Lesson 3

• Viruses


  • Lack the necessary cellular parts that can allow them to replicate independently of the host cell
  • Lack the genes and enzymes that are necessary for energy production
  • Obligate intracellular parasites
  • Acellular organisms
• Viruses

  • Possess only a single nucleic acid, either DNA or RNA, but never both
  • Outer surface is called capsid (composed of capsomeres)

  
• Virus classification

  • Naked Viruses - whose capsids are not covered by an envelope
  • Enveloped Viruses - covered with an envelope

  
• Bacteriophages


  • Are special type of viruses that primarily infect bacteria
  • They are obligate intracellular parasites
  • Similarly shaped like other viruses
  • Possess similar type of nuclei

  
• Bacteriophages play a role in the acquisition of virulence factors of certain bacteria (e.g diphtheria toxin of Corynebacterium diphtheriae) as well as in the transfer of genetic material from one bacterium to another (transduction)
• Bacteria


  • Are prokaryotic cells with majority having an outer covering called the cell wall (composed mainly of peptidoglycan)
  • Possess both the DNA and RNA
  • Possess a nucleoid instead of a true nucleus, smaller ribosomes, and lack mitochondria
• Hans Christian Gram


  • Discovered Gram Stain in 1884 where pneumonia was a big problem
  • Three causes of pneumonia; unknown (later identified as viral pneumonia, and two types of bacterial pneumonia caused by either Streptococcus pneumoniae or Klebsiella pneumoniae

  
• Bacteria can be categorized into

  • Gram-negative bacteria with cell wall (e.g., E. coli)
  • Gram-positive bacteria with cell wall (e.g., S. aureus)
  • Acid-fast bacteria with lipid-rich cell wall (e.g., Mycobacterium tuberculosis)
  • Bacteria without cell wall (e.g., Mycoplasma)
• Fungi


  • Are eukaryotic cells with an outer surface composed mainly of chitin
  • Their cell membrane is made up mostly of ergosterol
  • Possess both DNA and RNA
  • Possess a true nucleus that is enclosed by a nuclear membrane and mitochondria
• Differences between Bacteria and Fungi

  • Cell type: Prokaryotic; unicellular (Bacteria) vs Eukaryotic; unicellular or multicellular (Fungi)
  • Role in ecosystem: Can be both producers and decomposers (Bacteria) vs Mainly decomposers (Fungi)
  • Optimal pH: Neutral pH (6.5 - 7.0) (Bacteria) vs Slightly acidic (4.0 - 6.0) (Fungi)
  • Cell structures: No true nucleus and membrane-bound organelles (Bacteria) vs Possess true nucleus and membrane-bound organelles (Fungi)
  • Main component of cell wall: Peptidoglycan, except in archaebacteria (Bacteria) vs Chitin (Fungi)
  • Sterols in cell membrane: Absent except in Mycoplasma (Bacteria) vs Present (Fungi)
  • Mode of nutrition: Heterotrophic, chemoautotrophic, photoautotrophic, aerobic, anaerobic, facultative anaerobic (Bacteria) vs Heterotrophic; majority aerobic and facultative anaerobic (Fungi)
  • Reproduction: Binary fission (Bacteria) vs Sexual and asexual spores (Fungi)
• Algae


  • Are eukaryotic organisms whose outer surface consists primarily of cellulose
  • They are plant-like organisms (most of them have chlorophyll and capable of photosynthesis)
  • Unlike plants, they do not possess true roots, stems and leaves
  • Algae do not produce significant diseases in humans
• Algae

  • Diatoms - unicellular algae that inhabit both fresh - and saltwater, their cell wall contains silicone dioxide that may be utilized in filtration systems, insulation and as abrasives
  • Dinoflagellates - unicellular algae that are important members of the phytoplankton group, contribute greatly to the oxygen in the atmosphere and serve as important links in the food chain, responsible also for "red tide" and produce powerful neurotoxin which are potentially fatal disease called paralysis shellfish poisoning
• Bacterial Morphology

  • Prokaryotic, have simpler structures compared to eukaryotic organisms
  • Classified into three basic shapes: Coccus (spherical or round-shaped), Bacillus (rod-shaped), Spiral-shaped or curves
• Coccus Arrangement

  • Singly
  • In pairs (diplococci)
  • In chains (streptococci)
  • In clusters (staphylococci)
  • In groups of four (tetrad)
  • In groups of eight (octad)

  
• Glycocalyx


  • Outermost covering of some bacteria, gelatinous substances that are located external to the cell wall, composed of polysaccharide or polypeptide, or both
  • Capsule: if strongly attached
  • Slime layer: if loosely attached
• Capsule


  • Makes some pathogenic bacteria resistant to phagocytosis
  • Considered a virulence factor because it enhances the ability of bacteria to cause disease
  • Found most commonly among Gram-negative bacteria, for example, Escherichia coli, Neisseria meningitidis, Klebsiella pneumoniae, Haemophilus influenza, and Pseudomonas aeruginosa
  • Some also found among gram-positive bacteria

  
• Cell wall


  • Sometimes called the murein sacculus
  • Its principal component is peptidoglycan, which is also called murein or mucopeptide
  • Multi-layered in gram-positive bacteria and single-layered in gram-negative bacteria
  • Provides rigid support and gives shape to the bacteria
• Special Components of Gram-Positive Cell Walls

  • Teichoic acids: comprise major surface antigens of gram-positive organisms and can elicit antibody response, function for the attachment of the organism to the host cell, provide tensile strength
  • Polysaccharides: include neutral sugars such as mannose, arabinose, rhamnose, and glucosamine, also include some acidic sugars such as glucuronic and mannuronic acid
• Special Components of Gram-Negative Cell Walls

  • Outer membrane: a bi-layered structure where the inner leaflet is composed of a lipopolysaccharide (LPS), has special protein channels that allow passage of small or low-molecular weight hydrophilic substances, LPS has a complex glycolipid called lipid A, responsible for its endotoxin activity
  • Lipoprotein: functions to anchor the outer membrane to the peptidoglycan layer and stabilizes the outer membrane
  • Periplasmic space: a fluid-filled space between the outer membrane and the inner plasma membrane, contains enzymes for the breakdown of large transportable molecules into transportable ones and enzymes that serve to detoxify and inactivate antibiotics
• Gram Staining

  • Gram Positive Bacteria: Primary stain - Crystal violet, Mordant - Gram's iodine, Alcohol - Decolorizer, Safranin - Retains the primary stain, Result - Blue / Purple
  • Gram Negative Bacteria: Primary stain - Crystal violet, Mordant - Gram's iodine, Alcohol - Decolorizer, Safranin - Takes the secondary stain, Result - Red / Pink
• Flagella


  • Thread-like structures made up entirely of molecules of the protein sub-unit flagellin
  • Project from the capsule and are organs for motility
  • Classified into four types: Monotrichous (single polar flagellum), Lophotrichous (a tuft of flagella at one end), Amphitrichous (flagella at both ends), Peritrichous (flagella all around)
  • Bacteria without flagella are called atrichous
• Pili or Fimbriae


  • Rigid surface appendages found on many gram-negative bacteria
  • Fine and short in comparison with flagella
  • Their structural protein subunits are called pilin
• Gram staining(gram-negative bacteria)

  • Primary stain: Crystal violet
  • Mordant: Gram's iodine (Fixes the crystal violet on the bacterial cell wall)
  • Alcohol: Decolorizer (Removes the color violet)
  • Safranin: Will lose the primary stain and will take the secondary stain causing to appear red / pink
  • Result: Red / Pink
• Flagella


  • Thread-like structures made up entirely of molecules of the protein sub-unit flagellin
  • Project from the capsule and are organs for motility
• Types of flagella

  • Monotrichous (single polar flagellum)
  • Lophotrichous (a tuft of flagella at one end of the bacterium)
  • Amphitrichous (flagella at both ends of the bacterium)
  • Peritrichous (flagella all around the bacterium)

  
• Pili or Fimbriae


  • Rigid surface appendages found on many gram-negative bacteria
  • Fine and short in comparison with flagella
  • Structural protein subunits are called pilins
  • May function for motility or adherence to cell surface (common pili) or attachment to another bacterium during conjugation (sex pili)
• Axial filaments


  • Also called endoflagella and are found in spirochetes
  • Composed of bundles of fibrils, the structures of which are similar to flagella
  • The filaments rotate producing movement of the outer sheath of the spirochetes propelling them forward
• Microbial growth


  Increase in the number of cells rather than size
• Nutritional requirements

  • Carbon
  • Nitrogen, Sulfur, Phosphorus
  • Inorganic ions (Magnesium, Potassium, Calcium, Iron, Trace elements)
  • Growth factors (Vitamin B, Amino acids)
• Autotrophs


  Microorganisms that utilize inorganic compounds (e.g., carbon dioxide) and inorganic salts as their sole carbon source
• Heterotrophs


  Organisms that make use of organic substance like sugars or glucose as their carbon source
• Photolithotrophs and photoorganotrophs


  Derive energy from light
• Chemolithotrophs and chemoorganotrophs


  Derive energy from oxidation of inorganic substances
• Magnesium


  • Stabilizes ribosomes, cell membranes and nucleic acids, Serves as a co-factor in the activity of many enzymes
• Potassium


  • Required for the normal functioning and integrity of ribosomes and other enzymatic activities of the cell
• Calcium


  • Important component of gram-positive bacterial cell wall and contributes to the resistance of bacterial endospores against adverse environmental conditions
• Iron


  • Component of cytochrome, a component of the electron transport chain, and functions as a co-factor for enzymatic activities
• Trace elements


  Components of enzymes and functions as co-factors
• Moisture / Water


  The bacterial cell is composed mainly of water, serves as the medium from which bacteria acquire their nutrients
• microbes based on oxygen requirements

  • Aerobes: Utilize molecular oxygen for energy production
  • Obligate Anaerobes: Cannot survive in the presence of oxygen
  • Facultative organisms: Can grow and survive under both aerobic and anaerobic conditions