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1. Kwame Nkrumah University of
Science & Technology, Kumasi, Ghana
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Biology for Mathematics
MICROBIOLOGY
Dr. (Mrs.) Sandra Abankwa Kwarteng
Department Theoretical and Applied Biology
College of Science
BIOL 181

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Course Objectives
 Introduction to the science of microbiology.
 Nature and kinds of microorganisms.
 Nutrition and growth of microorganisms.
 Growth kinetics.
 Epidemiology-principles and methods.

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Introduction to the Science of Microbiology
 Microbiology is the study of microorganisms.
 Microorganisms are minute living creatures that
individually are too small to be seen with the naked eye.
 Microorganisms are found everywhere in our
environment; air, soil, water.
 Majority of microbes do not cause disease (non-
pathogenic).
 Instead they are used to promote our well-being serving
as source of food and medicine.

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Various branches of microbiology:
 Medical microbiology
 Study of the pathogenic microbes and the role of
microbes in human illness.
 Food microbiology
 Study of microorganisms relevant for food production,
food spoilage and foodborne illness.
 Agricultural microbiology
 Study of agricultural relevant microorganisms.
 Pure microbiology
 Study of microorganisms on a theoretical level.
Introduction to the Science of Microbiology

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Nature and Kinds of Microbes
 Microorganisms include:
 Viruses
 Bacteria
 Fungi
 Protozoa
 Cyanobacteria
 Archaea
 Algae

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Nature and Kinds of Microbes
 Microbes can either produce more of itself to cause
diseases or produce chemicals (usually called
toxins) to interfere with the normal processes of its
host.
Virus: Poliomyelitis, AIDS, Hepatitis, Influenza, COVID-19.

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Bacteria:
Fungi:
Protozoa:
Cyanobacteria:
Diphtheria, Cholera, Typhoid, Tuberculosis, Leprosy.
Athlete’s foot, Ringworm, Candidiasis.
Malaria, Cryptosporidiosis, Giardiasis.
Swimmers allergies, nephritis.
Nature and Kinds of Microbes

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Nature and Kinds of Microbes
 Some cell structures can be involved
in the cause of disease, example:
 Flagella  for swimming motility
 Pili /fimbriae  for attachment or
adherence to surfaces
Can recognize and
stick to cells
(adhesions) capsules
and also prevent
phagocytosis

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Nature and Kinds of Microbes
Based on cell structure
Some of these differences are
exploited as targets for
antibiotics e.g. the cell wall of
bacteria.

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Nature and Kinds of Microbes
 Bacteria are prokaryotes
and are differentiated based
on:
 Morphology (shape)
 Nutritional requirements
 Chemical composition
(staining reactions)
 Biochemical activities
and some source of
energy (sunlight and
chemicals)

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Morphological
 The forms of bacteria include:
 Spherical or round forms called
coccus .
 Rod-shaped forms called
bacillus
 Spiral forms or spirillum
 Corkscrew form
 Club rod form called fusiform
 Coma form called vibrio
 Coccibacillus is neither rod-shaped nor spherical but in
between
 Filamentous long threads called fusobacterium

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(a, b) Chain- cell divides in one
plane
(c,d) Packets- cell divides in
two or more planes
perpendicular to one another
(e) Cluster-cell divides in
several planes at random
Morphological
 The forms of bacteria

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The arrangements of bacteria include:
Cocci that divide and remain in pairs after dividing
called diplococcus
Those that divide and remain attached in chainlike
patterns are streptococcus
Those that divide in multiple planes and form a grape-
like cluster staphylococcus
Morphological

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 Those that divide in two planes and remain in groups
of four are tetrads.
 Those that divide in three planes and remain attached
in cube-like groups of eight are called sarcina.
Morphological
S

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 Bacilli divide only
across their short axis,
so there are fewer
groups of bacilli than
are coccus.
Morphological

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Morphological
 Spirochetes move by means of an
axial filament, which resembles a
flagellum but is contained under
an external flexible sheath.
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 Spirals which are helical and
flexible are called spirochetes.
 Rigid spirals are called spirillum.
 Spirilla use whip-like external
appendages called flagella to move.

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 Generally bacterial shape is determined by heredity.
 Most bacteria are monomorphic that is they maintain a
single shape.
Morphological
 However, a number
of environmental
conditions can alter
that shape.
 If the shape is altered,
the identification
becomes difficult.

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Nutrition and Growth
 Every organism must find in its environment all of the
substances required for energy generation.
 These chemicals and elements of this environment that
are utilized for bacterial growth are referred to as
nutrients.
 In the laboratory, bacteria are grown in/on culture
media/medium which are designed to provide all the
essential nutrients in solution for bacterial growth.

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Nutrition and Growth
 Bacteria are ubiquitous. They exhibit a wide range of
tolerance to the environment.
 Obtain energy from an amazing variety of substrates.
 They show the most extreme forms of metabolism for
any given environmental factor.
 For e.g. they can be classified based on their
 oxygen requirements
 carbon source
 participation in the nitrogen cycle
 temperature tolerance

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Classified based on Oxygen Requirements
 Aerobic:
 Require oxygen to grow, eg Staphylococcus species.
 Anaerobic:
 Do not require oxygen to grow, eg Clostridium.
 Microaerophilic:
 Require very little oxygen to grow, eg Campylobacter.
 Obligate aerobes:
 Grow only in the presence of oxygen, eg Pseudomonas.

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Oxygen Requirements
 Facultative anaerobes (or
facultative aerobes) : eg Yeast
 They are organisms that can
switch between aerobic and
anaerobic types of
metabolism.
 Obligate anaerobes: eg Clostridium
 Do not need nor use oxygen to grow. In fact, oxygen is toxic
to it, as it either kills or inhibits their growth.
 Obligate anaerobic live by fermentation/anaerobic respiration.
 Under anaerobic conditions they grow by fermentation or
anaerobic respiration. But in the presence of O2 they
switch to aerobic respiration.

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Oxygen Requirements
 They are insensitive to the presence
of O2
 They live by fermentation alone
whether or not O2 is present in their
environment e.g. lactic acid bacteria
 Aerotolerant anaerobes: eg. Propionibacterium acnes
 They are bacteria with an exclusively anaerobic
(fermentative) type of metabolism
 Microaerophile is a microorganism that requires O2
to survive, but requires environments containing lower
levels of oxygen than that present in the atmosphere.
Example is the Helicobacter pylori

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Classified based on Carbon Requirements
 Phototroph uses energy from sunlight to synthesize
organic compounds for nutrition. Eg. Algae
 Chemotrophs obtain their energy through chemical
reactions. Eg. Nitrosomonas
 Lithotrophs - derive energy from oxidation of
inorganic substances. Eg. Cyanobacteria
 Organotrophs - derive energy from oxidation of
organic substances. Eg. Fungi

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 Autotrophs are organisms that can produce their
own food, using materials from inorganic sources,
eg. Algae
 Photoautotrophs use energy from sunlight to convert
carbon dioxide and water into organic materials to
be used in cellular functions eg. Cyanobacteria
 Photoheterotroph obtain their energy from sunlight
and carbon from organic material and not carbon
dioxide, eg. Heliobacteria.
Carbon Requirements

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Carbon Requirements
 Heterotroph is an organism that depends on organic matter
already produced by other organisms for its nourishment
eg Fungi.
 Chemoautotrophs/chemolithotroph are able to synthesize
their own organic molecules from the fixation of carbon
dioxide. The energy required for this process comes from
the oxidation of inorganic molecules, eg Nitrosomonas
 Chemoheterotroph unlike chemoautotrophs, they are
unable to synthesize their own organic molecules. They
must ingest preformed carbon molecules, such as
carbohydrates and lipids. Eg. Cladosporium

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Nitrogen Requirements
 Nitrogen Cycle is a biogeochemical process through
which nitrogen is converted into many forms,
consecutively passing from the atmosphere to the soil to
organism and back into the atmosphere

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 Nitrogen fixation is the initial step of the nitrogen
cycle. Here, atmospheric nitrogen (N2) which is
primarily available in an inert form, is converted
into the usable form -ammonia (NH3).
 Nitrification is the process by which ammonia is
converted to nitrites (NO2) and then nitrates
(NO3).
 Denitrification is the process in which
the nitrogen compounds makes its way back into
the atmosphere by converting nitrate (NO3) into
gaseous nitrogen (N)
Nitrogen Requirements

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 Psychrophile (psychrophilic) grow in cold temperatures
 Optimal growth at 15o to 20oC
 Examples, Proteus
 Mesophile (mesophilic) grow in moderate temperatures
 Optimal growth at 20o to 45oC, eg. Listeria
Classified based on Temperature Requirements
 Thermophile
(thermophilic) grow in
elevated temperatures
 Optimal growth at
50o to 70oC, eg
Archaea

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Kinetics of Growth
 Under ideal conditions, e.g. laboratory conditions,
where the microbes experience uniform and optimum
chemical and physical conditions, the population change
in a perfectly regular and predictable manner. Most
bacteria multiply by binary fission.
 In the laboratory, under favorable conditions, a growing
bacterial population doubles at regular intervals.
 Growth is by geometric progression: 1, 2, 4, 8, etc. or
20, 21, 22, 23....2n (where n = the number of generations).
 This is called exponential growth.

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Generation Time
 Generation Time is the time required for a cell to divide or its
population to double.
 It varies from one organism to the other. For example that for E.
coli is 20 minutes
 For microbes to grow, they require appropriate media.
Depending on the type of microbe, different media are required.
 Therefore generation time is G=t/n
 G (generation time) =t(time, in minutes or hours)/n(number of
generations)
 If we start with one cell, when it divides, there are 2 cells in the
first generation, 4 cells in the second generation, 8 cells in the
third generation, and so on. The generation time is the time
interval required for the cells (or population) to divide.

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Growth curve

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Growth curve

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Lag phase
 On transfer to a new medium there is a period of
adjustment, the length of which depends on the bacterium’s
closeness of the medium in which the bacteria had been
growing to that into which it has been inoculated.
 The size of the inoculum relative to the volume of medium
also contribute to the lag phase.
 The main cause of the delay however is the time taken for
appropriate enzymes to be induced. There are two main
types of enzyme:
 Inducible enzymes - are produced only when the substrate is
present
 Constitutive are produced all the time.
Growth curve

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Log phase:
 During log phase bacteria grow and divide at a constant rate.
 After a while growth will slow down due to overcrowding,
build up of toxic products and starvation.

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Stationary phase
 Number of cells dividing and dying is in equilibrium
 Nutrient supplies are depleted
 Toxic waste products accumulate and a steady state in cell
numbers is reached.
 Passage through stationary phase prepares bacteria for
survival in unfavorable conditions

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Death and declining phase:
 Net decrease in numbers as more cells die than are replaced
by new cells
Survival Phase
 There are two main types of enzyme:
 Inducible enzymes - are produced only when the substrate
is present
 Constitutive are produced all the time.

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Epidemiology
 The study of the distribution and determinants of health-
related states/diseases or events in specified populations,
and the application of this study to control health problems.
 It is concerned with the frequencies and types of illnesses
and injuries among groups of people and with the factors that
influence their distribution.
 A disease is an abnormal condition affecting the body of an
organism. It is often construed to be a medical condition
associated with specific symptoms and signs.
 Diseases may be caused by external factors, such as that as
seen in infectious disease, or it may be caused by internal
dysfunctions, such as autoimmune diseases.

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Scope of epidemiology
1. Causation of the
disease.
2. Natural history of the
disease.
3. Health status of the
population.
4. Evaluation of
Interventions.

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Causation of the disease
 Most of diseases are caused by interaction between
genetic and environmental factors (Diabetes) with
personal behaviors affecting this interplay.
 Epidemiology is used to study their influence and the
effects of preventive interventions through health
promotion.

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Natural history of the disease
 Epidemiology is also concerned with
the course and outcome (natural
history) of diseases in individuals
and groups.

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Health status of the population
 Epidemiology is often used to describe the health
status of population.
 Knowledge of the disease burden in populations is
essential for health authorities and all other
stakeholders to use limited resources to the best
possible effect by identifying priority health
programmes for prevention and care.

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Evaluation of Interventions
 To evaluate the effectiveness and efficiency of health
services.
 This means determining things such as –
 Impact of contraceptive use on population control.
 The efficiency of
sanitation
measures to
control d
iarrheal
diseases
 The impact of COVID-
19 vaccines

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Epidemiological Terms

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Epidemiological Terms
Incidence and Prevalence
 These are fundamentally different ways of measuring
disease frequency.
 The incidence of disease represents the rate of
occurrence of new cases arising in a given period in a
specified population, while
 The prevalence is the
number of existing cases
(old+ new) in a defined
population at a given point
in time.

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Uses of prevalence rates
 Understand magnitude of current health problems
in a population.
 Compare magnitude of various health problems to
set priorities.
 Assessing the need for health care and the planning
of health services.
 All the above are not limited to burden in terms of
monetary costs; it also reflects burden in terms of
life expectancy, morbidity, quality of life, or other
indicators

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Therefore
prevalence is
best used for:
Chronic,
long-term
illness
Monitoring
of changes
in chronic
diseases

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Specialized incidence measures
Uses of incidence rate
 Morbidity rate
 Mortality rate
 Attack rate:
 It is a variant of an
incidence rate, applied to a
narrowly defined
population observed for a
limited time, such as
during an epidemic.
 The attack rate is usually expressed as % percent.

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Factors affecting incidence rate
 New risk factor
 Food additives and cancer
 Changing habits
 Increased smoking and development of lung cancer
 Changes in virulence of causative organisms
 Drug-resistant bacteria (TB).
 New variant of SARS-CoV-2 ‘more virulent’.
 Changes from intervention programs.
 Vaccination against measles incidence of
measles.

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 Selective migration of susceptible persons to an endemic
area incidence
 Population pattern
 Aging incidence of Degenerative diseases
Incidence is
best used for:
Short-term,
acute illness
Monitoring of
epidemic
illness
Factors affecting incidence rate
Reporting
Increased reporting incidence
Screening
Early detection of cases incidence
New diagnostic tools
New diagnostic tools detection of
cases

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 The two key elements measured in most
epidemiological studies are the exposure and the
outcome.
 Exposure
 It is the process by which an agent comes into
contact with a person or animal in such a way that
the person or animal may develop the relevant
outcome, such as a disease.
 Outcome
 It is the disease, or event, or health related state,
that one are interested in
Epidemiological Terms

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Types of Epidemiological studies
1. Observational Studies
 Observational studies allow nature to take its course.
 The investigator measures but does not intervene.
 Descriptive Study
 It is often the first step in an epidemiological and
limited to a description of the occurrence of a disease
in a population. It is for formulation of hypothesis.
 Analytic Studies
 It involves analyzing relationships between health
status and other variables. It is for testing of
hypothesis.

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2. Experimental Studies
 Experimental Studies involves testing the
effect of interventions or services on disease
Types of Epidemiological studies

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Types of Epidemiological studies

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Importance of Epidemiology
 Allows greater knowledge of community and its
problems
 To search for causes of ill-health
 Assist in putting priorities for action
 For planning and evaluation of the effectiveness and
efficiency of health services e.g. the value of treating
high blood pressure, the efficiency of sanitation
measures to control diarrheal diseases etc.