Lesson 5

• Pathophysiology | AY 2023-2024
• James A. de la Cruz, RMT, MD | June 18, 2024
• Infection and Pathogens
• Lecture 5
• Microbiology


  The study of microorganisms or microbes, very small living forms that are visible only with a microscope
• Microorganisms


  • Bacteria
  • Fungi
  • Protozoa
  • Viruses
• Prokaryotes


  Unicellular organisms with complex cell wall structure having no distinct nuclear structure and other organelles
• Eukaryotes


  Multicellular organisms found in plants and animals with distinct nucleus
• Pathogens


  Disease-causing microbes often referred to as "germs"
• Non-pathogens


  Microorganisms that do not usually cause disease (sometimes called "commensal")
• Invasion


  Successful entry of the microorganisms into the host
• Types of Bacteria


  • Bacilli
  • Spirals (spirochetes)
  • Cocci
• Bacterial Arrangements


  • Diplo-
  • Strepto-
  • Staphylo-
  • Tetrad
  • Palisade
• Gram staining


  Method of bacterial classification based on the reaction with Gram's stain of the cell wall components
• Gram staining process


  • Crystal violet
  • Gram's iodine
  • Alcohol
  • Safranin
• Gram positive bacteria


  • Rigid external layer conferring shape and pathogenicity
  • Capsule (slime layer) functions to resist phagocytosis as well as adhesion to surfaces
  • Flagella for motility and escape
  • Pili and fimbriae for attachment and genetic variation
  • Plasmid containing genetic information conveying drug resistance
• Gram negative bacteria


  • Rigid external layer conferring shape and pathogenicity
  • Capsule (slime layer) functions to resist phagocytosis as well as adhesion to surfaces
  • Flagella for motility and escape
  • Pili and fimbriae for attachment and genetic variation
  • Plasmid containing genetic information conveying drug resistance
• Exotoxins


  Found in Gram positive organisms with variety of effects - interfering with nerve conduction, may stimulate the vomiting center, and some stimulate antibody or antitoxin production
• Endotoxins


  Found in Gram negative organisms that are released after the bacteria die and cause severe effects - fever, increased capillary permeability, shock, etc.
• Enzymes


  Digest cellular components (e.g., collagenase, streptokinase)
• Endospores


  Latent form of the bacterium with a coating that is highly resistant to heat and other adverse conditions
• Binary fission


  Division of the cell that produces two daughter cells identical to the parent bacterium
• Rate of bacterial replication varies from a few minutes to many hours, depending on the particular microbe (large colony formed for fast growers)</b>
• Bacterial replication is affected by nutrients, oxygen, pH, temperature, and waste buildup
• Viruses


  Very small obligate intracellular parasite that requires a living host cell for replication
• Viral components


  • Protein core: RNA or DNA
  • Envelope: enveloped or naked
  • Strands: single or double stranded
• Viruses are typically designated based on "appearance" for convenience but most viruses do not have specific shapes
• Viral pathogenesis


  • Viruses remain in a latent stage; they enter host cells and replicate slowly or not at all until sometime later
  • Viruses can insert their capsid proteins into the cell membrane of the host
  • Frequently one type of virus exists in many similar forms or strains, and viruses tend to mutate, or change slightly, during replication (e.g., Influenza) with factors that make it difficult for a host to develop adequate immunity
  • Viruses hide inside human cells
  • Certain intracellular viruses may also alter host cell chromosomes
• Chlamydia, Rickettsia, and Mycoplasma


  • Chlamydiae: considered primitive forms related to bacteria that lack many enzymes for metabolic processes
  • Rickettsiae: tiny Gram-negative obligate intracellular bacteria that are transmitted by insect vectors, such as lice or ticks
  • Mycoplasma: common cause of (atypical) pneumonia and are cell wall-less organisms and appear in many shapes
• Fungi


  • Ubiquitous organisms on animals, plants, humans, and foods and are often found on dead organic material
  • Classified as eukaryotic and consist of single cells or chains of cells
  • Forms: (unicellular) yeast or (multicellular) mold, or dimorphic fungus
  • Can grow on a wide range of environmental conditions (common food contaminants)
  • Considered beneficial because they are important in the production of yogurt, beer, and other foods, as well as serving as a source of antibiotic drugs
• Fungal structures


  • Hypha (plural: hyphae) - structural units of fungi (septate or aseptate)
  • Mycelium: mass of hyphae (aerial or vegetative)
  • Reproduction: budding, extension, spore formation
  • Spores: structures produced by fungi that can spread easily through the air, resistant to temperature change and chemicals, and can stimulate an allergic reaction in humans when inhaled
  • Asexual spores formed through mitosis and are identical to parent organism; sexual spores are formed by meiosis
• Fungal classification


  • Yeast: unicellular organisms that are round to oval (2 to 60 µm), reproduce asexually by blastoconidia formation (budding) and sexually by the production of ascospores or basidiospores
  • Molds: multicellular organisms, basic structural units: hyphae, coenocytic (sparsely septate), dematiaceous, hyaline, mycelium: loose network of hyphae
• Fungal classification (clinical)


  • Superficial mycoses: keratinized skin layer
  • Cutaneous mycoses: involves hair, skin, nails (dermatophytes)
  • Subcutaneous mycoses: limited in the subcutaneous tissues without dissemination to other sites
  • Systemic mycoses: widely disseminated infection in different organs and systems
• Protozoa


  • More complex eukaryotic unicellular organisms usually motile, lacks cell wall
  • Occur in a number of shapes
  • Most live independently, some live on dead organic matter, and others are living in or on another living host (parasite)
  • Forms: trophozoite, cyst
  • Part of the bigger group of parasites, together with metazoans (trematodes, nematodes, cestodes, helminths)
• Protozoa types


  • Apicomplexans
  • Flagellates
  • Ciliates
• Helminths


  • Non-microscopic worms
  • Multicellular, eukaryotic organisms divided based on physical characteristics
  • Length: may be very small, barely visible, or up to 1 meter in length
  • Life cycle consists of at least three stages - ovum (egg), larva, adult
  • Common methods of invasion: ingestion of contaminated food or water, direct entry through the skin or be transmitted via vectors
  • Habitat: intestine, lung, blood vessels during parts of their life cycle
• Prions


  • Protein-like agents that are transmitted by consumption of contaminated tissues such as muscle or the use of donor tissues contaminated with the protein
  • Prion: an abnormal molecule that is transmissible in tissues or blood of animals or humans; induces proteins within the brain of the recipient to undergo abnormal folding and change of shape which renders the protein molecule nonfunctional and causes degenerative disease of the nervous system
  • Example: Creutzfeldt-Jakob disease, variant Creutzfeldt-Jakob disease, and bovine spongiform encephalopathy (BSE)
• Infection


  Occurs when a microbe or parasite is able to reproduce in or on the body's tissues
• Infectious diseases


  May occur sporadically in single individuals, localized groups, and epidemics or worldwide pandemics
• Factors affecting infection


  Agent, host, environment