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Bacteria – Morphology & Classification

Dr Nehal Draz. Bacteria – Morphology & Classification. Introduction:. Microorganisms – several classes of living beings Based on the organization of their cellular structures, all living cells can be divided into two groups: eukaryotic and prokaryotic

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Bacteria – Morphology & Classification

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  1. Dr NehalDraz Bacteria – Morphology & Classification

  2. Introduction: • Microorganisms – several classes of living beings • Based on the organization of their cellular structures, all living cells can be divided into two groups: eukaryotic and prokaryotic • Eukaryoticcell types- Animals, plants, fungi, protozoans, and algae • Prokaryotic cell types - bacteria & blue green algae

  3. Bacteria are protista • Kingdom protista is the 3rd major branch of micro-organisms that includes: • Higher protista (eukaryotic) 1- protozoa 2- fungi 3- Algae except blue green algae • Lower protista (prokaryotic) 1- bacteria 2- blue green algae

  4. CLASSIFICATION I- based on morphology (old) • 1- Higher bacteria Actinomyces (filamentous branching Leptospira (filamentous non branching) • 2- Lower bacteria - Simple unicellular - Classified acc to morphology into: Cocci Bacilli curved spiral filaments

  5. Lower Bacteria curved bacilli cocci Higher Bacteria Spiral Actinomyces

  6. Arrangement of bacteria: Cocci Coccus Tetrad – groups of four Cocci in pair – Diplococcus Cocci in chain - Streptococci Cocci in cluster - Staphylococci Sarcina – groups of eight

  7. Arrangement of bacteria: Bacilli Dr Ekta Chourasia

  8. CLASSIFICATION II- based on molecular biol &molecular genetics (new) 1- Nucleotide Base Composition: - The mol. % of guanine + cytosine (G + C) in the total DNA is most often used • For any species the G + C content is relatively fixed 2- Nucleotide Base Homology: • Can be classified into groups • On thebasis of their DNA base sequence 3- Nucleotide Base Sequence: - Depends on base sequence homology in ribosomal RNA

  9. Bacterial Cell Structure Essential components: basic structure present in all bacteria, e.g. cell wall, Cytoplasmic membrane, cytoplasm, nuclear material. • Non essential components: present in some bacteria species, e.g. capsule, fimbria, flagella, spores

  10. Cell Wall • The cell wall is the outermost component of bacterial cell. • Functions: 1- maintain shape 2- support cytoplasmic membrane 3- Role in cell division 4- protection against antibiotics & antibodies 5- Antigenicity 6- Staining reaction to Gram

  11. Composition of cell wallI- Gram positive celll wall Two layers 1- Peptidoglycan: constitute 80% of cell wall thickness. 2- Teichoic acid It is located in the outer layer of the Gram positive cell wall. It is antigenic.

  12. 2- Gram negative cell wall • Peptidoglycan:constitutesup to5-10% of Gram negative cell wall. • Outer membrane: formed of bilayered phospholipids It has special channels, consisting of proteins called porins which allow passive diffusion of low molecular weight compounds like sugar, and amino acids. • Periplasmic space: a space between the inner cytoplasmic membrane and outer membrane where the single sheet of peptidoglycan layer is present. contains gel-like solution of protein.

  13. Unusual lipoproteins layer: It stabilizes the outer membrane layer with tetrapeptide side chain of peptidoglycan. • Lipopolysaccharides (LPS) layer: attached to outer membrane. (endotoxin of Gram- negative bacteria). (somatic O antigen). This layer is barrier to hydrophobic molecules.

  14. G+ve G-ve

  15. Property of bacteria Gram Positive Gram Negative Thickness of wall 20-80 nm 10 nm Number of layers in wall 1 2 Peptidoglycan content >50% 10-20% Teichoic acid in wall + - Lipid & lipoprotein content 0-3% 58% Protein content 0% 9% Lipopolysaccharide 0 13% Sensitive to penicillin Yes Less sensitive Digested by lysozyme Yes Weakly Summary of the differences between Gram positive & Gram negative bacteria

  16. Cytoplasmic Membrane • It lies just inside the peptidoglycan layer. It is a phospholipids bilayer that contains protein. It is similar to eukaryotic cell membrane but does not contain sterol except in mycoplasma. • Mesosomesare invagination of the cytoplasmic membrane inside the cytoplasm. Two types of mesosomes are known as lateral and septal. Septalmesosomes are involved in cell division where bacterial DNA is attached.

  17. Function of Cell Membrane: • Selective permeability: Molecules move across the membrane by simple diffusion or active transport. • Excretion of extracellular enzymes and toxins. • Respiration: the cytochrome and respiratory enzymes are localized in the cytoplasmic membrane. • Play an important role in cell division.

  18. Cytoplasm • The cytoplasm of the bacterial cell is a viscous watery solution or soft gel that contains a variety of organic and inorganic solutes. A- Mesosomes: • These are invagination of cytoplasmic membrane. • It is the site of attachment of DNA chromosome during cell division. • Site of respiratory activity of the cell. • Increase surface area of the membrane, thus increase efficiency of active transport.

  19. B- Ribosomes: • They are complex structure composed of 60% RNA and 40% protein. They are the site of protein synthesis in the cell. • They have sedimentation constant of 70S being composed of 30S and 50S subunits.

  20. C- Inclusion granules: • Round granules observed in cytoplasm of many bacteria. • These are not permanent or essential structures. • They appear to be either stored energy or nutrient reserve concerned with cell metabolism, e.g. volutin granules (Metachromatic granules of Corynebacterium diphtheria)

  21. D- Plasmids: • Extra chromosomal double stranded circular DNA that carry certain genetic information, e.g. antibiotic resistant toxin production, virulence, … etc. • Dispensable: not necessary for life of the cell. • Autonomous: multiply independent of the host. • Transmissible: can transfer to other bacteria by conjugation, transformation, or transduction.

  22. E- The Nuclear Body: • The genetic information of the bacterial cell is contained in single circular DS-DNA molecules, which constitutes the bacterial chromosome. • The nuclear body does not have nuclear membrane, mitotic apparatus, or histones.

  23. Structures outside the Cell Wall Capsule • It is present only in some bacteria outside the cell wall. It is gelatinous in nature. The capsule may be polysaccharide, polypeptide or hyalouronic acid • Capsules usually formed in vivo only and not stained by ordinary stain. The capsule is antigenic. • The capsule has antiphagocytic function so it determine the virulence of many bacteria. It also plays a role in attachment of the organism to mucous membrane

  24. Stained by negative staining using India Ink • Can be demonstrated by Quellung reaction (capsule swelling reaction)

  25. Flagella • Flagellae are the organs of motility. They are thread like appendages, protein in nature, formed of flagellin protein which is antigenic (H Ag). • They can not be stained by gram stain. They have special stain. • According to their number, they may be monotrichate, amphitrichate, lophotrichate, peritrichate.

  26. monotrichious lophotrichious peritrichious

  27. Fimbriae (pili) • They are a hair like filaments, formed of protein called pillin which is antigenic in nature. Fimbriae are responsible for the attachment of bacteria to specific receptors of human cell (Adherence). • There are special types of pili called sex piliinvolved in the process of conjugation(transfer of DNA between bacteria). • Fimbriae are shorter and thinner than flagella.

  28. Bacterial Spores (Endospores) • Some bacterial genera are capable of forming highly resistant resting phase or endospores, e.g. Bacillus group and Clostridium group. • Endospores do not reproduce and exhibit absolute dormancy. Spore formation occurs in response to unfavourable conditions, e.g. depletion of nutrition, accumulation of metabolites or unsuitable temperature or moisture. • When the unsuitable conditions changed, the spore germinates to the vegetative form which can multiply.

  29. Shape & position of bacterial spore Oval central Non bulging Spherical central Oval sub terminal Oval sub terminal Bulging Oval terminal Spherical terminal Free spore Dr Ekta Chourasia

  30. Bacterial Taxonomy: Nomenclature • Two kinds of name are given to bacteria • Casual / common name – for local use, varies from country to country e.g. “typhoid bacillus” • Scientific / International Name – same all over world, consists of two words (in Italics) e.g. Salmonella typhi, Staphylococcus aureus

  31. A smile from you can bring happiness to anyone, even if they do not like you. Nehal Draz

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