Ch 6 Microbial growth
I. Introduction to Microbial Growth
A. Define microbial growth. –
 Refers to increase in cell number and not cell size. Cell division leads to the
growth in cell numbers. Bacteria grow and divide by binary fission.
B. Explain how microorganisms reproduce and increase in number. –
 Bacteria grow and divide by binary fission in a rapid and relatively simple
process.
II. Factors Affecting Microbial Growth
A. Temperature – Microbes are loosely classified into several groups based on
their preferred temperature ranges.
1. Define psychrophiles, mesophiles, and thermophiles. Know the location and
significance of each group and explain the temperature range for each group.
 Psychrophiles – “Cold-Loving”. Can grow at 0°C.
o True Psychrophiles – grow in extreme cold conditions. Sensitive to
temperatures over 20°C. Optimum growth at 15°C or below.
 Location – North Pole, oceans depths.
 Significance – rarely causes disease or food spoilage.
o Psychrophiles – Optimum growth at 20°C to 30°C
 Location – Refrigerator
 Significance – Causes food spoilage.
 Mesophiles – “Middle Loving” (Most bacteria, pathogens, and common
spoilage organisms).
o Location – many have adapted to live in the bodies of animals.
o Significance – best growth between 25 °C to 40°C with an optimum
temperature commonly at 37°C
 Thermophiles – “Heat Loving”. Some thermophiles form extremely heat
resistant endospores. Optimum growth between 50°C to 60°C. Many cannot
grow below 45°C.
o Location – sunlit soil, compost piles, and hot springs.
o Significance – do not cause disease.
o Extreme Thermophiles (Hyperthermophiles) – Optimum growth at
80°C or higher.
 Location: Found in archaebacteria and most live in volcanic and
ocean vents.
3. Discuss the impact of temperature on microbial growth.
B. pH
1. Describe the concept of pH and its scale.

2. Explain acidophiles and alkaliphiles. Know the significance of each group.
3. Discuss the optimal pH range for most microorganisms.
C. Water Availability (Water Activity)
1. Define osmotic pressure . (High salt and High sugar conc)
2. Explain how water availability affects microbial growth.
3. Discuss halophiles and their adaptations.
D. Oxygen Availability
1. Describe different oxygen requirements of microorganisms (aerobes,
anaerobes, facultative anaerobes, microaerophiles).
E. Chemical Requirements
1. Explain the essential nutrients required for microbial growth (carbon,
nitrogen, sulfur, phosphorus, and trace elements and oxygen). Know the
functions for each element.
III. Phases of Microbial Growth
A. Lag Phase
1. Describe the characteristics of the lag phase.
B. Exponential (Log) Phase
1. Define the exponential phase.
2. Explain the rapid growth and cell division during this phase.
C. Stationary Phase
1. Discuss the factors leading to the stationary phase.
2. Describe the factors leading to stationary phase.
D. Death Phase
1. Explain the decline in cell numbers during the death phase.
2. Discuss the factors contributing to cell death.
IV. Measurement of Microbial Growth
A. Discuss methods for counting microbial cells (direct methods: plate counts,
direct microscopic counts, filtration; indirect methods: turbidity, metabolic
activity).
B. Explain the advantages and limitations of each method.
V. Microbial Growth in the Laboratory
A. Describe the different culture media used to cultivate
microorganisms.(Selective/differential/enriched media)
B. Know about capnophiles.
Ch7 Microbial Control
1. Define asepsis.
2. Define disinfectant/antiseptic.
3. Define aseptic conditions.
4. Define nosocomial infections.
5. Discuss the differences in antimicrobial susceptibility between bacteria,
viruses, fungi, and protozoa. Which is most resistant and least resistant?
6. Know the factors that affect the efficiency of antimicrobial methods.
I. Physical Methods of Microbial Control
A. Heat
1. Describe different heat-based control methods, such as Dry heat and moist
heat. Which is the most effective method of controlling microbes.
2. Know the advantages and disadvantages of these methods.
3. Explain the concepts of thermal death point and thermal death time and
Decimal reduction time.
4. Describe pasteurization and their uses
B. Radiation
1. Discuss the use of ionizing radiation (e.g., gamma rays) and non-ionizing
radiation (e.g., UV light) for microbial control.
2. Explain how radiation damages microbial DNA and cell structures.
A. Low Temperature
1. Explain how low temperature reduces microbial growth.
C. Filtration
1. Explain how filtration is used to remove microorganisms from liquids and gases.
Discuss the use of filtration.
IV. Chemical Methods of Microbial Control
A. Disinfectants
1. Define disinfectants and their use in controlling microbial growth
(phenol/chlorine/Alcohol/Glutaraldehye/formaldehyde/hydrogenperoxide/ethyle
ne oxide).
B. Antiseptics
1. Describe antiseptics and their applications (Iodine/alcohol/ hydrogen peroxide).
2. Know which methods are used for sterilization/sanitization
C. Sterilants
1.Discuss examples of sterilants (Glutaldehyde and ethylene oxide) used in
healthcare and laboratory settings.
Ch 8 Microbial GENETICS
1.What is Genetics?
a. Definition of genetics
 is the science of heredity; the study of genes that explain:
o how they carry information.
o How they are replicated.
o How they are passed from one organism to another.
o How they are expressed.
b. Definition of gene
 Segment of DNA or RNA in some viruses that code for functional products.
2. DNA/RNA Structure and Function
a. Understand the structure of DNA, including the double helix, nucleotides, and
base pairs.
 Structure of DNA: DNA is genetic material in all living organisms that is
made of repeating units called nucleotides.
o Each DNA Nucleotide has a compound consisting of:
 Nitrogenous base (Adenine, Cytosine, Guanine, or Thymine).
 Sugar (Deoxyribose).
 Phosphate group.
 Double helix:
o 5’ to 3 prime in one direction
o 3’ to 5’ prime in another direction
o DNA strands are held together by hydrogen bonds between
nitrogenous bases.
 Base Pairs:
 Cytosine pairs with Guanine (C = G)
 Thymine pairs with Adenine (A = T)
b. understand the differences between DNA and RNA
DNA
RNA

Double Stranded

Single Stranded

Made up of 4 nucleotides:

Made up of 4 nucleotides:
Adenine, Thymine, Cytosine, or
Adenine, Uracil, Cytosine, or
Guanine.
Guanine.

Sugar Group: Deoxyribose

Sugar Group: Ribose
B. The role of DNA in storing genetic information. Complementary base pairing
(A-T and G-C).
3. DNA Replication – Duplication of chromosome before cell division.
a. The process of DNA replication.
 DNA sequence must be replicated (duplicated) each time a cell divides, and
One “parental” double-stranded DNA molecule is converted to two identical
offsprings molecules.
b. Key enzymes involved (e.g., DNA polymerase, helicase, Ligase and their
functions).
 Helicase: Unwinds double-stranded DNA.
 DNA Polymerase: Adds complementary nucleotides continuously in leading
strand (Synthesize DNA), proofreads and repairs DNA.
 Primase: Primer is added by RNA primase (Polymerase) to show direction
what direction where to go.
 DNA Ligase: Joints discontinuous fragments of lagging strand (glues
everything). Makes covalent bonds to join DNA strands, Okazaki fragments,
and new segments in excision repair.
c. Semiconservative replication and its significance.
 Semiconservative replication: each strand acts as a template for the
production of a new strand. Each new DNA molecule has one old strand
(parent) and one new strand.
d. Know the substrate and the products?
4. Transcription
a. Definition and purpose/location of transcription.
 Transcription: is the synthesis of a complementary strand of RNA from a
DNA template.
o Purpose: A strand of mRNA is synthesized using a specific portion of
the cell’s DNA as a template.
 In other words, the genetic information stored in the sequence
of nitrogenous bases of DNA is rewritten so that the same
information appears in the base sequence of mRNA.
o Location:
 Prokaryotes – Cytoplasm
 Eukaryotes – Nucleus
b. RNA polymerase and its role.
 RNA Polymerase: binds to DNA sequence called promoter.
o A promoter starts the sequence at TAATA OR TATA BOX
 RNA Polymerase makes RNA copy of gene (transcript). Convert DNA into
RNA.
c. Steps in transcription (initiation, elongation, termination and also role of
promoter and terminator).
 Step 1: Initiation – Ribosomal subunits and mRNA assemble.
o Promoter: The starting site on a DNA strand for transcription of RNA
by RNA polymerase.
 Step 2: Start codon (AUG) binds to tRNA with methionine.
 Step 3: Elongation – Subsequent amino acids are added by translating one
codon at a time.
 Step 4: Ribosomes attach each amino acid to growing protein chains by
formation of peptide bonds.
 Step 5: Termination – When a stop codon is reached, translation stops, and
ribosome-mRNA complex falls apart.
o Terminator: The site on a DNA strand at which transcription ends.
d. Know the substrate and the products?
5. Translation
a. Definition and purpose and location of translation.
 Translation: The use of mRNA as a template in the synthesis of protein.
 Purpose: mRNA is used to make proteins.
 Location: Translation occurs on the ribosome, which is made up of two
subunits (large and small).
B. Function of tRNA
 tRNA: The type of RNA molecule that brings amino acids to the ribosomal
site where they are incorporated into proteins. tRNA molecules have an
anticodon, which recognizes codons. They carry specific amino acids to the
growing protein chain.
c. Ribosomes and their function.
 Ribosomes: The site of protein synthesis in a cell, composed of RNA and
protein.
 Function: Ribosomes attach each amino acid to growing protein chain by
formation of peptide bonds.
d. How codons and anticodons relate to translation (Function of start codon and
stop codon).
 Anticodon: The three nucleotides by which a tRNA recognizes an mRNA
codon. (Carried by tRNA).
 Codon: A sequence of three nucleotides in mRNA that specifies the
insertion of an amino acid into polypeptide. (Carried by mRNA).
o Start codon: AUG (Methionine)
o Stop Codon: UAA, UGA, UAG
 tRNA molecules have an anticodon, which recognizes codons. They carry
specific amino acids to the growing proteins chain.
6. Genetic Code
a. The genetic code and its universality.
 Genetic code is universal because all living organisms on Earth use the same
genetic code.
b. Start and stop codons.
 Start codon: AUG (Methionine)
 Stop Codon: UAA, UGA, UAG
7. Mutations
a. What are mutations?
 Mutations: are changes in the nucleotide sequence of DNA
o These changes may be harmful, beneficial, or have not effect (stay
neutral) on the individual or cell.
b. Types of mutations (point mutations, frameshift mutations, etc.).
 Silent mutations: Do not affect activity of gene product. May or may not
change amino acid sequence.
 Spontaneous Mutations: Occur spontaneously during replication.
 There are two types of mutations:
o Base Substitution: Single nucleotide is replaced with a different base.
After replication, base pair changes. It does not change the entire
frame like frameshift does, but it changes only one amino acid.
 Missense Mutation: results in amino acid substitution.
 Nonsense Mutation: Creates a stop codon which truncates
protein. Only a fragment is synthesized.
 Silent Mutation: Protein sequence and/or activity is not
altered.
o Frameshift Mutation: Several nucleotides are inserted or deleted into
a gene. These mutations may shift the reading frame of translation,
resulting in a completely different amino acid sequence after
mutation site.
c. Causes of mutations (spontaneous and induced).
 Induced
o Mutagens: are agents in the environment that cause permanent
change in DNA.
 Many chemicals, X-rays, ultraviolet light, and other forms of
radiation can cause mutations and increase mutation rate by a
factor of 10 to 1000.
 Spontaneous
o Spontaneous Mutations: Occur spontaneously during replication
9. Horizontal Gene Transfer
Mechanisms of horizontal gene transfer (transformation, transduction,
conjugation).
 Horizontal Gene Transfer: Occurs during reproduction, between
generations of cells. (Parents to Offspring).
 Horizontal Gene Transfer: Transfer of genes between cells of the same
generation. (Same generation).
 Transformation in bacteria: Genes are transferred from one bacterial cell to
another in the form of naked DNA. (naked DNA transfer between one cell to
another cell).
o Example: Transformation of bacteria in Griffith’s Experiment.
 Transformation in Bacteria: only a small percentage of donor DNA is
transferred.
 Conjugation in Bacteria: Genetic material is transferred from one bacterial
cell to another through direct contact.
o Gram negative (-ive) cells form sex pili.
o Gramp positive(+ive) cells produce sticky surfaces molecules.
o Require fairly high cell density.
 Transduction in Bacteria: Genetic material is transferred from one bacterial
cell to another through a virus (Bacteriophage)
 Bacteriophage: Virus that infect bacteria.
o Transduction may be generalized or specialized.
Ch 10 classification Microorganisms
 Taxonomy: Is the science of classifying organisms into categories or taxa, to
show degrees of similarities among organisms and it provides:
o Universal names for organisms.
o Reference for identifying organisms.
1. Phylogeny and identification
a. Systematics or Phylogeny: Is the study of the evolutionary history of
organisms, and the hierarchy of taxa reflects their evolutionary, or
phylogenetic, relationship. (Family Tree).
2. Three Domains and Characteristics
a. Bacteria Domain (Virtuosos)
b. Archaea Domain (Weirdoes)
i. Three Kingdoms:
1. Methanogens: Strict anaerobes that produce methane.
2. Extreme Halophiles: Require high salt concentration.
3. Thermoacidophiles: Live in hot, acidic environments.
c. Eukarya Domain (Predators and thieves)
3. Characteristics of animals, fungi, protozoa, plants
a. Protista (Protozoans, algae…)
i. Most are unicellular.
ii. Some are multicellular.
iii. Some are autotrophic, while others are heterotrophic.
iv. Aquatic.
b. Fungi (Mushrooms, yeasts…)
i. Multicellular, except yeast.
ii. Absorptive heterotrophs (digest food outside their body & then
absorb it).
iii. Cell walls made of Chitin.
c. Plantae (Multicellular plants…)
i. Multicellular.
ii. Autotrophic.
iii. Absorb sunlight to make glucose – Photosynthesis.
iv. Cell walls made of cellulose.
d. Animalia Multicellular animals…)
i. Multicellular
ii. Ingestive heterotrophs (Consume food & digest it inside their
bodies).
iii. Feed on plants or animals.
4. Test used for classification vs identification.
a. Classification – placing organisms in groups of relate species.
i. Putting them into groups, into a family tree.
ii. Done in research Labs.
b. Identification – Matching characteristics of an “unknown” organism
to list of known organisms.
i. Trying to identify,
ii. Done in Clinical Labs
5. Serological tests
6. DNA fingerprinting
7. PCR