bacterial morphology and classification

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This is a series of lectures on microbiology useful for undergraduate medical and paramedical students

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  • bacterial morphology and classification

    1. 1. Bacteria – Morphology & Classification Dr. Ashish Jawarkar Consultant Pathologist Parul Sevashram Hospital
    2. 2. Learning Objectives  After completing this section you should be able to perform the following objectives:  list the differences between prokaryotic and eukaryotic cell  Describe the structure of a bacterial cell and explain the function of its components  Explain why cell wall forms the basis for classification of bacteria  Explain the structural modifications (flagella) of the cell and their functional importance Dr. Ashish Jawarkar 2
    3. 3. Size of Bacteria  Unit of measurement in bacteriology is the micron (micrometre, µm)  1 micrometre (10-6)= 1/1000 mm = 1/10000 cm = 1/100000 metre  1 nanometer (10-9)= 1/1000 micrometer = 1/100000000 meter  Bacteria of medical importance  0.2 – 1.5 µm in diameter  3 – 5 µm in length Dr. Ashish Jawarkar 3
    4. 4. Dr. Ashish Jawarkar 4
    5. 5. Dr. Ashish Jawarkar 5
    6. 6. Introduction:  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, protozoans  Prokaryotic cell types - bacteria Dr. Ashish Jawarkar 6
    7. 7. Prokaryotic Cells  prokaryotes are molecules surrounded by a membrane and cell wall.  they lack a true nucleus and don’t have membrane bound organelles like mitochondria, etc.  large surface-to-volume ratio : nutrients can easily and rapidly reach any part of the cells interior Dr. Ashish Jawarkar 7
    8. 8. Anatomy of a Bacterial Cell Dr. Ashish Jawarkar 8
    9. 9. Anatomy of A Bacterial Cell  Outer layer – two components: 1. 2. Rigid cell wall Cytoplasmic (Cell/ Plasma) membrane – present beneath cell wall  Cytoplasm – cytoplasmic inclusions, ribosomes, mesosomes, genetic material  Additional structures –capsule, flagella, fimbriae (pili), spores Dr. Ashish Jawarkar 9
    10. 10. Structure & Function of Cell Components
    11. 11. CELL WALL  Outermost layer, encloses cytoplasm 1. Confers 2. 10 shape and rigidity - 25 nm thick 3. Composed of peptidoglycan Dr. Ashish Jawarkar 11
    12. 12. Cell Wall  Cell wall – 4. Chemical nature of the cell wall helps to divide bacteria into two broad groups – Gram positive & Gram negative 5. Carries bacterial antigens – important in virulence & immunity – gm –ve cell wall has lipopolysachhrides – fever and necrosis 6. Several antibiotics may interfere with cell wall synthesis e.g. Penicillin, Cephalosporins Dr. Ashish Jawarkar 12
    13. 13. 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 Dr. Ashish Jawarkar 13
    14. 14. Gram negative cell wall The Gram-negative cell wall is composed of an outer membrane linked to thin, mainly single-layered peptidoglycan by lipoproteins.The outer membrane includes porins, which allow the passage of small hydrophilic molecules across the membrane, and lipopolysaccharide molecules that extend into extracellular space. Dr. Ashish Jawarkar 14
    15. 15. 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  Composed of lipoproteins with small amounts of carbohydrates Dr. Ashish Jawarkar 15
    16. 16. Dr. Ashish Jawarkar 16
    17. 17. Other Cytoplasmic Components  Ribosomes – protein synthesis  Mesosomes – Multilaminated structures formed as invaginations of plasma membrane 2. Principal sites of respiratory enzymes 1.  Intracytoplasmic inclusions – reserve of energy & phosphate for cell metabolism e.g. Metachromatic granules in diphtheria bacilli Dr. Ashish Jawarkar 17
    18. 18. Dr. Ashish Jawarkar 18
    19. 19. Nucleus  No nucleolus  No nuclear membrane  Genome –  single, circular double stranded DNA. Dr. Ashish Jawarkar 19
    20. 20. Additional Organelles 1. Plasmid –    Extranuclear genetic elements consisting of DNA Transmitted to daughter cells Confer certain properties e.g. drug resistance, toxicity Dr. Ashish Jawarkar 20
    21. 21. Additional Organelles 2. Capsule–    Viscous layer secreted around the cell wall. Polysaccharide / polypeptide in nature Capsule – sharply defined structure, antigenic in nature • • Protects bacteria Stained by negative staining using India Ink Dr. Ashish Jawarkar 21
    22. 22. Additional Organelles 3. Flagella –  Long (3 to 12 µm), filamentous surface appendages  Organs of locomotion Dr. Ashish Jawarkar 22
    23. 23. Types of flagellar arrangement Polar/ Monotrichous – single flagellum at one pole Lophotrichous – tuft of flagella at one pole Amphitrichous – flagella at both poles Peritrichous – flagella all over Amphilophotrichous – tuft of flagella at both ends Dr. Ashish Jawarkar 23
    24. 24. Additional Organelles 4. Fimbriae/ Pili –  Thin, hairlike appendages on the surface of many Gram-negative bacteria  10-20µ long, acts as organs of adhesion Dr. Ashish Jawarkar 24
    25. 25. 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 Clostridia, bacillus Dr. Ashish Jawarkar 25
    26. 26. Differences between prokaryotic & eukaryotic cells Character Eukaryotes Nuclear membrane Absent Present Nucleolus Absent Present Chromosome Nucleus Prokaryotes One circular One or more paired and linear fluid phospholipid bilayer, lacks sterols fluid phospholipid bilayer containing sterols Cytoplasmi Structure and c Composition membrane
    27. 27. Differences between prokaryotic & eukaryotic cells Character Cytoplasm Prokaryotes Eukaryotes Mitochondria Absent Present Lysosomes Absent Present Golgi apparatus Absent Present Endoplasmic reticulum Absent Present Vacuoles Absent Present Ribosomes Present Present Dr. Ashish Jawarkar 27
    28. 28. Differences between prokaryotic & eukaryotic cells Character Prokaryotes Eukaryotes Cell Wall Present Absent Except Fungi Locomotor organelles Flagella Flagella/ Cilia Dr. Ashish Jawarkar 28
    29. 29. Dr. Ashish Jawarkar 29
    30. 30. GROWTH AND MULTIPLICATION Dr. Ashish Jawarkar 30
    31. 31. Binary Fission  DNA replication  Plasma membrane invaginate  Cell wall deposited in invaginated space  Cross wall completed  Cells separate 07.09.08 Dr. Ashish Jawarkar
    32. 32. Binary Fission  Light 07.09.08 micrograph Dr. Ashish Jawarkar
    33. 33. Binary Fission Dr. Ashish Jawarkar 33
    34. 34. Consequences of Binary Fission  Very large number of cells very fast  Mathematical progressions  arithmetic (1>2>4>6>8>10>12>14>16)  geometric(1>2>4>8>16)  exponential expression (20 > 21 > 22 >23>24)  logarithmic expression(0 >log 1>log 2>log 3>log 4) 2 2 2 2 07.09.08 Dr. Ashish Jawarkar
    35. 35. Bacterial Growth Curve Stationary phase Death phase Log phase Lag phase 1 07.09.08 5 Time (hours) Dr. Ashish Jawarkar 10
    36. 36. G: Generation time Time in minutes or hours for a population of bacteria to double in number
    37. 37. Calculation of Generation Time Log Number of Bacteria Double # cells Log phase Generation time 1 07.09.08 5 Time (hours) Dr. Ashish Jawarkar 10
    38. 38. GENERATION TIME / population doubling time  E-coli – 20 min  MTb - 20 hours  Mleprae - 20 days Dr. Ashish Jawarkar 38
    39. 39. Minimum Growth requirements  Water as a source of carbon  Nitrogen source  Inorganic salts like phosphate, sulphate, sodium, potassium, iron etc – need to be supplied in culture media Dr. Ashish Jawarkar 39
    40. 40.  Phototrophs – derive energy from sunlight  Chemotrophs – from chemical reactions  Autotrophs – synthesize organic compounds  Heteretrophs – cannot synthesize, depend on others Dr. Ashish Jawarkar 40
    41. 41. Oxygen requirement  Aerobic – V. cholera  Anaerobic - Clostridia Dr. Ashish Jawarkar 41
    42. 42. Carbon dioxide  All require  Some like Brucella, req 5-10% k/a capnophilic Dr. Ashish Jawarkar 42
    43. 43. Temperature  Mesophilic – 25-40  Psychrophilc - <20  Thermophilic – 55-80  Except thermophilic, most die at 50-60, k/a thermal death point Dr. Ashish Jawarkar 43
    44. 44. Other factors  Moisture  pH Dr. Ashish Jawarkar 44

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