Bacteriology: Is the Brach of microbiology which deals with the study of bacteria.• Prokaryotic Cells

Definition: Cells that lack a nucleus and membrane-bound organelles.

Structure

DNA floats freely in the cytoplasm (not enclosed in a nucleus).

Have a cell membrane, cytoplasm, and ribosomes.

Examples: Bacteria

Eukaryotic Cells

Definition: Cells that have a true nucleus and membrane-bound organelles.

Structure

DNA is enclosed within a nucleus.

Contains organelles like mitochondria, ER, Golgi apparatus, and lysosomes.

More complex internal organization.

Examples: Animals, plants, fungi, and protists.

Size and Complexity: Larger and more complex.

What Are Bacteria?

Definition: Bacteria are microscopic, single-celled organisms with a prokaryotic cell structure, meaning they lack a true nucleus and membrane-bound organelles.

Diversity: There are millions of different types of bacteria found all over the world—including in soil, water, air, and inside living organisms

Prokaryotic nature/no true nucleus: Bacteria lack a true nucleus and membrane-bound organelles. Their DNA floats freely in the cytoplasm.

Unicellular/single celled organisms: Each bacterium is a single celled, though some form colonies.

Cell Wall made up of peptidoglycan: Most bacteria have a rigid cell wall made of peptidoglycan, which provides shape and protection.

Posses different shapes: Common shapes include

Coccus (spherical)

Bacillus (rod-shaped)

Spirillum (spiral-shaped)

Reproduction is by asexual reproduction: They reproduce asexually through binary fission, a process where one cell splits into two identical cells

Metabolism: Bacteria can be autotrophic (making their own food) or heterotrophic (consuming organic material) and chemotrophs

Motility: Some bacteria move using flagella, while others glide or twitch.

Adaptability: Bacteria can survive extreme environments—hot springs, acidic lakes, deep-sea and vents.

Ribosomes: They contain 70S ribosomes, which are smaller than those in eukaryotic cells.

Pathogenicity: Some bacteria cause diseases in humans, animals, and plants, while others are beneficial (e.g., gut flora, nitrogen-fixing bacteria).

Structure

Function

Cell Wall

Provides shape and protection; made of peptidoglycan in most bacteria.

Cell Membrane

Controls movement of substances in and out of the cell.

Cytoplasm

Jelly-like substance where cellular processes occur.

Nucleoid

Region containing the bacterial DNA (not enclosed in a nucleus).

Nucleoid

Region containing the bacterial DNA (not enclosed in a nucleus).

Plasmid

Small circular DNA molecules; often carry antibiotic resistance genes, uv resistance, and virulence

Ribosomes (70S)

Sites of protein synthesis.

Flagella

Tail-like structures used for movement.

Pili (Fimbriae)

Hair-like structures for attachment to surfaces or other cells.

Capsule

Slimy outer layer that protects against desiccation and immune attack.

Inclusion Bodies

Storage sites for nutrients or other substances.eg gases

Endospore

Dormant, tough structure formed by some bacteria to survive harsh conditions.

Cellcomponent

Description

Functions

Cell wall

Is the outer most supportinglayer which protects theinternal structure of a cell

Protection of internal structures(supporting layer)• Gives shape to the cell• Confers stability to osmotic pressure(mucopeptide toughens the cell wall)• Role in division of bacterial• Offers resistance to harmful effect ofenvironment

Capsule

Is gelatinous secretion ofbacteria which gets organisedas a thick coat around cell wall

Protection against deleterious agents(antibacterial agents) example lyticenzymes• Contributes to the virulence of

Flagella

Are long contractilefilamentous appendages

They are organs of movements

Pilli

Are (Fimbriae) hair likefilaments that extend from thecell surface. They are shorterand straighter than flagella

They are organs of adhesion• Facilitate transfer of genetic materialsfrom one bacteria to another

Cytoplasmic/Plasmamembrane

Is a thin and elastic layersurrounding a cytoplasm. It ismade of lipoproteins andphospholipids

.Controls the movement of water, ions,nutrients and excretory substances inand out of the cell.• Secrets extracellular hydrolytic enzymes

Cytoplasm

Is a viscous watery solution orsoft gell containing a varietyof organic and inorganicsolutes

Supports cellular structures likeribosome, nutrient granules, metabolitesplasmids and nucleoid materials

Ribosomes

Are small granules and packthe whole cytoplasm.

They are the sites for protein synthesis

Nucleoid (sitefor DNA andRNA

Is the area of the cytoplasm inwhich DNA and RNA arelocated

To store genetic information• Responsible for mutation of a bacteria

Eukaryotic Cells

Definition: Cells that have a true nucleus and membrane-bound organelles.

Structure

DNA is enclosed within a nucleus.

Contains organelles like mitochondria, ER, Golgi apparatus, and lysosomes.

More complex internal organization.

Examples: Animals, plants, fungi, and protists.

Size and Complexity: Larger and more complex

Nucleus: Contains the cell’s DNA enclosed within a nuclear membrane, allowing for organized gene expression and regulation.

Membrane-Bound Organelles: Includes mitochondria (energy production), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (packaging and transport), lysosomes (digestion), and chloroplasts (photosynthesis in plants).

Cytoskeleton: A network of protein filaments (microtubules, microfilaments, intermediate filaments) that maintains cell shape, enables movement, and organizes organelles

Multicellularity: Found in multicellular organisms with specialized cell types.

Plasma membrane: Phospholipid bilayer that regulates entry and exit of substances.

Compartmentalization: Organelles allow distinct environments for specialized biochemical processes.

Intracellular transport: Vesicles shuttle materials between organelles and to the membrane.

Larger size: Typically 10–100 µm, much larger than prokaryotic cells

Features

Prokaryotes

Eukaryotes

Nucleus

No enclosing membrane

Enclosed by a membrane

Nucleolus

Absent

Present

Cell wall composition

Usually containpeptidoglycan

Usually contain cellulose orchitin

Mitochondria

Absent

May be present

Location ofchromosome

In the cytoplasm, usuallyattached to the cell membrane

Within a true nucleus separatedfrom the cytoplasm by anuclear membrane

Reproduction

Normally asexual

Asexual or sexual

Motility structures

Present

Absent

Cell Membrane: Both types of cells are enclosed by a lipid bilayer that regulates the movement of substances in and out of the cell

Cytoplasm: Each cell contains cytoplasm, a gel-like substance where cellular processes occur.

DNA as Genetic Material: Both use DNA to store genetic information, although it’s organized differently (nucleus vs. nucleoid)

Ribosomes for Protein Synthesis: Both have ribosomes, which are essential for translating genetic instructions into proteins

Basic Metabolic Functions: They carry out essential life processes like energy production, waste elimination, and reproduction.

Cell Division: Both reproduce by cell division—prokaryotes typically by binary fission, and eukaryotes by mitosis or meiosis

Bacteria are classified depending on different factors, bellow are the factors which can be considered when classifying bacteria

1.Shape(morphology) – coccus, bacillus, spirillum, Vibrio

Classification of Bacteria according to Staining Characteristics.

They have cell wall made up of peptidoglycan.

The composition and amount of peptidoglycan is the basis for Gram stain classification

3.Ability to grow in presence or absence of air

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Ability to form spores

5.Biochemical reactions

6.Type of flagella

7.pathogenic featues

Nutrition requirement

Classification of Bacteria According to Morphology/Shape

Cocci

These are round or oval shaped bacteria.

When multiplying cocci may form

Pairs (called diplococci for example meningococci and gonococci)

Chains (called streptococci example Streptococcus pyogenes)

Irregular groups or clusters (called staphylococci, example is staphylococcus aureus)

Classification of Bacteria According to Morphology/Shape cont…

Bacilli

These are rod shaped bacteria.

When multiplying bacterial rods do not usually remain attached to one another, but separate.

Occasionally however, they may form

Chains, example are Streptobacilli

Branching chains, example are Lactobacilli

Mass together; example is Mycobacterium leprae

Remains attached at various angles example Corynebacterium diphtheria

Classification of Bacteria According to Morphology/Shape cont…

These are small regularly coiled, rigid organisms.

Examples Spirillum minus

Comma shaped

These are small slightly curved rods (comma shaped). Example Vibrio cholera

Spirochaetes and Spiral

These are flexible, coiled, motile organisms they progress by rapid body movement.

Example, treponema species, borrelia species, and leptospires and spirillum minus

Bacteria

Classification of Bacteria basing on gram staining

Gram positive bacteria

When stained by Gram stain, appears blue reflecting the colour of primary stain (either gentian violet, crystal violet or methyl violet). Examples, Staphylococci species, Streptoccoci species. Clostridium tetani.

Gram negative bacteria

are bacteria which appears red, after losing the colour of primary stain and adapting the colour of a counter stain (dilute carbofuchsin or safranin, or neutral red) when stained by gram stain o Examples, neisseria species, salmonella species, haemophilus species

Classification of Bacteria basing on spore forming

Spores are highly resistant dormant state of bacteria with dense thick walls able to withstand dehydration heat, cold and action of disinfectants.

In this kind of classification there are

Spore forming bacteria for examples bacillus species and clostridium species

Non spore forming bacteria for examples corynebacteria species like corynebactrium diphtheria

Classification of Bacteria basing on oxygen (air) requirement

some bacteria grow and repduce in the presence of oxygen (aerobic bacteria)

Example bacillus anthracis

And others grow and reproduce in absence of oxygen (anaerobic bacteria)

for example clostridium species.

1.Catalase test

Presence of catalase enzyme which breaks down hydrogen peroxide into water & oxygen.

Catalase positive bacteria produce produce bubbles (O2) eg staphylococcus

2.Coagulase test

A coagulase test is a biochemical test that is used to differentiate Staphylococcus aureus from other Staphylococci species like S. epidermidis and S. saprophyticus on the basis of the ability to produce the coagulase enzyme.

There is production of coagulase enzyme which causes blood clot(converts fibrinogen into fibrin)

Flagella are long thin projections that extend from the cell, arising from one or more locations on the surface of the cell wall and cell membrane, some bacteria posses these motility structures while others do not.

The flagella can be classified as follows

Atrichious –absence of flagella e.g. Lactobacilli

Monotrichious -presence of a single flagella at one end. e.g.Vibrio cholera

Amphitrichious – presence of a single flagella at both ends. e.g. Spirillum

Peritrichious – presence of flagella all over the cell surface. e.g.E.coli,Salmonella.

Lophotrichous –bacteria with tuft or cluster of flagella arising from one side

Example Helicobacter pylori, Pseudomonas spp

Autotrophs

Use carbon dioxide (CO₂) as their carbon source to obtain energy

Can synthesize organic compounds from inorganic substances.

Examples: Nitrosomonas, Nitrobacter

Heterotrophs

Require organic compounds as their carbon source.

Depend on other organisms for nutrition.

Examples: Escherichia coli, Bacillus subtili

Phototrophs

Derive energy from sunlight.

Include photoautotrophs (e.g., cyanobacteria) and photoheterotrophs (e.g., Rhodobacte

Pathogenic Bacteria: Cause disease in humans, animals, or plants. Examples: Mycobacterium tuberculosis, Streptococcus pyogenes.

Opportunistic Pathogens: Normally harmless but can cause disease in immunocompromised hosts. Example: Pseudomonas aeruginosa.

Non-Pathogenic Bacteria: Do not cause disease and may be beneficial. Example: Lactobacillus species.

What are the structural features of bacterial cell? • What are the differences between prokaryotic cell and eukaryotic cell?• What are the 5 criteria for classification of bacteria and give examples?