Bacterial morphology & anatomy


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Detailed anatomy of typical Bacterial cell with description about all organelles

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Bacterial morphology & anatomy

  1. 1. Bacterial Morphology & Anatomy - Kalpesh Zunjarrao
  2. 2. Introduction: • Several classes of living organisms • Based on the organization of their cellular structures, all living cells can be divided into two groups: eukaryotic and prokaryotic – Eukaryotic cell types - Animals, plants, fungi, protozoa, and algae – Prokaryotic cell types - bacteria & blue green algae
  3. 3. Schematic of typical animal (eukaryotic) cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough ER (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles
  4. 4. Prokaryotic Cells • much smaller (microns) and more simple than eukaryotes • prokaryotes are molecules surrounded by a membrane and cell wall. • they lack a true nucleus and don’t have membrane bound organelles like Mitochondria, Golgi complex, etc. • large surface-to-volume ratio : nutrients can easily and rapidly reach any part of the cells interior
  5. 5. Size of Bacteria • Unit of measurement in bacteriology is the micron / micrometre (µm) • Bacteria of medical importance 0.2 – 1.5 µm in diameter 3 – 5 µm in length
  6. 6. 1 micrometer (µm) = thousandth part of millimeter = 10-3 mm = 10-6 m 1 nanometer (nm) = thousandth part of micrometer = 10-3 µm = 10-6 mm = 10-9 m 1 Angstrom unit (A )= tenth part of nanometer = 10-10 m
  7. 7. Shape of Bacteria • Cocci – spherical/ oval shaped (major groups) • Bacilli – rod shaped • Vibrios – comma shaped • Spirilla – rigid spiral forms • Spirochetes – flexible spiral forms • Actinomycetes – branching filamentous bacteria • Mycoplasmas – lack cell wall
  8. 8. Arrangement of bacteria: Cocci groups of eight - SarcinaCocci in cluster - Staphylococci groups of four - TetradCoccus In pair- Diplococcus Cocci in chain - Streptococci
  9. 9. Arrangement of bacteria: Bacilli
  10. 10. Other shapes of bacteria Vibrio Spirilla Spirochetes
  11. 11. Anatomy of a Bacterial Cell
  12. 12. Anatomy of A Bacterial Cell • Outer layer - two components: 1. Rigid cell wall 2. Cytoplasmic (Cell/ Plasma) membrane – present beneath cell wall • Cytoplasm - gel-like substance enclosed within the cell membrane contains cytoplasmic inclusions, ribosomes, mesosomes and nucleoid • Additional structures - plasmid, slime layer, capsule, flagella, fimbriae (pili), spores
  13. 13. Structure & Function of Cell Components
  14. 14. CELL WALL • Outermost layer, encloses cytoplasmic membrane 1. Confers shape and rigidity 2. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape 3. 10 - 25 nm thick 4. Composed of Mucopeptide (peptidoglycan/ murein): formed by N-acetyl glucosamine (NAG) & N-acetyl muramic acid (NAM) alternating in chains, held by peptide chains.
  15. 15. • Cell wall – 5. Can not be seen by direct light microscopy and do not stain with simple stains. 6. Can be observed by plasmolysis 7. Carries bacterial antigens – important in virulence & immunity. 8. Chemical nature of the cell wall helps to divide bacteria into two broad groups – Gram positive & Gram negative 9. Gram +ve bacteria have simpler chemical nature than Gram –ve bacteria. 10. Several antibiotics may interfere with cell wall synthesis e.g. Penicillin, Cephalosporins
  16. 16. Gram positive cell wall • The Gram-positive cell wall is composed of a thick, multilayered peptidoglycan sheath outside of the cytoplasmic membrane. • Teichoic acids are linked to and embedded in the peptidoglycan, and lipoteichoic acids extend into the cytoplasmic membrane
  17. 17. Gram negative cell wall • The Gram-negative cell wall is composed of an outer membrane linked to thin single-layered peptidoglycan by lipoproteins. • The peptidoglycan is located within the periplasmic space that is created between the outer and inner membranes. • The outer membrane includes porins, which allow the passage of small hydrophilic molecules across the membrane, and lipopolysaccharide molecules that extend into extracellular space.
  18. 18. Cell Wall
  19. 19. 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
  20. 20. Cytoplasmic (Plasma) membrane • Thin layer 5-10 nm, separates cell wall from cytoplasm • Acts as a semipermeable membrane: controls the inflow and outflow of metabolites • Passage through membrane depends on: Molecular size Specific enzymes (permeases) • Composed of lipoproteins with small amounts of carbohydrates
  21. 21. Cytoplasm • Colloidal system of variety of organic & inorganic solutes in viscous watery solution • Contains: ribosomes, mesosomes, inclusions vacuoles Cytoplasm
  22. 22. Cytoplasmic Components • Ribosomes Protein synthesis 70 S • Mesosomes – 1. Multilaminated structures formed as invaginations of plasma membrane 2. Principal sites of respiratory enzymes 3. Coordinate nuclear & cytoplasmic division during binary fission 4. More prominent in Gram +ve bacteria • Intracytoplasmic inclusions Reserve of energy & phosphate for cell metabolism e.g. Metachromatic granules in diphtheria bacilli
  23. 23. Nucleus • No nucleolus • No nuclear membrane • Oval or elongated bodies generally 1 per cell • Genome – – single, circular double stranded DNA. – Haploid – Divides by binary fission Nucleus
  24. 24. Additional Organelles 1. Plasmid: • Extranuclear genetic elements consisting of DNA • Transmitted to daughter cells during binary fission • May be transferred from one bacterium to another • Not essential for life of the cell • Confer certain properties e.g. drug resistance, toxicity
  25. 25. Additional Organelles 2. Capsule & Slime layer: • Viscous layer secreted around the cell wall. • Polysaccharide / polypeptide in nature a) Capsule – sharply defined structure, antigenic in nature • Protects bacteria from lytic enzymes • Inhibits phagocytosis • Stained by negative staining using India Ink • Can be demonstrated by Quellung reaction (capsule swelling reaction) b) Slime layer – loose undemarcated secretion
  26. 26. Capsular material: • Antigenic in nature • can be demonstrated by serological methods Repeated subcultures in vitro lead to loss of capsule and also of virulence.
  27. 27. Additional Organelles 3. Flagella – • Long (3 to 12 µm), filamentous surface appendages • Organs of locomotion present in motile bacteria • Chemically, composed of proteins called flagellins • The number and distribution of flagella on the bacterial surface are characteristic for a given species - hence are useful in identifying and classifying bacteria • Flagella may serve as antigenic determinants (e.g. the H antigens of Gram-negative enteric bacteria) • Presence shown by motility e.g. hanging drop preparation
  28. 28. • Each flagellum consists of 3 parts 1. Filament 2. Hook 3. Basal body
  29. 29. Types of flagellar arrangement Polar/ Monotrichous – single flagellum at one pole Lophotrichous – tuft of flagella at one pole Peritrichous – flagella all over Amphitrichous – flagella at both poles Amphilophotrichous – tuft of flagella at both ends
  30. 30. Additional Organelles 4. Fimbriae/ Pili – • Thin, hairlike appendages on the surface of many Gram negative bacteria • 10-20µ long, acts as organs of adhesion (attachment) - allowing bacteria to colonize environmental surfaces or cells and resist flushing • Made up of proteins called pilins. • Pili can be of two types –  Common pili - short & abundant  Sex pili - small number (one to six), very long pili, helps in conjugation (process of transfer of DNA)
  31. 31. Additional Organelles 5. Spores : • Highly resistant resting stages formed during adverse environment (depletion of nutrients) • Formed inside the parent cell, hence called Endospores • Very resistant to heat, radiation and drying and can remain dormant for hundreds of years. • Formed by bacteria like Clostridium, Bacillus
  32. 32. The cycle of spore formation and germination At the beginning of spore formation, a septum forms, separating the nascent spore from the rest of the cell and all of the genetic material of the cell is copied into the newly-forming cell. The spore contents are dehydrated and the protective outer coatings are laid down. Once the spore is matured it is released from the cell. On germination, the spore contents rehydrate and a new bacterium emerges and multiplies.
  33. 33. Shape & position of bacterial spore Oval central Spherical central Oval sub terminal Oval sub terminal Oval terminal Spherical terminal Free spore Non bulging Bulging
  34. 34. Pleomorphism & Involution forms • Pleomorphism : great variation in shape & size of individual cells e.g. Proteus species • Involution forms : swollen & aberrant forms in ageing cultures, especially in the presence of high salt concentration e.g. plague bacillus • Cause – defective cell wall synthesis Involution forms can also be developed due to activity of autolytic enzymes
  35. 35. Differences between prokaryotic & eukaryotic cells Character Prokaryotes Eukaryotes Nucleus Nuclear membrane Absent Present Nucleolus Absent Present Chromosome One circular One or more paired and linear Cell division Binary fission Mitosis Cytoplasmic membrane Structure and Composition fluid phospholipid bilayer, lacks sterols fluid phospholipid bilayer containing sterols Function Incapable of endocytosis (phagocytosis and pinocytosis) and exocytosis Capable of endocytosis and exocytosis
  36. 36. Differences between prokaryotic & eukaryotic cells Character Prokaryotes Eukaryotes Cytoplasm Mitochondria Absent Present Lysosomes Absent Present Golgi apparatus Absent Present Endoplasmic reticulum Absent Present Vacuoles Absent Present Ribosomes 70 S 80 S
  37. 37. Differences between prokaryotic & eukaryotic cells Character Prokaryotes Eukaryotes Cell Wall Present Animals & Protozoans – Absent Plants, Fungi & Algae - Present Composition Peptidoglycan – complex carbohydrate Cellulose or chitin Locomotor organelles Flagella Flagella/ Cilia
  38. 38. Thank You ! DESIRE.... “ The distance between Failure and Success can only be measured by one’s Desire….! ”