its brief introduction of microbiology and microorganisms such as bacteria, viruses, fungi, and parasites

1. General Microbiology & Immunology
MAC211-MAC322

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Definition of Microbiology
• It is the science concerning studying of microorganisms too
small to seen by the naked eye.
• This microorganisms which include groups of organisms:
bacteria, fungi, protozoa, and viruses.

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Animal Kingdom: Multi-cellular motile organisms, which feed
heterotrophically
Plant Kingdom: Multi-cellular organisms, which feed by photosynthesis
 Protista Kingdom: Protozoa and single-celled algae
Fungus Kingdom: Fungi
Monera Kingdom: ( Bacteria and blue green algae)
Parallel to these Kingdoms, the Viruses, which should be called Kingdom
Virus for they are becoming very important factors that they could affect the
evolution of Animal and Plant Kingdoms.
Classification of Organisms

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Prokaryotes (from the Greek words meaning prenucleus) and Eukaryotes
(have true nucleus) are chemically similar, in the sense that they both contain
nucleic acids, proteins, lipids, and carbohydrates.
 They use the same kinds of chemical reactions to metabolize food, build
proteins, and store energy.
 The structure of cell walls and membranes, and the absence of organelles
(specially cellular structures that have specific functions) distinguish
prokaryotes from eukaryotes.
Prokaryotes and Eukaryotes

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1. Prokaryotes not having a true nucleus, i.e. DNA is not enclosed within a
membrane.
2. They did not contain organelles such as mitochondria and lysosomes.
3. Most prokaryotes have a rigid cell wall that contain peptidoglycan (polymer
of amino acids and sugars).
4. They usually divide by binary fission. During this process, the DNA is
copied, and the cell splits into two daughter cells.
The chief distinguishing characteristics of Prokaryotes are
as follows:

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1. Their DNA is found in the cell’s nucleus, which is separated from the
cytoplasm by a nuclear membrane, and the DNA is found in multiple
chromosomes.
2. Their DNA is consistently associated with chromosomal proteins
3. They have a number of organelles, including mitochondria, endoplasmic
reticulum, Golgi apparatus , lysosomes, and sometimes chloroplasts.
4. Their cell walls, when present, are chemically simple.
5. Cell division usually involves mitosis.
Eukaryotic have the following distinguishing
characteristics:

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 By the end of this part you should understand what is :
1. Bacteria;
 Bacterial shapes.
 Bacterial cell wall, and some bacterial cell structures (Capsule, Appendages, Spores).
2. Diagnostic of Microbiology;
 Direct detection or visualization of microorganism (G stain, Acid fast Stain).
3. Bacterial Growth.
Lecture 2 : Bacterial Structure and Function

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Taxonomy
is the science of classification, identification and nomenclature.
 Classification
is the arrangement of organisms into groups (taxa) on the basis of their
similarities and differences. In contrast,
Identification
is the process of determining that a new isolate belongs to a particular taxon; the
aim of classification is to define these taxa at the genus or species level. e.g.
Streptococcus mutans; the genus is ‘Streptococcus’ and the species is ‘mutans
Genus. Species.
A bacterium given a name consisted of genus-species (italicized or underlined), e.g.,
Staphylococcus aureus .

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Bacterial species are identified based on a multitude of
criteria

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II- Bacterial Cell Morphology and Staining characteristics

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Gram +ve and Gram -ve cocci

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Diplococci eg Neisseria gonorrhoeae

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Streptococci eg Streptococcus pyogenes

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Staphylococci eg Staphylococcus aureus

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Bacilli or rod shape
GRAM +VE AND GRAM -VE ROD
Bacillus subtilis Escherichia coli

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Spirals spirochetes & spirillum
V. cholerae

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Cell Wall: A rigid structure outside of cytoplasmic
membrane. The major component of the cell wall is
peptidoglycan.

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Cell wall: of typical bacterial cell
 A rigid structure outside of cytoplasmic membrane.
 The major component of the cell wall is peptidoglycan.
 The main functions of the bacterial cell wall is to
maintain the shape of the organisms and prevent cell
lysis.

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Did you think the bacterial cell can live without cell wall?
Bacteria cannot live without cell wall.
Bacterial cell cytoplasm contains high solute concentration and exert
a great pressure on the membrane
(2 atmospheres in E. coli, about the same as the pressure in an
automobile tire). Bacteria typically reside in an environment with a low
solute concentrate. Without a wall the cell would swell and burst.

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Bacterial cell wall structure
The space between the cell wall and the plasma membrane is called the periplasm.
Periplasm controls molecular traffic entering and leaving the cell.

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Peptidoglycan of bacteria
 Cell wall peptidoglycan is unique to bacteria and may be the target of host
defense or antibiotics Lysozyme (found in tear and saliva) breaks the β 1-4
linkage of glycosidic bonds between N-acetylmuramic acid and N-acetyl
glucosamine.
 Digestion of the cell wall peptidoglycan leads to cell lysis due to the high
solute content of the cytoplasm.
 Antimicrobial agents that interfere with the cell wall synthesis include ß-
lactam antibiotics (e.g., penicillin, cephalosporins), cycloserine, vancomycin, and
bacitracin.

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Why bacteria require a cell wall?
Bacteria require a cell wall to:
1. Give the specific shape
2. protect them from the effects of changes in pressure.
3. Prokaryotic walls contain unique chemical compounds not found
in eukaryotes.
4. Cells that stain Gram negative have a thin layer of
peptidoglycan, and an outer membrane as part of the cell wall.

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Gram+ve bacteria have multiple thick (up to 20 or more)
peptidoglycan layers with extensive cross-linking between glycan
chains. Simple cell wall Gram+ve bacteria also possess teichoid acid
and lipoteichoid acid not found in Gram-ve organisms.
In Gram-ve bacteria, the peptidoglycan layers are relatively thin
(usually 1-2 layers) and complex. They do not have teichoid or
lipoteichoid acids. Gram-ve bacteria possess outer membrane (LPS)
which is not found in Gram+ve bacteria.

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This outer membrane is similar to the plasma membrane, but is
less permeable and composed of lipo-polysaccharides (LPS).
LPS is a toxin substance classified as an endotoxin, which is
unique to Gram-ve bacteria.

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 The outer membrane of gram negative also contains relatively high
content of proteins. One of the major proteins in outer membrane is the
porin.
 Most porins are proteins containing three identical subunits to form pores
that traverse (cross) the outer membrane. The pores allow passage of
small hydrophilic molecules. Thus, outer membrane is relatively
permeable.

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The outer membrane is not permeable to larger
molecules such as enzymes.
The space between cytoplasmic membrane and outer
membrane is the periplasmic space. The space contains
hydrolytic enzymes, binding proteins of transport systems
(for active transport of certain molecules into cytoplasm),
and binding proteins for chemotaxis system.

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LPS: consists of lipid A, core polysaccharide, and O-specific
polysaccharide.
LPS has very powerful biological activities. The activities are
associated with the lipid A portion of the LPS.
The LPS may activate complement system, activate B cells, activate
macrophage, induce secretion of interleukin 1 an 6, tumor necrosis
factor, cause endotoxin shock, and induce fever.

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Bacterial cell wall structure

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Atypical bacterial cell
Mycobacteria have a peptidoglycan layer (slightly different structure),
surrounded by a wax-like lipid coat of mycolic acid (large α-branched β-hydroxy
fatty acids. These bacteria are described as acid-fast staining. The coat is
responsible for virulence and is antiphagocytic.
BACTERIAL EXCEPTIONS

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Other Surface Structures
1- Capsules (also called slime), polysaccharide, not essential for the
viability the bacteria, may promote adherence of the bacteria to host, or
act as a barrier to substances harmful to the bacteria.
B. anthracis produces a polypeptide capsule.

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The importance of capsule:
1. One of the virulence (severity) agent and (antibiotic
resistance).
2. Identification by using the antiserum against the capsule
polysaccharide.
3. Capsule polysaccharide can be used as the antigen in some
vaccine, these poly saccharides are capable to eliciting the
protective antibodies.
4. The capsule may play a role in
the infection via the adherence process which
is the very early infection step.

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2-
flagellaare simple structures that act as propellers by rotating.

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Examples of bacterial flagella arrangement schemes: (A) monotrichous; (B) lophotrichous;
(C) amphitrichous; (D) peritrichous.

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3- Fimbriae and Sex Pili
Fimbriae or pili or common pili, hair-like structure on the surface of the
bacteria, promote adhesion (attachment )of bacteria.
Sex pili: essential for transferring DNA from the donor bacterium to the recipient
bacterium in a process called “conjugation”

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4. Spores: Some bacteria, such as members of the genera Bacillus (e.g.,
Bacillus anthracis) and Clostridium (e.g., Clostridium tetanii or botulinum) (soil
bacteria), are spore formers.
Under harsh environmental conditions, such as the loss of a nutritional
requirement, these bacteria can convert from a vegetative state to a dormant
state, or spore.
The location of the spore within a cell is a characteristic of the bacteria and
can assist in identification of the bacterium.

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Spores position
1. Central
2. Terminal
3. Sub-treminal

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1- DNA must duplicate
2- Duplicated DNA isolated and surrounded by its own cytoplasm and
membrane
3- A coat begins to develop around the duplicated
DNA
5- Spore is released
4- formation of Spore

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The spore is a dehydrated, multishelled structure that protects the bacteria. It
contains a complete copy of the chromosome, and a high concentration of calcium
bound to dipicolinic acid. The spore has an inner membrane, two peptidoglycan
layers, and an outer keratin-like protein coat. The structure of the spore protects
the genomic DNA from intense heat, radiation, and attack by most enzymes and
chemical agents. In fact, bacterial spores are so resistant to environmental factors
that they can exist for centuries as viable spores. Spores are also difficult to
decontaminate with standard disinfectants.
4. Spores:

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The germination of spores into the vegetative state is stimulated by
disruption of the outer coat by mechanical stress, pH, heat, or another
stressor and requires water and nutrient. The process takes approximately 90
minutes. After the germination process begins, the spore will take up water,
swell, shed its coats, and produce one new vegetative cell identical to the
original vegetative cell, thus completing the entire cycle. Once germination has
begun and the spore coat has been compromised, the spore is weakened,
vulnerable, and can be inactivated like other bacteria.
4. Spores:

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The binary fission
Remember that spores are not a reproduction methods

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Thank You