Transcript Infections - eacfaculty.org

Infections
Review of Microbiology
Principles of Infection
Development of Infection
Review of Microbiology
• Microorganisms
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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
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Bacteria are prokaryotes
• Have no nucleus
Most members of all kingdoms of
life on Earth
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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
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Some bacteria secrete enzymes
• These can produce damage
– Hemolysis (hemolytic strept)
– Collagenase --- aids spread
– Streptokinase– dissolves clots
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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
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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
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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!!!