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Infections

Infections. Review of Microbiology Principles of Infection Development of Infection. Review of Microbiology. Microorganisms Also called microbes Def = small living organisms that are too small to see with naked eye Non-pathogenic = those that do not cause disease

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Infections

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  1. Infections Review of Microbiology Principles of Infection Development of Infection

  2. Review of Microbiology • Microorganisms • Also called microbes • Def = small living organisms that are too small to see with naked eye • Non-pathogenic = those that do not cause disease • Pathogenic = those that cause disease (also called “pathogens”) • Types: • Bacteria • Aerobic • Anaerobic • Viruses • Combination of bacterial & viral properties • Chlamydiae ---Rickettsiae --- Mycoplasmas • Fungi • Protozoa • Usually called parasites

  3. Bacteria are prokaryotes Have no nucleus Most members of all kingdoms of life on Earth Bacteria Can live outside of the cell 3 basic shapes Rods or bacilli Cocci or spheres Spirals or spirochetes Anatomy Have rigid cell wall Gram stain based upon stain taken up by cell wall used to divide bacteria into 2 classes; Gram + / Gram – Cell membrane Slime layer --- on some bacteria Interferes with phagocytosis Flagella on some Pili (fimbriae) Help bacteria adhere to foreign cell/tissue Create bridge for plasmid transfer Usually in Gram negative bacteria

  4. Bacteria can secrete toxins Exotoxin Mainly Gram + bacteria Are antigenic Frequent effect = neurotoxicity Endotoxin In cell wall of Gram neg bacteria Released after bacteria dies Can cause endotoxic shock Increase in capillary permeability & get vascular collapse Some bacteria secrete enzymes These can produce damage Hemolysis (hemolytic strept) Collagenase --- aids spread Streptokinase– dissolves clots Some bacteria can form spores Usually Gram + Clostridium Gangrene, tetanus, botulism Anthrax Spores are hard to eradicate

  5. Viruses • Def : non-living infectious particle ( latin origin ; means poison) • does not fit into living category since it can’t reproduce by itself • Are obligate intracellular parasites • Characteristics • 3 parts : 1. RNA or DNA ( RNA Viruses called retroviruses ) 2. Protein coat 3. May have an outer envelope • usually viruses are species specific • Viral Multiplication ( 2 pathways) 1. Lytic Pathway = lysis of host cell to obtain material to build new viruses • everything is done in cytoplasm 2. Lysogenic Pathway = Viral DNA into host chromosome ( done in nucleus) • when DNA of host cell replicates you get copies of the viral DNA in all daughter cells • after a LATENT PERIOD the viral DNA is excised from the chromosome (see next slide)

  6. Chlamydia • Stain gram negative & act like gram neg coccoid bacteria • Exist in 2 forms • EB – elementary body • Infectious • Has cell wall & can bind to epithelium • RB – reticulate body • Non-infectious but can reproduce • Obligate intracellular parasites • Don’t require vectors for transmission • Transmitted via airborne or direct contact • 3 species of chlamydia • C. trachomatis • C. psittaci --- from birds • C. pneumoniae • Rickettsiae • Resemble tiny gram neg bacteria • Transmitted by insect vectors • Exp = rocky mountain spotted fever • Attack blood vessels & get rash with small hemorrhages

  7. Mycoplasma • Very tiny (smallest free-living organism) • Lack cell walls • They behave as parasites on the surface of host cells • They are not intracellular • Common cause of pneumonia • Fungi • Called mycotic infections • 2 types • Single-celled = yeast • Multicellular = molds • Hyphae = long strands of a fungus • Mycelium = mass of hyphae • Reproduce by budding of hyphae or spore production • Usually just affects superficial layers of epithelium • Candida normally present on skin

  8. Protozoa • Unicellular mobile eukaryotes • If • Most pathogenic protozoa in humans are parasites • Trichomonas vaginalis • Plasmodium --- causes malaria (ruptures RBC’s) • Amebic dysentery ---entamoeba histolytica • 2 forms--- • trophozoite = reproducing & invading intestinal mucosa • Cyst form = like spores, passed in feces • Worms – Helminths • Complex organisms which are parasites • Life cycle = ova, larva, adult

  9. Principles of Infection • Terms: • Epidemic • Pandemic • Endemic • Reservoir = source of the infection • The original host • Zoonosis = when an animal disease is transmissible to humans • Transmission to a new host • (1)Direct transmission • Person to person • touching • Indirect transmission • (2)Animal intermediate • Organism to person • Non-human animals --- called vectors • (3)Inanimate intermediates • Environment to person • Called fomites (non-living vectors)(see next slide) • Exp = contaminated food, bedding, soil, etc

  10. Control of infections • Key = break the cycle---- reservoir host transmission new host • Universal precautions – handle all body fluids & waste as contaminated • Methodology became law in 1992; administered by OSHA • Methods to reduce transmission • Clean environment & clothing • Sanitation = general washing & cleaning of equipment • Disinfection & antiseptics • Disinfection --- destruction of most pathogens • Exp --- chemicals, boiling, steam • Antiseptics --- chemicals applied to skin to decrease pathogens • Exp --- alcohol wipes • Sterilization ---- destruction of all pathogens

  11. Development of Infection • Course of an infection • Invasion & multiplication within host • Incubation period = time between entry & adequate numbers to give signs and/or symptoms of the disease • Prodromal period = sometimes present; consists of mild symptoms • Know something is wrong, but not what it is • Acute infection • Convalescence = recovery

  12. Local signs of infection • Classic inflammatory signs • Swelling • Redness • Heat • Pain • Exudate --- usually purulent • Systemic signs of infection • Fever • Malaise • Fatigue • Weakness • Anorexia • Aches & pains • Headaches • Joint pains

  13. Diagnostic tests for infection • Culture & staining of organisms • With sensitivity studies • Clinically = “C&S” • Blood tests • WBC count & differential • neutrophils ---- eosinophils-----basophils-----lymphocytes---- monocytes • Note:”shift to the left” • Bacterial = leukocytosis,esp neutrophils • Viral = if leukocytosis, esp lymphocytes; may get leukopenia • Acute = granulated WBC’s; Chronic = non-granulated WBC’s • Imaging tests • Lung consolidation in pneumonia • Abscesses within body

  14. Antimicrobial drugs • Antibacterial drugs • Classified: • By activity: bacteriocidal or bacteriostatic • By spectrum: narrow or broad • By mechanism: cell wall, protein synthesis, DNA replication • Key adverse effects • Secondary infections or symptoms from destruction of normal flora of the body • Allergies • Drug resistance • If properly used === cures the infection • Antiviral drugs • Do not kill the virus, but limit its replication • Thus, the disease is shortened but not cured • Antifungal drugs • Mechanism • Interfere with mitosis (griseofulvin) • Increase membrane permeability (nystatin)

  15. Disorders Caused by Pathogens Bacterial Cocci • Staphylococci • Gram positive grape-like clusters • Produce toxins • Key pathogen = S. aureus • Regular toxins ----- toxic shock syndrome • Entertoxins = gastroenteritis • Most frequent cause of nosocomial infections • Streptococci • Gram positive chains • Produce toxins • Can get delayed immune response (rheumatic heart disease & glomerulonephritis) • Enterococcus = streptococci normally living in intestines • Neisseria • Gram negative diplococci • N. gonorrhoeae • N. meningitidis

  16. Bacterial Bacilli • Gram positive(2 important genera; both form spores) • Bacillus anthracis • Causes anthrax ----- get skin & lung infections • Clostridium • C. perfringins ------- gas gangrene • C. botulinum --------- botulism • C. tetani --------------- tetanus • Gram negative • Enterics --- they reside in intestinal tract • Escherichia coli • Helicobacter pylori • Salmonella ---- food poisoning; typhoid fever • Shigella ----- dysentery • URI presentation • Hemophilis influenzae ---- pneumonia, epiglottis, meningitis • Legionella • Mycobacterium tuberculosis • Bordetella pertussis • Pseudomonas – normal contaminant of the skin (axilla & perineal)

  17. Bacterial Spirochetes(all Gram negative) • Treponema pallidum • Causes syphilis • Borrelia burgdorferi • causes Lyme disease • Vibrio cholerae • Causes cholera --- entire small bowel gets infected

  18. Small bacteria;Obligate intracellular parasites • Chlamydia • Gram negative cocci • Transmitted by airborne or contact • C. trachomatis • Conjunctivitis • STD; urethritis • Rickettsia • Gram negative coccobacilli • Involve transmission via insect vector • Causes diseases with acute onset of fever which lasts 2 weeks! • Also get characteristic rashes from damaged capillary permeability • Rocky mountain spotted fever

  19. Influenza • Etiology = RNA virus of myxovirus group • 3 key types; A, B, & C --- each with many strains • Pathogenesis • Get destruction of respiratory mucosa • Thus, prime set up for secondary bacterial infections • Key groups: infants & people over 65 • Spread person to person by respiratory droplets • Incubation = 1-4 days (short) • Vaccine available but only good for one year • Reason: virus undergoes constant antigenic changes • Course of disease = 5-7 days • New drugs --- in RCT’s (randomized controlled trials) only found they shortened course by 1 day!!!

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