1. Suggestion of food microbiology-5005
Chapter: 02
Exam Date:15/11/2013
1. Write down the name of factors affecting the Growth of Micro-Organisms.
Factors Effecting the Growth of Micro-Organisms
Intrinsic Factors or the compositional factors of a food affecting microbial growth
• PH
• Moisture Content
• Water activity
• Oxidation-reduction potential
• Physical structure of the food
• Available nutrients
• Presence of antimicrobial agents
Extrinsic factors
• Temperature
• Relative humidity/moisture
• Carbon dioxide or oxygen
• Types and numbers of Microorganisms in the food
2. How pH effect on the Growth of Micro-Organisms.
pH effect: Every microorganism has a minimal, a maximum and an optimal pH for growth.
Microbial cells are significantly affected by the pH because the apparently have no mechanism for adjusting
their internal pH. In general, yeasts and molds are more acid tolerant than bacteria.
Foods with low pH values (below 4.5) usually are not readily spoiled by bacteria and are more susceptible
to spoilage by yeasts and molds.
Molds and Yeasts: Both are acidic pH favors them. They both can grow in a pH range of 2 to 8.
Bacteria: A pH near neutrality (pH 7.0) favors their growth
3. What is water activity? The effect of water activity on the Growth of Micro-Organisms.
Water activity (aw):
Microorganisms have an absolute demand for water. Without water no growth can occur. The exact amount
of water needed for growth of microorganisms varies. This water requirement is best expressed in terms of
available water or water activity aw.
aw = water activity = vapor pressure of food/ vapor pressure of water
aw of pure water is 1.00. Equilibrium relative humidity=aw×100. (aw below 0.70 greatly reduces microbial
growth)
Most bacteria grow at aw 0.85-1.0. Also they prefer foods with high water level.aw around 0.90.
Bacteria need more water than molds and yeasts to survive.
Mold: They can grow in low water level.(aw 0.62-0.92). Many molds are somatically tolerant and can grow at
a aw value of 0.6.
Yeasts: They prefer high water foods.( aw 0.62-0.92)
4. Classification of Micro-organism on Temperature and Oxygen
Temperature
Micro-organisms can be categorized into one of four groups depending on their optimum growth
temperature and the temperature range at which they will grow.
i) Thermophiles: Have optimum growth ca. 55 °C and a growth range of 30 - 75 °C
ii) Mesophiles: Have optimum growth ca. 35 °C and a growth range of 10 - 45 °C
iii) Psychrotrophiles: Have optimum growth ca. 20 - 30 °C and a growth range of 0 - 40 °C
Ability to use free oxygen microorganism have been classified as-
I. Aerobic- When they require free oxygen.eg. Molds are aerobic & Some bacteria are (Acetobacter)
II. An -aerobic- When they grow best in the absence of free oxygen.eg. Some bacteria are (clostridium).
III. Facultative- When they grow well either aerobically or an-aerobically.
IV. Facultative anaerobes-whey will grow in the presence or absence of oxygen eg.Yeast and some bacteria
are (bacillus).

2. 5. How dose Salt/Sugar Concentrations effect on water activity of the Growth of Micro-Organisms.
Salt/Sugar Concentrations
Most microbes cannot survive environments in which there are such high concentrations of salt or sugar.
Certain foods have long been preserved from spoilage by adding lots of salt and sugar to them. Salt and
sugar tie up the water effectively reducing the aw; salt cured ham and candied fruits are examples

3. Chapter: 03
Topic: Source and stages of microbial contamination of food.
1. #. Q. What are the Sources of microbial contamination of food?
Microorganisms are present in natural ecosystems such as air, soil and water.
They are also present on the man himself and all living animals and plants.
Therefore, all processed foods can be contaminated by microorganisms.
Eight environmental sources of microorganism found in food are given bellow-
1. Soil & water 2. Plants & plants products 3. Food utensils 4. Intestinal tract of human & animals 5. Food
handlers 6. Animal feeds 7. Animal hides 8. Air & dust
2. #. Q. Basic criteria for assurance of fitness of food?
Fitness of food:
Fitness of food will depend on person’s judgment, for what one person will eat another will not.
Some criteria for assurance of fitness:
a) The desired stage of development of maturity: Fruits should be at a certain but differing stage of
ripeness; sweet corn should be young enough to be tender and milky
b) Freedom from pollution at any stage in production or handling: Vegetables should be consumed raw if
they had been fertilized with sewage; oysters from waters contaminated with sewage should be rejected;
food handled by dirty or diseased workers should be spurned.
c) Freedom from objectionable change resulting from microbial attack or action of enzymes of the
food: Microorganisms can grow in food and can make changes which make food undesirable to accept or
consumes
3. #. Q What is spoilage? Cause of spoilage
When a food unfit for eat to sanitary reasons usually it is called spoilage.
Following cause of spoilage
a) Growth and activity of microorganisms
b) Insects
c) Action of the enzymes of the plant and animal food.
d) Purely chemical reactions. ( those not catalyzed by enzymes of the tissues or of microorganisms)
e) Physical changes, such as those caused by freezing, burning, drying, pressure etc.
4. # Q. Classification of foods by ease of spoilage
On the basis of spoilage, foods can be placed in three groups:
a. Stable or nonperishable foods: These foods, which do not spoil unless handled carelessly, include such
products as sugar, flour and dry bean.
b. Semi perishable foods: If these foods are properly handled and stored, they will remain unspoiled for a
fairly long period, e.g. potatoes, some varieties of apples, waxed rutabagas and nutmeats.
c. Perishable foods: This group includes most important daily foods that spoil readily unless special
preservative methods are used. Meats, fish, poultry, most fruits and vegetables eggs and milk belong in this
classification.

4. Chapter: 04
Topics on: Chemical changes caused by microorganisms in foods
1. Why Meat & Fish are ideal culture media?
MEAT: Meat is an ideal culture medium for many organisms because it is high in moisture, rich in
nitrogenous foods and plentifully supplied with minerals and accessory growth factors. Also, it usually has
some fermentable carbohydrate (glycogen) and is at a favorable PH
(5.7-7.2) for most microorganisms.
Problem Food Chemical Cause Organisms Involved
Rancidity Meat Fat Pseudomonas,yeast
Decomposition/hydrolysis Meat Fat Mucor
FISH: Like meat, fish is also an ideal culture medium and may spoiled by autolysis, oxidation or bacterial
activity because it is high in moisture, rich in nitrogenous foods and plentifully supplied with minerals and
accessory growth factors. Also, it usually has some fermentable carbohydrate (glycogen) and is at a
favorable PH
(5.7-7.2) for most microorganisms. Fish is more perishable than meat because of more rapid
autolysis
Problem Food Chemical Cause Organisms Involved
Slime Fish Polysacharide Pseudomonas
H2S/Mercaptans Fish Non protein nitrogen Pseudomonas
2. Why Milk is the excellent culture media?
Milk is an excellent culture medium for many kinds of microorganisms, being high in moisture, neutral in pH
(7.0 ) and rich in microbial foods.
Problem Food Chemical Cause Organisms Involved
Ropiness Milk Polysaccharides Alcaligenes,
Brown Milk Milk Tyrosine (oxidation) Pseudomonas
3. What is fermentation? Ropiness of Bread and milk
Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a
sugar, into an alcohol or an acid.
For example, yeast performs fermentation to obtain energy by converting sugar into alcohol. Bacteria
perform fermentation, converting carbohydrates into lactic acid.
Ropiness is a defect in food caused by the growth of undesirable bacteria. It is usually characterized by
stringiness, increased viscosity or sliminess.
Product Name Chemical cause Microorganism
Ropiness of Bread Gluten, Polysaccharides Alcaligenes, Bacillus
Ropiness of Milk Polysaccharides Alcaligenes,
4. Which chemicals are changes in cereal?
Chemical change in cereal grains and meals:
Cereals contain sugar and nitrogen compounds, minerals and accessory growth substances.
If moisture level of whole grain contain low (below 11% moisture) than the spoilage by microorganisms is
inhibited but if they are moistened then growth of microorganisms is accelerated.
Wet meals will undergo an acid fermentation, chiefly by the lactic acid and Coliform bacteria. This may be
followed by an alcoholic fermentation by yeasts. Finally mold and yeast will grow on the top surface.
Main chemical change occurs in cereal and cereals products cause by fermentation.
Cereals:
Problem Product Chemical cause Microorganism
Sour Grain, meal,
Bread
Polysaccharides Acetobacter, Lactobacillus,Coliform
Sticky dough Bread Gluten Proteolytic bacteria
Mustiness Bread, Cake Chloroanisoles Moulds
Ropiness Bread Gluten,Polysaccharides Alcaligenes,.Bacillus
Slime Confectionery Polysaccharide Pseudomonas,Leuconostoc, Bacillus

5. 5. Which chemicals are changes in Milk?
Milk products: Milk and cream, butter, cheese, condensed and dried milk products etc.
Milk is an excellent culture medium for many kinds of microorganisms, being high in moisture, neutral in pH
(7.0) and rich in microbial foods.
Contamination:
Milk contamination of manure, soil and water and also from utensils
Microorganism: Bacteria: Enterococcus, Micrococcus, Bacillus,Sarcina, Serratia etc.
Problem Product Chemical cause Microorganism
Souring Milk, Cheese Acids: acetic, lactic, citric,
butyric
Lactic acid bacteria Bacillus
Butyric acid bacteria Acetobacter
Ropiness Milk Polysaccharides Alcaligenes,
Holes Hard cheese (gas production) Coliforms
Curdling Milk Acid production Lactic acid bacteria
Gas Milk Carbohydrate Lactobacillus,Clostridium
Proteolysis Milk Protein Yeast/mold, lactic acid bacteria
Bitter flavor Milk Lactose (fermentation) Coliform,Yeasts
Brown Milk Milk Tyrosine (oxidation) Pseudomonas
6. Why an whole made on heart cheese.

6. Chapter: 05
1. Classified Bacteria based on structure, metabolism and temperature sensitivity.
Bacteria can have three basic shapes
1. Cocci – sphere-shaped
• Plural is Cocci.
• Spherical bacterium
• Single cells - Monococci
• Pairs - Diplococci
• Chains - Streptococci
2. Bacilli – rod-shaped
• Plural is bacilli.
• A rod - shaped bacterium.
• Exists as single cells, in pairs
(diplobacilli), and
in chains (streptobacilli)
3. Spirilla – spiral-shaped
• Plural is Spirilli
• A spiral - Shaped bacterium.
• Exist only as single cells.
Modes of Nutrition/metabolism:
Bacterial Physiology-Nutritional Needs
The two categories are,
1. Heterotrophic Bacteria
Heterotrophs must get their food from a source of pre-formed organic matter:
 Saprobes – feed on dead organic matter
 Parasites – feed on a host cell-Example, Mycobacterium tuberculosis
 Photoautotroph – use sunlight to make food
 Chemoautotroph – oxidize inorganic matter such as iron or sulfur to make food
2. Autotrophic Bacteria
 Autotrophs- can make their own food:
 Photosynthetic-use a special type of chlorophyll called bacteriochlorophyll.
O2 is not released in bacterial photosynthesis
 Chemosynthetic -obtain energy by breaking down inorganic material such as iron or sulfur.
Bacteria are classified based on temperature are as follows:
Mesophiles : Those bacteria grow best at ambient temperature (20°C to 40°C)
Thermophiles : Those have an optimum temperature above 450
C
Psychrophiles : Grow best from about at 0-150
C
Extremophiles : Grow well at 100-1200
C
2. Distinguished Bacteria and Virus.
SL Characteristics Bacteria Virus
01 Number of cells: Unicellular; one cell No cells; not living
02 Organism Living organisms Not living
03 Cell Prokaryotic cells Not made of cells
04 Survivability are always alive dead or alive in living cell
05 Reproduction Can replicate on its own Requires a host cell to replicate
06 Treatment Can be treated with antibiotics Can be prevented with vaccine
07 Genetic materials DNA DNA or RNA.
08 Enzymes Yes Yes, in some
09 Infection Localized Systemic
10 Visible Visible under Light Microscope Visible only under Electron Microscope
11 Size Larger (1000nm) Smaller (20 - 400nm)

7. 3. Distinguished Yeast and Molds.
Yeasts-“fungi, unicellular, asexual reproduction through budding, colorless parasite
Molds- fungi, multi-cellular, sexual& asexual reproduction, colorful parasite
4. Distinguished Bacteria & Fungi.
Bacteria Fungi
Bacteria are prokaryotes Fungi are eukaryotes
Bacteria are single celled Fungi are multi-cellular except for yeast
Bacteria can be autotrophy or heterotrophy Fungi are heterotrophy
Bacteria have 3 distinct shapes Fungi have various shapes.
Bacteria reproduce sexually via binary fusion Fungi are capable of reproducing both sexually or asexually.
5. Explain the growth curve of Bacteria.
The growth curve of Bacteria: In studies, bacterial growth four different phases
Fig. Bacterial Growth Curve
1. Lag phase: During the lag phase of the bacterial growth cycle, synthesis of RNA, enzymes and other
molecules occurs.
2. Growth phase/ exponential phase is a period characterized by cell doubling. The number of new bacteria
appearing per unit time is proportional to the present population. For this type of exponential growth, plotting
the natural logarithm of cell number against time produces a straight line. The actual rate of this growth (i.e.
the slope of the line in the figure) depends upon the growth conditions, which affect the frequency of cell
division events and the probability of both daughter cells surviving.
3. Stationary phase: Stationary phase results from a situation in which growth rate and death rate are equal.
The number of new cells created is limited by the growth factor and as a result the rate of cell growth
matches the rate of cell death. The result is a “smooth,” horizontal linear part of the curve during the
stationary phase.
4. Death phase, bacteria run out of nutrients and die.

8. 6. Write name of some virus and disease produced by them.
SL# Name of Virus Name of Disease
Virus that affect Animal
1 Human immune deficiency virus Acquired Immune Deficiency Syndrome (AIDS)
2 Corona virus - common cold
3 Onco viruses Cancer
4 Hepatitis C viruses Hepatitis
5 Marburg virus, Ebola virus hemorrhagic fever
6 Rabies virus Rabies
7 Mumps virus Virus
8 Influenza viruses, types A, B, C Influenza
9 Yellow fever virus causes yellow fever,
10 Poliovirus Polio
11 Foot and Mouth Disease virus Foot and Mouth Disease
Virus that affect Plant
01 Rice tungro bacilliform virus (RTBV) Tungro
02 Wheat draft virus (WDV) Wheat draft
03 Jute Mosaic Virus (JMV) Chlorosis
04 Papaya Mosaic Virus (PMV) Yellow Mosaic
05 Potato Leaf Curl Virus (PLCV) Leaf Curl
06 Bunchy Top Virus (BTV) Bunchy Top
07 Potato Leaf Roll Virus (PLRV) Leaf Roll
7. Example of Round shape and Rod Shape Virus.
Rod shape Virus: tobacco mosaic disease virus, potato mosaic disease virus, turnip yellows mosaic virus
Round shape Virus: Influenza virus
8. What is mycosis? Illustrate different types of mycosis inhuman.
Mycosis: Mycosis is a fungal infection of animals, including humans. A variety of environmental and
physiological conditions can contribute to the development of fungal diseases. Inhalation of fungal spores or
localized colonization of the skin may initiate persistent infections; therefore, mycoses often start in the
lungs or on the skin
Types of mycoses:
1. Superficial mycoses: In superficial mycoses infection is localized to the skin, the hair, and the nails such
as ringworm. Candida albicans is yeast causing candidiasis or "thrush" in humans as superficial mycoses,
candidiasis typically infects the mouth or vagina is part of the normal flora of the vagina and gastrointestinal
tract and is termed a "commensal.
2. Cutaneous: Mycosis or darmatomycosis include such infections as athlete’s foot and ringworm, where
growth occurs only in the superficial layers of skin, nails or hair.
3. Subcutaneous mycoses: These are infections confined to the dermis, subcutaneous tissue or adjacent
structures. Infection may arise following the wounding of the skin and the introduction of vegetable matter.
Infection usually follows and insect bite, thorn pricks or scratches from a fish spine.
4. Systemic mycoses: These are invasive infections of the internal organs with the organism gaining entry by
the lungs, gastrointestinal tract or through intravenous lines.
They may be caused by: (i) primary pathogenic fungi or (ii) by opportunistic fungi that are of marginal
pathogenicity
Examples include histoplasmosis, blastomycosis, coccidiomycosis and paracoccidiodomycosis.

9. 9. What do you mean by staining? Explaining about Gram Staining Procedure.
Staining:
Staining is used in microscopy to enhance contrast in the microscopic image. Stains may be used to define
and examine bulk tissues, cell populations (classifying different blood cells, for instance), or organelles
within individual cells.
The Gram Staining Procedure:
Equipment: Bunsen burner, alcohol-cleaned microscope slide, water
Reagents: Crystal violet, Gram's iodine solution, acetone/ethanol (50:50 v:v), 0.1% basic fuchsine solution
Procedures:
1. Prepare a Slide Smear:
A. Transfer a drop of the suspended culture to be examined on a slide with an inoculation loop. If staining a
clinical specimen, smear a very thin layer onto the slide, using a wooden stick. The smear should be thin
enough to dry completely within a few seconds.
B. Spread the culture with an inoculation loop to an even thin film over a circle of 1.5 cm in diameter. Thus,
a typical slide can simultaneously accommodate 3 to 4 small smears if more than one culture is to be
examined.
C. Air-dry the culture and fix it or over a gentle flame, e.g. taking the slide in and out of the flame.
2. Gram Staining:
A. Add crystal violet stain over the fixed culture. Let stand for 10 to 60 seconds; Note that the objective of
this step is to wash off the stain, not the fixed culture.
B. Add the iodine solution on the smear, enough to cover the fixed culture. Let stand for 10 to 60 seconds
and rinse the slide with running water. Shake off the excess water from the surface.
C. Add a few drops of decolorizer. Rinse it off with water after 5 seconds.
D. Counter stain with basic fuchsine solution for 40 to 60 seconds. Alternatively, the slide may shake to
remove most of the water and air-dried.
3. Quality control:
This should be smeared into a drop of clean tap water on a clean glass slide.
4. Examine the finished slide under a microscope.
Filamentous and pleomorphic forms may be observed among the Gram (-) rod species.
Gram reaction of the organism may also change after antimicrobial therapy, Gram (+) bacterial may
become gram variable.
10. Draw an ideal bacterial cell and indicated its different parts.

10. 11. Why Agar use in cultural media
12. What is selective and indicator media?
13. What is food born infection and food intoxication

11. Chapter: 06
1. Why estimating the number of microorganism?
2. Why aseptic collection of sample for microorganism
3. What is direct Microscopic count? Value of DMC
4. Principal of electric particle count.
5. Compare between Pour plating and spread plating technique
6. Discus membrane filters techniques. Advantage and disadvantage of membrane filters techniques
7. Define reductase .Indicate several procedure that can be estimate the number of viable microorganism.
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