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1 introduction bacterial cells
This document provides an introduction to the field of medical microbiology. It discusses important events in the history of microbiology including the discovery of microorganisms by Anton van Leeuwenhoek in 1674. It also outlines Koch's postulates for identifying pathogenic microbes and describes the main branches of medical microbiology. The document then examines the structures and characteristics of prokaryotic and eukaryotic cells, highlighting differences between bacteria, archaea, and eukaryotes. It provides details on bacterial cell structures including the cell wall, cell membrane, flagella, pili, and endospores. The principles of staining bacteria and classifying them are also summarized.
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1 introduction bacterial cells
- 1. Medical Microbiology: Introduction Dr. Md.Abdullah Yusuf Assistant Professor, Dept. of Microbiology National Institute of Neurosciences & Hospital Dhaka, Bangladesh Email: ayusuf75@yahoo.com
- 2. Learning Objectives Introduction andhistory of Microbiology • Important events of history • Koch’s postulates • Branches of Medical Microbiology • Role of Microbes in environment & medical science
- 3. Important events ofhistory • Dutch Biologist “Anton Van Leeuwenhock” discovered “animicules” in a drop of water by his simple microscope in 1674 • Otto Muller (Danish biologist) organized bacteria into genus and species in1774 • In 1840, Friedrich Henle (German pathologist) proposed germ theory of disease
- 4. Conti… • Robert Koch –Father of medical Microbiology • Luis Pasteur (Father of Modern Microbiology) – identified causative agent of anthrax, rabies, plague, cholera and tuberculosis • Discovery of penicillin – 1928 (Alexander Flemming) • Discovery of sulphanilamide – 1935 (Gerhard Domagk’s) • Discovery of streptomycin – 1928 (Selman Waksman)
- 5. Koch’s postulates 1. Thecausative (etiological) agent must be present in all affected organisms – but absent in healthy individuals 1. The agent must be capable of being isolated and cultured in pure form 2. When the cultured agent is introduced to a healthy organism, – the same disease must occur 1. The same causative agent must be isolated again from the affected host
- 6. Limitation of Koch’sPostulate • Genetic Diseases • Auto-immune Diseases • Non-culturable microbial diseases
- 7. Branches of MedicalMicrobiology • Bacteriology – General – Systemic • Virology – General – Systemic • Parasitology – Protogoology – Helminthiology • Mycology • Immunology
- 8. Difference between VirusAnd Bactria • Structure • Nucleic Acid • Type of Nucleus • Ribosomes • Nature of Outer Surface • Motility • Method of Replication
- 9. Eukaryotes and Prokaryotes •Properties • Differences • examples
- 10. What is bacterium? •Prokaryotic cells – Pro means primitive – Karyote means nuceus • Multiply by binary fission – 1divide to 2 • Devoid of chlorophil • ** single cell, living being, microscopic entity but fantastic in structural organization, reproduction, metabolism and function
- 11. Eukaryotes • Eu meansTrue (normal) • Karyote means nucleus • Much larger than most prokaryotes • Have subcellular, membrane-bound organelles • Includes all “higher" plants and animals • Microbiology includes – Fungi – Protozoa – Algae – Multicellular Organisms (helminthes)
- 12. Fungus • Eukaryotic organism •cell walls contains Chitin • Molds are multicellular – masses of mycelia – composed of filaments called hyphae • Yeasts are unicellular
- 13. Protozoa • Eukaryotes • NoCell Wall • Surround and absorb food • May be motile via – Pseudopods – cilia, or – flagella
- 14. Algae • Eukaryotes • Cellulosecell walls • Use photosynthesis for energy • Produce molecular oxygen and organic compounds
- 15. Virus • Acellular • Consistof DNA or RNA • Core is surrounded by a protein coat • Coat may be enclosed in a lipid envelope • Viruses are replicated only when they are in a living host cell • Living
- 16. Multicellular- helminthes • Eukaryote •Multicellular animals • Parasitic flatworms and round worms are called helminths • Microscopic stages in life cycles
- 17. Characteristics of Prokaryotes Nuclearlevel • Absence of – nuclear membrane – Nucleolie – Nucleoplasm – paired multiple chromosome – centriole
- 18. Conti.. Cytoplasmic level • Absenceof membrane bound organelles – Mitochondria – endoplasmic reticulum – golgi complex – Microtubules – Microfilaments
- 19. Conti.. • Presence of –Ribosome – Plasmid • No protoplasmic streamming in the form of Brownian movement and Tyndall phenomena • No change in definite shape and formation of pseudopodia
- 20. Characteristics of prokaryotes(Structural) Cell coverings (cell envelope) • Innermost layer – bilaminar phospholipid + Lipoprotein – cytoplasmic membrane (fluid stage) without any sterol • Two membrane in Gram negative bacteria • Condensation at some points forming mesosome
- 21. Conti… 2) Outer toCell Membrane – cell wall containing specialized unique chemicals called peptidoglycan 3) Outer to Cell Wall – investing layer either capsule/glycocalyx/slime layer 4) S layer – Single type protein lattice outer to CW
- 22. Characteristics of Prokaryotes •No genetic exchange during chromosome replication • Show secretory and excretory activities • Show chemical selectivity, motility and alteration of life stage (spore) • Wide range of temperature and pH tolerance • Heterogenous nutritional requirements and host specificity • Can produce self protective molecule bacteriocin • Become infected by particular virus • Can acquire extrachromosomal DNA (plasmid)
- 23. Difference Between Eukaryotesand Prokaryotes • Nature of Nucleus • Mitotic Division • Presence of histones in DNA • Membrane bound Organelles • Size of Ribosomes • Peptidoglycan in Cell Wall
- 24.
- 25. Bacterial cells • essentialstructures – chemical composition – Organization – Functions • non-essential structures – chemical composition – Organization – Functions
- 26. Structures of bacteria •Essential Structures (maintain viability) – Cell Wall – Cell Membrane – Mesosome – Ribosome – Nucleoid – Periplasm
- 27. Structures of bacteria •Non-essential Structures (viability is not affected in their absence) – Flagella – fimbria (pili) – Capsule – Glycocalyx – slime layer – Plasmid – spore
- 29. Cell wall • Component –peptidoglycan (PG) – Teichoic acid – teichorunic acid – Polysaccharides – LPS – Lipoproteins • PG backbone: NAG and NAM • Tetrapeptide side chains attached to NAM • Interpeptide bridge
- 30. Conti… • Function – osmoticprotection – integrity of cellular structures – virulence factors – Fully permeable to ions, aminoacids and sugars – makes it rigid – determines shape – Acts as antigen – Used as serological diagnosis
- 31.
- 32. Gram positive cellenvelope • Covalently bound to the thick peptidoglycan are – teichoic acid (their backbones are usually phosphorus containing polymers of ribitol or glycerol) or – teichuronic acid (glucuronic acid- containing polysaccharides • negatively charged molecules concentrate metal ions from the surroundings
- 33. Conti… • Teichoic acidscan also direct autolytic enzymes to sites of peptidoglycan digestion (autolysis). • This is needed to insert sections of cell wall for growth and division. • Lipoteichoic acid is primarily associated with the cell membrane.
- 34. The Gram negativecell envelope • Covalently linked to the thin peptidoglycan is the Braun lipoprotein which binds the outer membrane to the cell wall. • Like other membranes it contains proteins and phospholipids. • Unlike other membranes it contains lipopolysaccharide
- 35. Conti… • Lipopolysaccharide – helpsto provide a permeability barrier • LPS consists of three regions – an outer O antigen – a middle core – an inner lipid A region • core contains several sugars – lipid A contains β hydroxyfatty acids (uncommon in nature) – The molecule displays endotoxin activity
- 36. Conti… • Porins inthe outer membrane form channels to allow passage of small hydrophilic nutrients (such as sugars) through the outer membrane.
- 37. Cell membrane • Phospholipidbilayer – Except triple layer in Mycoplasma • Interspersed with lipoprotein • Selectively permeable
- 38. Cell Membrane • Functions –Transport – Synthesis – Excretion – Secretion – Metabolism – division by mesosome
- 39. Nucleoid • Double strandedcoiled helical DNA molecule – remain in a single chromosome • no introns • no non-coding sequences • no regulatory sequence • no long terminal repeats (LTRs) • Operon present
- 40. Nucleoid • Function – bearsgenes and genetic characters – maintain metabolism
- 41. Ribosome • 70 sin sedimentation co-efficient • Aggregated • Function – Protein Synthesis
- 42. Non-essential structures • Flagellum/-a(long whip like) – Filamentous Protein Appendages – Composed of protein as flagellin unit – Arise from cytoplasmic membrane – Account for most bacterial motility – “Run and tumble” – Chemotaxis, phototaxis, aerotaxis, and magnetotaxis – Antigenic structure Fig 3.42
- 44. Non-essential structures Pilus/-i • Thinhair like appendages • Composed of protein as pillin subunit • Arise from cytoplasmic membrane • Function – Attachment – Conjugation – Acts as virulence factors – Antigenic
- 45. Capsule/Glycocalyx • External surfacelayer composed of polysaccharides Except – Polypeptide in Bacillus – Hyaluronic acid for Streptococci • Gel like • Forming either capsule (compact, complete and tight investing) or slime layer (loose meshwork) • Functions – prevent phagocytosis – Attachment of bacteria – Acts as Antigen
- 46. Plasmid • Extra-chromosomal Doublestranded Circular DNA • Independent of replication • Types – Transmissible – non-transmissible • Function – Carries gene for its own replication – Carries gene antibiotic resistance factors – Carries gene Proteins & toxin
- 48. Endospores • Highly resistantstructures formed at adverse environment • Composition – Bacterial DNA – small cytoplasm – cell membrane – Peptidoglycan – very little water – thick keratin like coat
- 49. Endospores • Highly resistantto – heat, moisture, chemicals, radiation and antibiotics • Special component – calcium salt of Dipicolinic acid • No metabolic activities, remain dormant for many years • Two events: sporulation and germination
- 50.
- 51.
- 53. Classification of bacteria •Basis of Classification • differences between Gram positive and Gram negative bacteria • atypical characters of bacteria in relation to staining
- 54. Basis of Classification •Morphological Classification • Staining Properties • Thickness of Wall • According to Motility
- 55. Morphological Classification Morphology ofBacteria • Cocci – rounded or oval (Staphylococcus) • Bacilli – elongated rod like (Esch.coli) • Vibrio (from vibration) – coma shaped (Vibrio cholerae) • Spiral bacteria – long slender curved body with wave like spiral (Spirillum minus, Helicobacter pylori)
- 56. Others Shapes • Cocco-bacillus –longer than coccus, shorter than bacillus (Bordetella, Brucella) • Filamentous – long curved body like ribbon with branching (Actinomycetes, Nocardia)
- 62.
- 63. Thickness of Wall •Rigid thick wall Bacteria – Free-Living (Extracellular) – Non-Free Living (Obligate Intracellular) • Flexible thin walled Bacteria – Treponema – Borrela – Leptospira • Wall-less Bacteria – Mycoplasma – Ureaplasma
- 64. Rigid thick wallBacteria • Free-Living (Extracellular) – Gram Positive – Gram Negative – Acid-Fast • Non-Free Living (Obligate Intracellular) – Rickettsia – Chlamydia
- 65. Staining Properties • GramPositive • Gram Negative • Acid-Fast Bacteria
- 66. Gram Positive Bacteria •Cocci – Streptococcus – Staphylococcus • Bacilli – Spore Forming • Bacillus – Non-spore forming • Clostridium • Corynebacterium • Listeria
- 67. Gram Negative Bacteria •Cocci – Neisseria gonorrhoae – Neisseria meningitidis • Bacilli – Enterobacteriaceae – Non-Enterobacteriaceae
- 68. According to Motility •Motile – Flagellated Bacteria – Non-Flagellated Bacteria • Non-Motile – All Cocci
- 69. Bacillus with peritrichousflagella
- 70. Morphological study ofbacteria • Staining • Motility test
- 71. Staining Theoretical approach • Types •Laboratory procedures • findings of – Gram’s – Zeihl-neelsen (Z-N) – Albert’s staining
- 72. Types of Staining •Simple Staining • Differential Staining • Special Staining
- 73. Types of Staining SimpleStaining • using a single dye – methylene blue – Leishman
- 74. Types of Staining DifferentialStaining • using primary and counter dye • performing a step of decolourisation • to see differential characters of bacteria – Gram’s stain – Ziehl-Neelsen stain – Albert stain
- 75. Types of Staining SpecialStaining • to see unique property of particular bacteria – Fluorescense stain
- 76. Gram’s staining • Namedaccording to inventor Christian Gram • Based on the property of bacterial cell envelope • stained at first by a primary dye & mordanted • Decolorized by acetone or alcohol • Counter stain is added • Gram positive bacteria – can resist decolourisation and retain the primary dye • Gram negative bacteria – can not resist decolourisation and take the counter dye
- 77. Gram Positive Bacteria •Thick layer of Peptidoglycan • Negatively charged teichoic acid on surface • Polysaccharide
- 78. Gram Negative Bacteria •Cell wall much more complex • Thin peptidoglycan layer, filled and surrounded with periplasm (protein rich gel-like fluid) • Unique outer membrane on top – Bilayer, yet outer layer is LPS layer (lipid A and O specific polysaccharide) – LPS acts as endotoxin (lipid A) • Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier. Fig 3.34
- 79. Atypical cell envelope •Acid-fast and related bacteria – Mycobacteria – Nocardia • Presence of Mycolic acids – long, branch chained fatty acids
- 80. Gram un-stainable cellwall • Atypical peptidoglycan • Spirochaetes, Mycobacterium, – High lipid content – Tight fluid mosaic
- 83.