & humidity, inc density of skin microflora)
2. age has an effect (young children has more varied microflora
and carry more G- bacteria, potential pathogens than
adults)
3. hospitalized patients (> no. Of pathogens and antibiotic-
resistance organisms than normal people)
4. personal hygienic habits influence the resident microflora and
unclean individuals have higher population densities)

8. Transient flora
-simply harbored for a short time by the
human body
-may be present only for several hours,
days, or weeks,and then disappear

9. Distribution and Occurrence of the Normal Flora
1. Blood, Body fluids, and tissues
-occasional microbes may cross protective
epithelial barriers as a result of trauma, such as
tooth extraction and child birth
-microbes found in the bloodstream for a brief
time such transient bacteremia may cause
infection of damaged or abnormal heart valves
leading to subacute bacterial endocarditis
(inflammation of the membrane lining the heart
and its valves)

10. 2. Skin -1st line of defense
-several factors responsible for discouraging
microbial growth on the skin:
1. dryness -102 to 104 bacteria per
square centimeter)
2. low pH- between pH 3 to 5
3. inhibitory substances- eg. Sweat glands
(lysozyme-enzyme that destroy the
peptidoglycan of bacterial cell walls)
-sebaceous glands- secretes complex
lipids which may be partially degraded by
bacteria such as Propionibacterium acnes to
produce long-chain fatty acids, such as oleic
acid (highly inhibitory to other bacteria)

11. 3. Eye
– has conjunctiva(membrane lining the
eyelids which continually washed by a flow
of tears-tends to remove microorganisms
(has lysozyme)
4. Respiratory tract
a. Upper respiratory tract
b. lower respiratory tract

12. 5. Mouth- S. mutans (produces glucan that is formed
only in the presence of sucrose)
Dental plaque
- aggregation of bacteria and organic matter on
the surface of the teeth.
-contains a very high number of bacteria, 108
cells per milligram
6. Gastrointestinal tract
a. Stomach
b. small intestine
c. large intestine- has the largest microbial popn
7. Genitourinary tract

13. Effect of Normal Flora on the human host
Three approaches have been used to answer this
A. Use of germfree animals(helpful in understanding the fxns of NF of
humans
-germfree life (practical tools for solving problems of importance in biology
and medicine)
-able to study the effects of microorganisms added to germfree
animals
Gnotobiotic-animals that are raised in an environment with one or more
known microorganisms
Germfree animals vs. Normal Animals
1. GA have underdeveloped immune system(making them unusually
susceptible to infection if exposed to microorganisms). They lack
antibodies to normal flora antigens, which often share similarity to the
antigens of disease-causing microorganisms and confer partial protection
against these pathogens.

14. 3. GA require higher levels of B vitamins in their diet than do normal
animals; they also require vit K, which normal animals do not require in
their diet(this indicates that the normal flora makes a significant
contribution to satisfying the vitamin requirements of the host).
2. GA are vulnerable not only to pathogenic bacteria but also to non-
pathogenic ones. This is bec immunologic priming (a buildup of
resistance to pathogens) has not occured under the protection of
maternal antibodies soon after birth

15. B. Use of antimicrobial agents.(If the balance that occurs
between the NF and the human host is altered by use of
antimicrobial agents, the effects are useful in understanding
the role of the normal flora).
-examples:
1. treating the skin of humans with antibacterial agents,
such as hexachlorophene, suppresses colonization by the
normal G+ microbes and promotes growth and clinical
infection by G- rods and other microorganisms not
normally able to cause infection
2. hospital patients receiving antibiotics may lose much of
the normal flora of the large bowel, leading to
pseudomembrane colitis-a severe disease caused by
excessive growth of toxin-producing strains of anaerobic
spore-forming bacterium, Clostridium difficile, which
normally is absent or is only a minor component of the
normal flora.

16. 3. The yeast Candida albicans , a minor component of
the normal flora may multiply dramatically following
antibiotic therapy(since it is EUCARYOTE, resistant to
antibacterial antibiotics)
C. albicans can cause diarrhea and superficial fungal
infections in the mouth, vagina or anal area
C. Knowledge of certain characteristics of the normal flora that
inhibit the growth of other microbes. These characteristics
suggest that normal flora organisms may help to discourage
the growth of microorganisms that are not part of the
indigenous flora.

17. Characteristics of Normal Flora Organisms
-these properties may include physical characteristics such as:
1. Adherence to host cells
-many species of the normal flora can adhere to the surface of host epithelial cells, the
tissue cells that cover body surfaces.
-allows the bacteria to multiply while they avoid removal by the flushing effects of
surface fluids and peristalsis(a progressive wave of contraction that forces contents
toward an opening)
eg. Streptococcus salivarius –adheres mainly to the surface of the tongue
Streptococcus mutans –selectively binds to the smooth enamel surface of the teeth
-desquamation, a phenomenon that affects microbial adherence (detachment of host
epithelial cells from body surfaces and replacement of the lost cells by new cells)- in
body sites like intestinal tract

18. 2. Production of antimicrobial substances
- some resident microorganisms produce metabolic products
that can inhibit other microbes.
eg. In the large intestine-certain anaerobic bacteria produce
organic acids such as acetic, lactic, or butyric acid as
metabolic waste products (these inhibit the growth of other
bacteria)
-some strains of skin staphylococci produce antibiotics that
inhibit a wide variety of other bacteria

20. Microbiology of Food
and Milk

21. Microorganisms are intimately associated with the availability, the
abundance, and the quality of food for human consumption.
Food items are easily contaminated with microorganisms in nature,
during handling and processing.
Significance of Microorganisms in Food
1. The numbers and kinds of microorganisms present in food
reflect the quality and safety of the food
2. Some may cause food spoilage
3. Some must be kept out, removed, inhibited or killed to
Prevent spoilage of food.
4. Some can cause food poisoning or foodborne infections
5. Some can produce certain food products by fermentation
6. Some can be produced in large quatities as a food or feed
Supplement
7. Contaminating microorganisms create special problem for
Food service industry as more “ready to serve” and “fast-food”
products become available.

22. Food is particularly susceptible to microbial contamination and it serve
as a growth medium for the contaminating microorganisms
*International, federal, state, country agencies routinely inspect and
regulate food production. Standard procedures have been developed
for the microscopic and cultural examination of foods.
-Food and Agricultural Organization(FAO), World Health
Organization (WHO),United Nations International Children
Emergency Fund (UNICEF)
-Bureau of Food Administration and Drugs (BFAD)
-follows the Compendium of Methods for the Microbiological
Examination of Foods and Standard Methods for the Examination of
Dairy Products
-results from the microbiological examination of foods provide:
1. information on the quality of the raw food
2. cleanliness of the conditions under which the food was
processed

23. 3. And the effectiveness of the method of preservation
In the case of spoiled foods, it is possible:
1. to identify the microorganism responsible for the spoilage
and its source
2. as well as the conditions which permitted the spoilage to
occur. Then corrective measures can be instituted to prevent
spoilage in the future.
A. Microscopic Techniques
1. Gram stain technique
2. Breed Smear- used to make a direct microscopic count of
microorganisms in milk(the total number of microorganisms per
milliliter of milk can be calculated)
3. Howard mold-counting slide- has a chamber that holds a
measured amount of specimen.
- used to enumerate mold fragments in food products such as
fruits, juices and vegetables.(when the mold counts obtained
exceed certain limits, the product is of poor quality or has been
processed in an unsanitary manner.

24. 2. Culture techniques
a. Plate culture techniques- used to determine a specimen’s total microbial
population or to count some particular group of microorganisms
b. standard plate count- for counting bacteria in milk
Microorganisms in Fresh Foods
1. Meats- low level of surface contamination(inner tissues are sterile)
- microbial counts of 100 to 100,000 per gram surfaces of beef carcasses
- microbial counts on hamburger may reach 5 x 106 to 1 x 107 per gram of
sample
2. Poultry- freshly dressed poultry has bacterial flora on the surface(from bacteria
present on live birds and from organisms introduced during killing,
defeathering and evisceration.
-under good sanitary conditions (bacterial count is frm 100 to 1000 bacteria
per square cm of skin surface) while less sanitary, bactl count increased by
100-fold or more.
3. Eggs –inside of a freshly laid eggs is usually free of microorganisms
-cracks in the shell result in contamination and spoilage

25. Some examples of bacterial spoilage in eggs are:
a. Green rots: caused by green-pigmented Pseudomonas species that can grow at 0o C.
b. Colorless rots: Caused by species of Pseudomonas, Acinetobacter, Alcaligenes and
coliforms. Various kinds of odors may develop.
c. Black rots: caused by Proteus species which turn eggs black. Usually indicative of
storage at temperatures above recommended level
*bacteria of the genus Salmonella have periodically been a major problem, causing food
poisoning from contaminated egg products.
4. Fruits and Vegetables –occurs in various stages of development (bacteria, viruses &
fungi)
-the more tissues are invaded the greater the likelihood of spoilage
-contamination may also depend on postharvest handling used
eg. Mechanical handling(produce breaks in the tissue)
-pH of fruits are relatively low 2.3 lemons, 5.0 for bananas
-pH range for vegetable is slightly higher (pH 5.0 to 7.0) making
vegetables more susceptible than fruits to attack by bacteria
5. shellfish and Finfish- microorganisms found reflects the microbial quality of the waters
from where they harvested
-if the water is sewage polluted, the seafood is potentially capable of
transmitting pathogenic microbes
eg. Marine bacterium, Vibrio parahaemolyticus (gastroenteritis epidemics in
USA)
6. Milk- microbes contaminate via the teat canal from the outside

26. General Principles of Food Preservation
1. Asceptic Handling and Processing
2. High Temperatures
a. Boiling
-microbes from freshly drawn milk ranges between several hundred and several thousand
per milliliter. (highest in milk taken during the initial stages)
how? From the time it leaves the cow’s udder
into retail containers
Potential source of added contamination: milking equipment, the personnel, and the air in
the environment
-under sanitary conditions with strict sanitary practices produce milk with a low
bacterial count and good keeping quality
Milk -described as “most nearly perfect food”
- excellent medium for growth of microorganisms
-has great susceptibility to microbial spoilage
*Canning- 100 C for high-acid foods to 121 C for low acid foods (does not guarantee
Sterile prodts bec of spores of Clostridium botulinum (caused food poisoning)

27. B Steam under pressure
c. Pasteurization
D sterilization -300 F (148.9 C) for 1 to 2 s
3. Low temperatures
a. Refrigeration
b. freezing (-32 C)-quick freeze method (most satisfactory)
4. Dehydration
5. High osmotic pressure
a. In concentrated sugar
b. with salt brine
6. Chemical additives
a. Organic acids (benzoic, sorbic,acetic, lactic & propionic acid)
b. substances developed during processing(smoking)
c. substances contributed during microbial fermentation(acids)
7. Radiation
a. UV
b. ionizing radiation

28. Pasteurization of milk
-original time-temperature relationships determined with M. tuberculosis (regarded
as the most heat-resistant pathogen likely to occur in milk, it is destroyed when
exposed to 140 F (60 C) for 10 min.
Thus pasteurization was set to 143 F (61.6 C) for 30 min but it was discovered that
Coxiella burnetii (causative agent of Q fever transmitted by milk, can survive in milk
heated to 143 F for 30 min)
Two methods for Commercial pasteurization of milk:
1. the low-temperature holding (LTH) method or vat pasteurization
- holds the milk at 145 F (62.8 C) for 30 min
2. the high-temperature short-time (HTST) method
- exposes milk to a temperature of 161 F (71.7) for 15 sec
*after pasteurization, the finished product shld be stored at low T to retard growth of microbes
That survive pasteurization
To test if particular batch of milk has been pasteurized, phosphatase test is done.
Phosphatase –an enzyme present in raw (unheated) milk and body tissues that is
destroyed by adequate pasteurization
-by testing for the absence of this enzyme, you can determine whether milk
has been properly pasteurized
Disodium phenyl phosphatase phenol + phosphate
Phoshate
(substrate) (enzyme in raw milk) (end-products)

29. Microbial Spoilage of food
- produce changse in appearance, flavor, odor, and other qualities of food
1. Putrefaction:
Protein foods + proteolytic microbes amino acids + amines + ammonia +
hydrogen sulfide
2. Fermentation:
Carbohydrate foods + saccharolytic microbes acids + alcohols + gases
3. Rancidity:
Fatty foods + lipolytic microbes fatty acids + glycerol
Foods produced by Microorganisms
*fermented foods remains one of the most common methods of food preservation
in the world
-in production of cheese and fermented milks (starter cultures=cultures of specific
microorganisms are deliberately added to the food to initiate the fermentation)
Fermented vegetables (cabbage, cucumbers and olives)
-involves series of stages:
1. Initiation stage- microbes present on the vegetables begin to grow(aerobic, facultative

30. and anaerobic microbes. Then production of lactic acid by streptococci and lacto-
bacilli lowers the pH and inhibits further growth of undesirable Gram- and spore-
Forming bacteria.
2. Primary fermentation stage
-lactic acid bacteria and fermentative yeasts predominates (fermentation
continues)
3. Secondary fermentation
-fermentative yeasts which are acid-tolerant, utilize any residual fermentable
carbohydrate
4. Postfermentation stage
- microbial growth, particularly molds and oxidative yeasts may occur on
surface of the fermented product
Fermented Dairy Products
-microorganisms play the key role in producing a product with a desirable
flavor, aroma and physical appearance
a. Fermented milks – fermented foods made from milk such as sour cream and
yogurt (lactic acid bacteria are the most commonly used starter cultures for the prepn of
these foods)
1. addition of starter culture to pasteurized milk
2. incubation at a T favorable for the growth of starter culture microorganisms

31. 3. The principal product is lactic acid along with diacyl(lesser amnts of buttery-
Flavored cpd)
Production of Cheese
-bacteria convert curd (casein in milk) into the desired cheese
Manufacture of cheese includes the following steps:
1. curd is separated from whey (liquid portion of curdled milk)
-precipitation of the casein is caused by addition of the enzyme
rennin to the milk or by lactic acid produced when milk undergoes lactic acid
Fermentation
2. adjustments are made to the curd
-adding salt
-removing a specific amount of moisture
-inoculating with a particular microorganism if required
-shaping the curd into a desired size and form
3. incubation of the curd under conditions which favor the growth of the
desired microorganisms
Two types:
1. Unripened cheeses-curd which has not been fermented by microorganisms
Eg. Cottage and cream cheese

32. 2. Ripened cheeses
-result from the growth of bacteria or molds in or on the curd during a
prescribed incubation period
-may be classified as:
a. Hard
b. semi-soft
c. soft
Microbial Cells as Food-Single Cell Protein (SCP)
-cells of bacteria, yeasts and algae produced in massive quantities can
be used as food for animals as well as for humans
-attractive as food sources bec they can be grown on industrial wastes
or by-products and yield a large crop that is rich in protein(called single-cell
protein)= can be used as food substitute or supplement

33. Microbiology of Water

34. Drinking water of most communities and municipalities comes from surface
sources-rivers, streams and lakes
Water can be perfectly clear, odorless and tasteless and yet be unsafe to drink.
Contaminants that pollute water are classified into three categories:
1. chemical
2. physical
3. biological
Water maybe:
a. Potable – water that is safe to drink is free of disease-producing
microorganisms and chemical substances harmful to health
b. Non-potable-must be purified before it can be used for human con-
sumption
-purification method vary depending on the source of water and amount
of water needed