Microoo

• Hook


  In bacterial flagellar structure, the hook acts as a flexible coupling between the basal body and the filament. It connects the motor embedded in the cell membrane (basal body) to the long, helical tail-like filament that extends from the cell. The hook allows for the transmission of torque generated by the motor to rotate the filament, propelling the bacterium forward.
• Flagellum (plural: flagella)


  A whip-like appendage extending from the surface of some bacterial cells. It is primarily involved in bacterial motility, allowing bacteria to move toward or away from particular stimuli such as nutrients or toxins. The flagellum is composed of a filament, hook, and basal body.
• Basal body


  A structure that anchors the flagellum to the bacterial cell membrane and cell wall. It is a complex molecular machine that spans the cell envelope and serves as the motor that drives flagellar rotation.
• Bacterial flagella arrangements


  • Monotrichous
  • Lophotrichous
  • Amphitrichous
  • Peritrichous
• Monotrichous bacteria


  • Vibrio cholerae
• Lophotrichous bacteria

  • Helicobacter pylori
• Peritrichous bacteria


  • Salmonella
  • Proteus mirabilis
• Amphitrichous bacteria


  • Spirillum
• Donor Cell Formation

  1. Donor bacterial cell contains a piece of genetic material, often in the form of a plasmid

  2. Donor cell synthesizes a pilus

  3. Pilus of donor cell makes contact with recipient bacterial cell

  4. Specialized protein complex forms a channel between donor and recipient cells

  5. Donor cell transfers a copy of its genetic material into the recipient cell

  6. Transferred DNA may integrate into recipient's chromosome or exist as an extrachromosomal element

  7. Recipient cell can become a donor in subsequent conjugation events
• Capsule


  A well-organized and tightly bound layer of polysaccharides or polypeptides that surrounds the bacterial cell. Capsules are usually thicker, denser, and more tightly attached to the cell wall compared to slime layers. The main function of capsules is to provide protection to the bacterial cell from desiccation, phagocytosis, and other environmental stresses. Capsules also play a role in adherence to surfaces and tissues, and can contribute to bacterial virulence by helping pathogens evade the host immune system.
• Slime Layer


  A loosely organized and unstructured layer of extracellular polysaccharides that surrounds the bacterial cell. Slime layers are usually thinner, more diffuse, and less tightly attached to the cell wall compared to capsules. The main function of slime layers is to facilitate attachment to surfaces and the formation of biofilms.
• Outer Membrane


  The outer membrane consists of a lipid bilayer, similar to the plasma membrane, but with some key differences. The outer leaflet of the outer membrane primarily contains lipopolysaccharides (LPS), also known as endotoxins, which are complex molecules composed of lipid A, core oligosaccharides, and O antigen side chains. The outer membrane forms a selectively permeable barrier that protects the bacterial cell from various environmental stresses, such as antibiotics, detergents, and host immune defenses.
• Cell Wall


  The cell wall of bacteria is a rigid and protective structure that surrounds the cell membrane and provides structural support and shape to the bacterial cell. It plays a crucial role in maintaining cell integrity, resisting osmotic pressure, and protecting the cell from environmental stresses.
• Types of bacterial cell walls


  • Gram-positive
  • Gram-negative
• Gram-positive cell wall


  • Thick and consists primarily of a thick layer of peptidoglycan
  • Peptidoglycan forms a thick, homogeneous layer that surrounds the cell membrane
  • Peptidoglycan can constitute up to 90% of the cell wall's dry weight
  • May contain other components such as teichoic acids and proteins
• Gram-negative cell wall


  • Thinner and contains a much thinner layer of peptidoglycan compared to Gram-positive bacteria
  • Peptidoglycan layer is located in the periplasmic space, sandwiched between the inner and outer membranes
  • Peptidoglycan layer is typically only 1-2 layers thick
  • Outer membrane contains lipopolysaccharides (LPS), which are absent in Gram-positive bacteria
• Microbiology


  The science or study of organisms too small to be observed with the naked eye, i.e., not visible without the aid of instruments capable of magnification

  
• Microorganisms (microbes)


  • Eukaryotic cell types (protozoa, certain fungi, certain algae and the immature forms of multicellular parasites)
  • Prokaryotic cell types (bacteria and archaea)
  • Viruses, viroids and prions (noncellular entities)
• Microorganisms were involved in the production of wine, beer, yogurt, cheese and other fermented foods prepared by Neolithic human societies
• People "used" microbes to flavor and preserve foods, but did not know the tiny organisms were present
• Louis Pasteur


  Demonstrated that living microorganisms were responsible for fermentation
• Antone Van Leeuwenhoek


  Sometimes called the "father of microbiology" because he made his own microscopes, observed live microorganisms, and documented his findings with an established scientific organization (the British Royal Society or Royal Society of London)
• Abiogenesis (without life beginnings/origin) or Spontaneous generation


  Belief in abiogenesis (the spontaneous generation of living organisms from non-living materials)
• Belief in abiogenesis is not compatible with modern science
• Francesco Redi


  Disproved abiogenesis at the macroscopic level by demonstrating flies did not arise spontaneously from decaying meat
• Lazzaro Spallanzani


  Disproved abiogenesis at the microscopic level by sealing samples of boiled broth inside glass containers
• John Needham and Jan Baptist van Helmont


  Supported abiogenesis
• Louis Pasteur


  Credited with disproving abiogenesis of microorganisms using boiled broth samples maintained inside goose-necked flasks open to the air. Demonstrated microorganisms were present in air and developed a method for controlling them (pasteurization)
• John Tyndall


  Attempted to duplicate Pasteur's experiments with boiled broths in open flasks. He alternately boiled and cooled broths over a three-day period to kill endospores. His method was called fractional sterilization or Tyndallization
• Microbiology became a legitimate science only after the abiogenesis of microorganisms was shown to be a false concept (during the mid-1800s)
• Microorganisms do not arise spontaneously from non-living materials. Cells give rise to other cells through biogenesis
• Germ Theory


  Certain types of microorganisms can cause disease
• Before microorganisms were discovered, people associated disease with natural phenomena such as earthquakes, floods, or exposure to bad air or bad weather. Disease was also attributed to mysterious or supernatural causes, e.g., punishment for sinful behavior
• Girolamo Fracastoro (1546)


  Recorded his belief that disease was caused by tiny entities (spores) that could be passed from person to person. Without a microscope, he had no way to see these spores
• Ignaz Philipp Semelweis (1840)


  Urged doctors working in Vienna General Hospital to wash their hands between conducting autopsies and assisting women with childbirth fever
• Joseph Lister (1867)


  Pioneered the use of antiseptic techniques during surgical procedures. He washed his hands and instruments, and applied carbolic acid (phenol) to prevent infection. Lister knew about bacteria and is credited with developing the first pure bacterial cultures
• Robert Koch (1876)


  Developed a set of experimental steps (Koch's postulates) that could be used to show that a particular type of microorganism was responsible for causing a specific type of disease. Initially he demonstrated that anthrax was caused by Bacillus anthracis
• Koch's Postulates


  • The suspect causative agent must be found in every case of the disease
  • The specific type of microbe must be isolated from the infected individual and grown in a culture containing no other forms (pure culture)
  • Upon inoculation into a normal, healthy, susceptible animal, a pure culture of the microbial agent must produce the disease
  • The same type of microbe must be recovered again from the experimentally infected host
• During the "Golden Years" of microbiology (1857-1914) investigators discovered the bacterial causes of major human diseases including cholera, diphtheria, leprosy, plague, tetanus, tuberculosis and typhoid
• Richard J. Petri


  The man who developed the Petri dish