University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
the structure of bacterial cell
Q1: structure of bacterial
Despite their lack of complexity compared to eukaryotes, a number of bacterial
structures may be defined:
● Essential structures :
1. Cell wall .
2.Cell membrane.
3.Cytoplasm .
4. Nuclear material .
● Special structures :
1. Capsule .
2. Flagella .
3. Pili .
4. Endospores (spores) .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
Only plasma membrane, which belonging to cell envelope, is the essential component for any
bacteria
Bacterial structure is considered at three levels.
1. Cell envelope proper: Cell wall and cell
membrane.
2. Cellular element enclosed within the cell
envelope : ribosomes, nuclear apparatus, and
cytoplasmic granules.
3. Cellular element external to the cell envelope:
Flagellum, Pilus and Glycocalyx.
1. Cell envelope proper :
● Essential structures
1. Cell Wall : It is arigid ,seim-elastic protective covering present outside
the cell . Multi layered structure and constitutes about 20% of the
bacterial dry weight. the chemical composition of cell wall is rather
complex and is made up of Peptidoglycan or mucopeptide ( N-acetyl
glucosamine, N-acetyl muramic acid and peptide chain of 4 or 5
aminoacids).
● based on Gram staining characteristics that reflect major structural
differences between the two bacterial groups:
1. gram-positive cell wall with a thick peptidoglycan layer .
2. gram-negative cell wall with a thin peptidoglycan layer and an
overlying outer membrane .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
◄ Gram staining : is a common technique used to differentiate two
large groups of bacteria based on their different cell wall
constituents. The Gram stain procedure distinguishes between Gram
positive and Gram negative groups by coloring these cells pink or
purple.
1. Gram positive bacteria:
These bacteria give a positive result to the gram staining
test indicating the presence of a thick cell wall.
Example: Staphylococcus aureus
2. Gram negative bacteria:
These bacteria do not give a result for gram staining
because of their thin peptidoglycan layer.
Example: Escherichia coli
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
● Components of cell wall of Gram negative bacteria:
1. Peptidoglycan .
2. Lipoprotein .
3. Phospholipid .
4. Lipopolysaccharide .
● Components of cell wall of Gram positive bacteria :
1. Peptidoglycan .
2. Teichoic acid .
◄ the role of cell wall in bacteria provide protection and gives shape to the
cell .
2. Cell membrane: it is the out most elastic covering of the cell made up
of lipids and proteins. the main job of the cell membrane is :
a. control permeability .
b. transport e’s and protons for cellular metabolism.
c. contain enzymes to synthesis and transport .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
cell wall substance and for metabolism .
d. secret hydrolytic enzymes .
e. regulate cell division .
2. Cellular element enclosed within the cell envelope :
3. Cytoplasm :It is a jelly like, semi- fluid substance . made up of 80% water,
nucleic acids, proteins, carbohydrates, lipid and inorganic ions etc. It contains
ribosomes , nuclear material and other cell inclusions.
4. Nuclear material : It is long filament of DNA tightly coiled inside the
cytoplasm .
3. Cellular element external to the cell envelope:
● Special structures :
1. Capsule :It is a gelatinous outer layer secreted Some bacteria are
surrounded by a gelatinous substance which is composed of
polysaccharides or polypeptide or both . A thick layer of glycocalyx
bound tightly to the cell wall .
◄ Capsules are mainly present in pathogenic bacteria .the main function of
capsule is to protects cell from desiccation and antibiotics. The sticky
nature helps them to attach to substrates like plant root surfaces, Human
teeth and tissues. It helps to retain the nutrients in bacterial cell .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
2. Flagella: Flagella are responsible for the motility of the bacteria. They
are thin structures of around 20μm, but long (3 to 12 μm), wavy
filamentous appendages. A bacterium can have one flagellum or a cluster of
flagella . also It is composed of protein named as flagellin. The
flagellar antigen in motile bacterium is named as H
(Hauch) antigen, flagella are used for locomotion.
● Based on the number and position of flagella there are different types of
bacteria :
1. Monotrichous: Bacteria with single polar flagellum .
2. Lophotrichous: Bacteria with bunch of flagella at one .
3. Amphitrichous: Bacteria with flagella at both poles .
4. Peritrichous: Bacteria with flagella all over their surface.
5. Atrichous: Bacteria with no flagellum .
Flagellation in bacteria
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
3. Pili: It is hair like structure composed of protein (pilin).
they have Two types (Based on function):
1. Common pili: The structure for adherence to cell surface .
2. Sex pili: The structure for transfer of genetic material from the donor to the
recipient during the process of conjugation.
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
4.Endospores (spores): Resting cells which are capable of surviving under
adverse environmental conditions like heat, drying, freezing, action of toxic
chemicals and radiation .
.• Bacterial spore is smooth walled and oval or spherical in shape .
• It does not take up ordinary stains .
• It looks like areas of high refractivity under light microscope .
• It is significant in spread of disease and indicator of sterility of
materials .
◄ Bacteria are very small unicellular microorganisms ubiquitous in nature.
They are micrometers (1µm = 10-6 m) in size. They have cell walls
composed of peptidoglycan and reproduce by binary fission. Bacteria vary
in their morphological features.
Based on Structure or shapes of bacteria they have :
Coccus (pleural: Cocci):
Spherical bacteria; may occur in pairs (diplococci), in groups of four (tetracocci), in grapelike clusters (Staphylococci), in chain (Streptococci) or in cubical arrangements of eight
or more (sarcinae).
For example: Staphylococcus aureus, Streptococcus pyogenes
Bacillus (pleural: Bacilli):
Rod-shaped bacteria; generally occur singly, but may occasionally be found in pairs
(diplo-bacilli) or chains (streptobacilli).
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
For example: Bacillus cereus, Clostridium tetani
Spirillum (pleural: Spirilla):
Spiral-shaped bacteria
For example: Spirillum, Vibrio, Spirochete species.
Some bacteria have other shapes such as:
Coccobacilli: Elongated spherical or ovoid form.
Filamentous: Bacilli that occur in long chains or threads.
Fusiform: Bacilli with tapered ends.
Q2: Sterilization: Destruction of all forms of microbial
life including spores.
● Sterilization and disinfecting agents are divides into two
groups these are:
1. Chemical means’s of sterilization and disinfection .
2. Physical means’s of sterilization .
1. Chemical means’s of sterilization & disinfection
• These chemical agents destroy any type of microbes without showing any form
of selectivity .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
.
Classification of chemical mean’s of sterilization and disinfection
◄ Chemical agents that damage the cell membrane.
• Surface Active Agents
• Phenols
• Organic solvents (Alcohol).
• Chemical agents that denature proteins.
• Acids and alkalizes Acids like acetic acid.
Anti-septic agents
• Disinfectants that are applied on an animate bodies.
• Never be toxic to cells,
• Should never change nature of skin
• E.g. 70% alcohol, and I
● Examples:The commonly used gases for sterilization are a combination of
ethylene oxide and carbon-dioxide. Here Carbon dioxide is added to minimize
the chances of an explosion. Ozone gas is another option which oxidize most
organic matter. Hydrogen peroxide, Nitrogen dioxide, Glutaraldehyde and
formaldehyde solutions, Phthalaldehyde, and Peracetic acid are other
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
examples of chemicals used for sterilization. Ethanol and IPA are good at
killing microbial cells, but they have no effect on spores.
1. Physical methods :
◄ Heat It is the most reliable and universally applicable method
• Can be divided into dry heat and Moist heat
1. Dry heat It is less efficient and requires high temperature and long period
heating than moist heat.
a. Red heat: Inoculating wires, loops and points of forceps are
sterilized by holding them in the flame of a Bunsen burner until
they are red hot.
2. Moist heat : It is preferred to dry heat due to more rapid killing
• Moist heat can be used by the following methods.
a. Boiling: It is not reliable method of sterilization. It is done by applying
100∘c for 30 minutes.
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
• Used for sterilizing catheters, dressing
b. Pasteurization: It is the process of application of heat at temperature of 62∘c
for 30 minutes or 72∘c for 15 seconds followed by rapid cooling to discourage
bacterial growth.
◄ The aim is to kill pathogenic bacteria to make food safe to eat.
●
Example: In most labs, this is a widely used method which is done in
autoclaves .
Q3: culture media: A growth medium or culture medium is a solid,
liquid or semi-solid designed to support the growth of microorganisms .
● Types of culture media
The main types of culture media are:
1. Basic media : These are simple media that will support the growth
of micro organisms that do not have special nutritional requirements .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
● Example : Nutrient Agar and Nutrient broth .
2. Enriched or enrichment media : Enriched These media are required for
growth of organism with extra nutritional requirements such as H. influenza
Neisseria spp, and some streptococcus species.
● Example: - Blood Agar (contain whole blood) and Chocolate agar
(contain lyzed blood) .
● Enrichment media : Fluid medium that increases the number of a
pathogen by containing enrichments and/ or substances that discourage
multiplication of unwanted bacteria.
● Example: Selenite Faecal (F) broth is used as an enrichment medium for
Salmonellae in faeces or urine prior to subculture.
3. Selective media : These are media which contain substances that prevent or
slow down growth of micro- organisms other than pathogen for which the
media are intended.
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
◄ The medium is made selective by incorporation of certain substances like
bile salt, crystal violet, antibiotics, etc.
● Example:.
1. Thiosulphate citrate bile salt sucrose agar(TCBS) - is alkaline
medium and selective for V. cholera.
2. Xylose Lysine Deoxy Cholate (XLD) agar - selective for
Salmonella and Shigella .
4. Indicator (differential) media :These are media to which dyes or
other substances are added to differentiate micro-organisms .
● Many differential media distinguish between bacteria by incorporating
an indicator which changes colour when acid is produced following
fermentation of a specific carbohydrate .
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
● Example : Mac Ckonkey agar - contain neutral red as an indicator and
lactose as carbohydrate.
5. Transport media : These are mostly semisolid media that contain
ingredients to prevent the overgrowth of commensals and ensure the
survival of aerobic and anaerobic pathogens when specimens cannot be
cultured immediately after collection.
◄ Their use is particularly important when transporting
microbiological specimens form health centres to the district
microbiological laboratory or regional public .
● Example :
1. Cary-Blair medium :– is used for preserving and transporting enteric
pathogens.
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
2. Amies transport medium:- is used for transportation of gonococci.
Q4 Inflammation related enzymes
1. Hyaluronidase :(spreading factor): degrades hyaluronic acid, which is the ground
substance of subcutaneous tissue.
2. Streptokinase :( fibrinolysin) activates plasminogen to form plasmin, which
dissolves fibrin in clots, thrombi, and emboli.
Toxins and hemolysins
1. Erythrogenic toxin: causes the rash of scarlet fever.
2. Streptolysin O: is a hemolysin that is inactivated by oxidation (oxygen-labile). It
causes beta-hemolysis only when colonies grow under the surface of a blood agar
plate .
3. Exotoxin B: is a protease that rapidly destroys tissue and cause necrosis .
◄ S. pyogenes (group A streptococcus) is the leading bacterial cause of
pharyngitis and cellulitis. It is an important cause of impetigo,
necrotizing fasciitis, and streptococcal toxic shock syndrome. It is also
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
the inciting factor of two important immunologic diseases, namely,
rheumatic fever and acute glomerulonephritis.
Q5: Classification of streptococci
1. Beta-hemolytic streptococci: They are subdivided in to :
• Group A includes S. pyogens
• Group B includes S. agalacteia
• Group D includes S. bovis
2. Alpha-hemolytic streptococci: includes S. pneumonia.
3. Non-hemolytic (viridans) streptococci: e.g., S.
mitis, S. sanguis, and S. mutans .
Laboratory Diagnosis:
Gram-stained smears are useless in streptococcal pharyngitis because
viridans streptococci are members of the normal flora and cannot be
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
visually distinguished from the pathogenic S. pyogenes. However, stained
smears from skin lesions or wounds that reveal streptococci are
diagnostic Cultures of swabs from the pharynx or lesion on blood agar
plates show small, translucent beta-hemolytic colonies in 18–48 hours.
Name: Huda Mahmoud Barre
class: 2A / ML
ID: 1819133
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University Of Hargeisa
Course Of Bacteriology
Date : 15\04/2020
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University Of Hargeisa
Course Of Bacteriology
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University Of Hargeisa
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