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Medical Microbiology

Medical Microbiology. Lecture 2 Dr. Dalia M. Mohsen Associate prof . of Microbiology. Functional Anatomy of Prokaryotic and Eukaryotic Cells. Lecture 2. Cell is the structural and functional unit of an organism.

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Medical Microbiology

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  1. Medical Microbiology Lecture 2 Dr. Dalia M. Mohsen Associate prof. of Microbiology Dr. Dalia Mohsen Associate prof. of microbiology

  2. Functional Anatomy of Prokaryotic and Eukaryotic Cells Lecture 2 Dr. Dalia Mohsen Associate prof. of microbiology

  3. Cell is the structural and functional unit of an organism All living cells are classified into Prokaryotic and Eukaryotic Cells, based on their structural and functional characteristics. Prokaryote comes from the Greek words for pre-nucleus. Eukaryote comes from the Greek words for true nucleus. Dr. Dalia Mohsen Associate prof. of microbiology

  4. Organisms Dr. Dalia Mohsen Associate prof. of microbiology

  5. Important • Viruses -Non-cellular elements that do not fit into any organizational scheme of living cells. (will be discussed later) Dr. Dalia Mohsen Associate prof. of microbiology

  6. Dr. Dalia Mohsen Associate prof. of microbiology

  7. Dr. Dalia Mohsen Associate prof. of microbiology

  8. PROKARYOTIC CELLS Dr. Dalia Mohsen Associate prof. of microbiology

  9. Bacterial Morphology Bacteria are unicellular. Most bacteria are 0.2µmin diameter and 2-8µm in length. Most bacteria are monomorphic – maintain a single shape. and few are pleomorphic – they can have many shapes. Ex – Rhizobium and Corynebacterium. Dr. Dalia Mohsen Associate prof. of microbiology

  10. Basic shapes of bacteria COCCI Cocci may be oval, elongated, or flattened on one side. Cocci may remain attached after cell division. These group characteristics are often used to help identify certain cocci. Cocky that remain in pairs after dividing are called diplococci. Cocci that remain in chains after dividing are called streptococci. Dr. Dalia Mohsen Associate prof. of microbiology

  11. Cocci that divide in two planes and remain in groups of four are called tetrads. Cocci that divide in three planes and remain in groups or cube like groups of eight are called sarcinae. Cocci that divide in multiple planes and form grape like clusters or sheets are called staphylococci. Dr. Dalia Mohsen Associate prof. of microbiology

  12. BACILLI Bacillus means rod shaped. Bacilli only divide across their short axis, so there are fewer groups. Most bacilli appear as single rods. Diplobacilli appear in pairs after division. Dr. Dalia Mohsen Associate prof. of microbiology

  13. SPIRAL BACTERIA Spiral bacteria have one or more twists. Vibrios look like curved rods Spirilla have a helical shape and fairly rigid bodies. Dr. Dalia Mohsen Associate prof. of microbiology

  14. Spirochetes have a helical shape and flexible bodies. • Spirochetes move by means of axial filaments, which look like flagella contained beneath a flexible external sheath. Dr. Dalia Mohsen Associate prof. of microbiology

  15. Unusual shapes Stella are star-shaped. Haloarcula, a genus of halophilic archaea, are rectangular. Dr. Dalia Mohsen Associate prof. of microbiology

  16. Streptobacilli appear in chains after division. Some bacilli are so short and fat that they look like cocci and are referred to as Coccobacilli. Dr. Dalia Mohsen Associate prof. of microbiology

  17. STRUCTURE OF A PROKARYOTIC CELL virulent factor movement attachment Dr. Dalia Mohsen Associate prof. of microbiology

  18. STRUCTURE OF A PROKARYOTIC CELL The structure is described according to the following organization • Structures, external to cell wall • Structure of cell wall • Structures, internal to cell wall Dr. Dalia Mohsen Associate prof. of microbiology

  19. Dr. Dalia Mohsen Associate prof. of microbiology

  20. Structures External To The Cell Wall • Glycocalyx • Flagella • Axial filaments • Fimbriae • Pili Dr. Dalia Mohsen Associate prof. of microbiology

  21. GLYCOCALYX(sugar coating) • The glycocalyx (capsule, slime layer, or extra cellular polysaccharide) is a gelatinous polymer. A capsule is neatly organized A slime layer is unorganized & loose • External to cell wall, composed of polysaccharide, polypeptide covering or both. • The presence of a capsule can be determined by negative staining. Dr. Dalia Mohsen Associate prof. of microbiology

  22. Capsules are important in contributing to the virulence of the bacteria. • Protect bacteria by preventing phagocytosis. • Allows the bacteria to adhere and colonize. • Important components of biofilm – • protects cell • Facilitates communication among them • Enable to survive by attaching to various surfaces • Protects cell against dehydration • Inhibit the movement of nutrients out of the cell. Dr. Dalia Mohsen Associate prof. of microbiology

  23. Capsulated bacteria – • Streptococcus pneumoniae • Klebsiellapneumoniae • Haemophilusinfluenzae • Bacillus anthracis • Streptococcus mutans • Yersiniapestis Dr. Dalia Mohsen Associate prof. of microbiology

  24. Streptococcus pneumoniae (in vivo) Dr. Dalia Mohsen Associate prof. of microbiology

  25. K. pneumoniae Haemophilusinfluenzae Dr. Dalia Mohsen Associate prof. of microbiology

  26. Long filamentous appendages consisting of a filament, hook, and basal body Made of chains of protein (flagellin) Attached to a protein hook Anchored to the wall and membrane by the basal body Semi rigid, helical structure that moves the cell by rotating from the basal body. FLAGELLA Dr. Dalia Mohsen Associate prof. of microbiology

  27. Flagella are anchored by pairs of rings associated with the plasma membrane and cell wall. Gram positive bacteria have only the inner pair of rings Dr. Dalia Mohsen Associate prof. of microbiology

  28. Flagella Arrangement Peritrichous – distributed over the entire cell Monotrichous – single flagellum at one pole Dr. Dalia Mohsen Associate prof. of microbiology

  29. Amphitrichous– flagella at both poles of cells Lophotrichous – a tuft of flagella coming from one pole Dr. Dalia Mohsen Associate prof. of microbiology

  30. Rotate flagella to run or tumble Move toward or away from stimuli (taxis) The stimuli include chemicals like oxygen, ribose, galactose – Chemotaxis. Stimuli can be light – Phototaxis. Motility Dr. Dalia Mohsen Associate prof. of microbiology

  31. Flagellar (H) protein functions as an antigen. • Flagella proteins are H - antigens - useful in distinguishing the variants within the species of gram-negative bacteria. • Example – 50 different H antigen for E. coli are identified. • E. coli O157:H7 – associated with food borne epidemics. Dr. Dalia Mohsen Associate prof. of microbiology

  32. AXIAL FILAMENTS • Also known asEndoflagella – are bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell. Dr. Dalia Mohsen Associate prof. of microbiology

  33. Spiral cells that move by means of an axial filament are called spirochetes. • Axial filaments are similar to flagella, except that they wrap around the cell. • Anchored at one end of a cell • Rotation causes cell the movement of the outer sheath that propels the spirochetes in a spiral motion. Dr. Dalia Mohsen Associate prof. of microbiology

  34. Fimbriae and pili are short, straight, thin, hair like appendages. FIMBRIAE AND PILI • Made up of protein called Pilin. • Arranged helically around a central core. Dr. Dalia Mohsen Associate prof. of microbiology

  35. Fimbriae– • Occur at poles or evenly distributed. • Number can vary from few to several hundreds • Allow attachment to surfaces and adhere to each other • Pili – • Longer than Fimbriae • Only one or two per cell • are used to transfer DNA from one cell to another by Conjugation – (sex Pili). • Involved in motility called twitching motility – short jerky intermittent movements, seen in Neisseriagonorrhoeae. • Other type of motility is gliding motility – smooth gliding movement of mycobacterium. Dr. Dalia Mohsen Associate prof. of microbiology

  36. Structure of Cell Wall • Is a complex, semi rigid structure responsible for the shape of the cell. • Surrounds the underlying, fragile plasma membrane. Dr. Dalia Mohsen Associate prof. of microbiology

  37. Functions: • Prevents osmotic lysis • Keep or protect the cell shape • Point of anchorage for flagella • In some species it has the ability to cause disease and is the site of action for some antibiotics. Dr. Dalia Mohsen Associate prof. of microbiology

  38. Composition and Characteristics • PEPTIDOGLYCAN - Main component of bacterial cell wall (also known as murein) - a polymer consisting of disaccharideN-acetyl glucoseamine(NAG) & N-acetyl muramic acid (NAM) linked by polypeptides chains. N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM) joined as in peptidoglycan Dr. Dalia Mohsen Associate prof. of microbiology

  39. Alternating NAM and NAG molecules form a carbohydrate backbone (the glycan portion). • Rows of NAG and NAM are linked by polypeptides (the peptido - portion). • The structure of the polypeptide cross-bridges may vary but they always have a tetra peptide side chain, which consists of 4 amino acids attached to NAMs. The amino acids occur in alternating D and L forms. Dr. Dalia Mohsen Associate prof. of microbiology

  40. Gram positive cell wall • consist of many layers of peptidoglycan and also contain teichoic acids. • Teichoic acids may: • bind and regulate movement of cations into and out of the cell • prevent extensive wall breakdown and possible cell lysis during cell growth • provide much of the cell wall's antigenicity Dr. Dalia Mohsen Associate prof. of microbiology

  41. Gram negative cell wall • Have a lipopolysaccharide-lipoprotein-phospholipid outer membrane surrounding a thin (sometimes a single) peptidoglycan layer. • Gram-negative cell walls have no teichoic acids. Dr. Dalia Mohsen Associate prof. of microbiology

  42. Forms the periplasm between the outer membrane and the plasma membrane. Protection from phagocytes, complement, antibiotics like penicillin, lysozyme, and other chemicals. . O polysaccharide antigen, e.g., E. coli O157:H7. Lipid A is an endotoxin – causes fever and shock Porins (proteins) form channels through membrane Dr. Dalia Mohsen Associate prof. of microbiology

  43. Dr. Dalia Mohsen Associate prof. of microbiology

  44. Dr. Dalia Mohsen Associate prof. of microbiology

  45. Mycobacteria Cell Wall Like Mycobacterium tuberculosis, Mycobacterium leprae Contains Mycolic acid layer (waxy layer) instead of Peptidoglycan layer Dr. Dalia Mohsen Associate prof. of microbiology

  46. Mycoplasmas Smallest known bacteria Lack cell walls Sterols in plasma membrane protect them from lysis. Archaea Wall-less, or Walls of pseudomurein (lack NAM and D amino acids) Atypical Cell Walls Dr. Dalia Mohsen Associate prof. of microbiology

  47. Structures Internal To The Cell Wall Plasma membrane Cytoplasm Nucleoid Ribosomes Inclusions Dr. Dalia Mohsen Associate prof. of microbiology

  48. Cytoplasm is the aqueous solution or substances inside the plasma membrane Consists of 80% water and primary proteins (enzymes), carbohydrates, lipids, many low molecular weight compounds Inorganic ions are present in higher concentration It is thick, aqueous, semitransparent, and elastic containing DNA, ribosomes and inclusions. CYTOPLASM Dr. Dalia Mohsen Associate prof. of microbiology

  49. Bacteria contains negative supercoiled single covalently closed circular chromosome (cccc) – single , long, continuous, and frequently circularly arranged thread of double stranded DNA called Bacterial Chromosome Nuclear area (nucleoid), there is no nucleus Bacteria can also contain plasmids, which are circular, extra-chromosomal DNA molecules. NUCLEAR AREA Dr. Dalia Mohsen Associate prof. of microbiology

  50. RIBOSOMES The cytoplasm of a prokaryote contains numerous 70s ribosomes; ribosomes consist of rRNA and protein. Protein synthesis occurs at ribosomes; it can be inhibited by certain antibiotics. The difference between prokaryotic (70s) and eukaryotic (80s) ribosomes allows antibiotics to selectively target the prokaryotic ribosomes while sparing eukaryotic ribosomes. Dr. Dalia Mohsen Associate prof. of microbiology

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