TOB

• Infection


  Entry into and multiplication of an infectious agent (pathogen) in the tissues of the host resulting in tissue damage/injurious effects
• Primary infection


  Acute infection that causes initial illness
• Secondary infection


  Caused by opportunistic pathogen as a result of primary infection e.g. (HIV) AIDS → Candida albicans mycosis
• Subclinical infection


  Does not cause noticeable illness, person is a carrier (e.g. Hepatitis A)
• Kinds of Infectious Agents


  • Prions
  • Viruses
  • Bacteria (Prokaryotes)
  • Fungi (Eukaryotes)
  • Parasites (Eukaryotes)
• Prions


  • Particles of protein, no nucleic acid
  • Accumulate in nervous tissue and brain tissue
  • Are not visible microscopically and highly resistant to destruction
  • Cause degenerative disease in the central nervous system (e.g., mad cow Bovine spongiform encephalopathy"BSE", scrapie of sheep, disease, Parkinsons disease)
• Viruses


  • Protein coat surrounding nucleic acid core
  • Lack of enzymes necessary for metabolism
  • Insert their genome into a host cell's DNA
  • Use that cell's metabolic machinery to make new viruses
• Bacteria (Prokaryotes)


  • Cells without membrane-bound organelles
  • Can live independently
  • Use infected organism for food and shelter
• Fungi (Eukaryotes)


  • Most require a cooler temperature than human core body temperature
  • So most infections are on the surface of the body
• Parasites (Eukaryotes)


  • Protozoa: Malaria, Leishmania, giardiasis, Toxoplasma
  • Helminthes: Nematodes (roundworms), Cestodes (tapeworms), and Trematodes (flukes)
  • Arthropods: ticks, mosquitoes, fleas
• Differences Between Eukaryotic and Prokaryotic Cells


  • Nucleus: Absent in Prokaryotes, Present in Eukaryotes
  • Membranous Organelles: Absent in Prokaryotes, Present in Eukaryotes
  • Cell Wall: Chemically complex in Prokaryotes, Simple when present in Eukaryotes
  • Ribosomes: Smaller (70S) in Prokaryotes, Larger (80S) in Eukaryotes
  • DNA: Single circular chromosome in Prokaryotes, Multiple linear chromosomes (histones) in Eukaryotes
  • Cell Division: Binary fission in Prokaryotes, Mitosis in Eukaryotes
• Tissue Classification


  • Epithelial tissue
  • Connective (Support) tissue
  • Muscle tissue
  • Nervous tissue
• Gram stain


  Allows us to detect and begin to classify most bacteria
• Acid fast stains


  Allow us to detect the bacterial causes of tuberculosis and leprosy
• Both Gram and acid fast staining methods are applied millions of times every day to help in the diagnosis and treatment of infection
• Bacterial Structure


  • Shape: cocci, rods/bacilli (note arrangements), coccobaccilli
  • Variations: curved, spiral, filamentous
  • Internal structures: Spores, inclusion granules
  • External structures: fimbriae/pili, flagellae, capsule
  • The cell envelope
• Common Arrangements of Cocci

  • Inclusion granules
  • Spores
  • Capsule
  • Pili
  • Flagellae
• Other cell envelope types (not visualized with Gram stain)


  • Mycobacteria: Acid Fast Stain (AFBs)
  • Mycoplasmas: No peptidoglycan
  • Too small: rickettsia, chlamydia
• Components of Bacterial Cell Envelope


  • Glycolipids
  • Mycolic Acid
  • Arabinogalactan
  • Peptidoglycan
  • Plasma Membrane
• Leprosy


  A chronic infectious disease that primarily affects the peripheral nerves, skin, upper respiratory tract, eyes, and nasal mucosa
• Acid Fast Stains


  • Ziehl-Neelsen
  • Fluorescent
• Acid Fast Smears


  • Rapid but relatively insensitive
  • +ve AFB smear = infective patient with TB
• Clinical importance of bacterial cell walls

  • Detection and diagnosis via Gram and Acid fast stains
  • Endotoxin effects (Gram negative LPS)
  • Bacterial antigens- important in virulence and immunity
  • Target for antibiotics (site of action of some antibiotics)
• Antibiotics targeting bacterial cell walls


  • Beta-lactams (penicillllins and cephalosporins)
  • Glycopeptides
  • Isoniazid (Tubercullosis)
• Phases of Bacterial Growth Curve


  • Lag phase
  • Log OR Exponential phase
  • Stationary phase
  • Phase of Decline
• Colonies


  A biofilm is an aggregate of microorganisms in which cells are stuck to each other and/or to a surface
• Steps in biofilm formation

  • Adhesion to surface
  • Excretion of glycocalyx (glue like. Self produced polymeric matrix)
  • Growth of bacteria within glycocalyx, expansion of biofilm
  • In each step bacteria may recruit different components and molecules including flagella, pili, DNA and polysaccharides
• Requirements for Bacterial Growth


  • Specific Energy source
  • Specific Building blocks
  • Specific Atmosphere
• Bacterial Growth Atmospheres


  • Aerobes – require O2 for growth
  • Anaerobes – grow in the absence of O2 & may even die on exposure to O2
  • Microaerophilic – grow best in the presence of low oxygen levels
  • Facultative anaerobe – aerobic but can also grow in the absence of O2
• Diseases and Associated Organisms


  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Group B streptococci
  • Streptococcus pneumoniae
  • Neisseria meningitidis
  • Neisseria gonnorrhoeae
  • Clostridium perfringens
  • Clostridium difficile
  • Mycobacterium tuberculosis
  • Mycobacterium leprae
  • Escherichia coli
  • Salmonella spp.
  • Shigella
• Cartilage


  A special type of connective tissue with a firm, pliable matrix that can resist mechanical stress and act as a shock absorber
• Almost all bones first take form as cartilage

  
• Most cartilage is destroyed and replaced by bone in the prenatal or early post-natal period
• In many bones, growth in length depends on continued growth of cartilage (epiphyseal cartilage or growth plates) until growth in height ceases

  
• Types of cartilage based on anatomical distribution and function

  • Articular cartilage
  • Costal cartilage
  • Cartilage in the air passages
  • Cartilage in the ear and nose

  
• Articular cartilage


  • Allows joint movement with less friction and absorbs some shock at joints during motion
• Costal cartilage


  • Contributes to the elasticity of the thoracic wall

  
• Cartilage in the air passages


  • Allows them to remain open during respiration
• Cartilage in the ear and nose

  • Helps to retain shape and allows bending
• Cartilage composition


  Cells, fibers, and ground substance. The extracellular matrix predominates and determines cartilage's mechanical properties. Type II collagen is a characteristic cartilage matrix component.