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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 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 • 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 • • Bacteria are prokaryotes • Have no nucleus Most members of all kingdoms of life on Earth • 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 • 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) • 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 • 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 • 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 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) » Exp = contaminated food, bedding, soil, etc (see next slide) • 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 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 • 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 • 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 • 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) 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 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) Bacterial Spirochetes (all Gram negative) • Treponema pallidum • Causes syphilis • Borrelia burgdorferi • causes Lyme disease • Vibrio cholerae • Causes cholera --- entire small bowel gets infected 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 • 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!!!