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Microbes and diseases: what to study-1. 1. Causative microbe: name, morphology (shape, size, Gram stain, etc.), physiology (aerobe, anaerobe, etc) and some info on classification (what's it related to?)

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microbes and diseases what to study 1
Microbes and diseases: what to study-1
  • 1. Causative microbe: name, morphology (shape, size, Gram stain, etc.), physiology (aerobe, anaerobe, etc) and some info on classification (what's it related to?)
  • 2. Pathogenesis and clinical disease:  what disease does it cause (signs and symptoms) and how does it do it (capsule, toxins..)?
  • 3. Transmission and epidemiology: how do you get the disease?
microbes and diseases what to study 2
Microbes and diseases: what to study-2
  • 4. Diagnosis: How does the lab usually identify the causative agent?
  • 5. Treatment: antibiotics prescribed (or not- no cell wall, no penicillin) or other treatment (oral rehydration therapy for cholera).
  • 6. Prevention and control (stop the spread; condoms, kill urban rats..)
significant diseases of past
Significant diseases of past
  • Scarlet fever
  • Diphtheria
  • Leprosy
  • Plague
  • Typhus
  • Smallpox
  • Polio
streptococci g cocci
Streptococci: G+ cocci
  • Genera: Streptococcus and Enterococcus
  • Aerotolerant anaerobes, catalase negative
    • Grow in chains, pairs
    • Strep: Lancefield groups, viridans, S. pneumoniae
  • Group A strep: S. pyogenes
    • Pharyngitis, scarlet fever, pyoderma, erysipelas, TSS, necrotizing fasciitis
    • Sequelae: rheumatic fever and glomerulonephritis
  • Group B strep: S. agalactiae
    • Infects newborns during birth, major neonatal dis.
characteristics of streptococcal infections
Characteristics of Streptococcal infections



virulence factors etc
Virulence factors, etc.
  • S. pyogenes (“pus-producing”)
    • M protein and capsule: avoids phagocytosis
    • Streptokinase, streptolysins for escape & attack
    • Pyrogenic erythrotoxins (SPEs)
      • at least 3 different types
      • Cause scarlet fever: fever, rash; toxic shock
    • Beta hemolytic on blood agar
corynebacterium g rod
Corynebacterium: G+ rod
  • Found on humans, animals, plants
    • Normal microbiota, opportunists,& pathogens
  • C. diphtheriae: cause of disease diphtheria
    • Colonizes the throat, inflammation, fever, and pseudomembrane, release of toxin
      • Pseudomembrane can block throat
    • Toxin inhibits protein synthesis, kills cells locally
      • Toxin diffuses, kills heart and nerve cells
    • Antitoxin, antibiotic treatment
    • Vaccination (DPT); humans are only host.
mycobacterium g rods
Mycobacterium: G+ rods
  • Many non-pathogenic species, most disease: M. tuberculosis and M. leprae
    • M. avium-intracellulare: environmental source of lung disease (like TB) in AIDS patients
    • Mycolic acids as part of complex cell wall
      • Protects against desiccation
      • Protects against destruction by phagocytes
      • Requires acid-fast staining
    • Generally grow very slowly (chronic illnesses)
    • Can grow intracellularly
acid fast stain of mycobacteria
Acid Fast stain of Mycobacteria


m leprae
M. leprae
  • Cause of Hansen’s disease, aka leprosy
  • Slow growing, likes it cool; armadillos as model
  • Grows in peripheral nerve and skin cells
    • Numbness is characteristic of disease
  • Tuberculoid vs. lepromatous leprosy
    • Mild, severe, respectively, depending on cell mediated immune response.
    • Numbness vs tissue destruction
  • Spread mostly by direct contact
  • Treatable with antibiotics, but long term
gram negative rods and cocci
Gram negative rods and cocci
  • Endotoxin: Lipid A, the superantigen
    • Part of LPS of the Gram negative outer membrane
    • Causes an over-stimulation of macrophages with production of various cytokines
    • Fever, vasodilation, inflammation, shock, and disseminated intravascular coagulation
  • While Gram negative pathogens can have other virulence factors (capsules, fimbriae, exotoxins), all have endotoxin and are thus dangerous.
  • http://www.textbookofbacteriology.net/endotoxin.html
truly pathogenic enterics 3
Truly pathogenic enterics-3
  • Yersinia: Y pestis is cause of plague, other species cause food-borne infections
  • Plague: 3 cycles: sylvan, urban, and human
    • endemic in sylvan cycle; mixing of woodland and urban rodents brings urban cycle, fleas jump from dying rats to humans.
    • Infection leads to large swollen lymph nodes: buboes
      • Bubonic plague, with high fever.
      • Septicemic plague: with DIC, bruising (black death)
        • Raises mortality from75% to near 100%
      • Pneumonic: coughed out and spread human to human
        • 100% mortality
the s f earthquake and plague
The S.F. earthquake and plague

http://library.thinkquest.org/03oct/00904/images/sanf.jpg http://www.cdc.gov/ncidod/dvbid/plague/plagwest.htm

  • Gram negative, very small, obligate parasites
    • Leaky membranes?
  • Most diseases spread by vectors
  • Rickettsiae infect endothelial cells lining blood vessels, avoid digestion in lysozome
    • Have LPS, generate fever
    • Damage to capillaries produces spots, rashes
    • Damage to vessels deprives organs of oxygen
rickettsial diseases
Rickettsial diseases
  • R. rickettsii: Rocky mountain spotted fever
    • Spread by tick bite; rodents are the reservoir
    • Most common through southeast, mid-south
  • R. prowazekii: epidemic typhus
    • Humans primary host; vector is the louse
    • Disease spread in crowded, unhygienic conditions
  • R. typhi: murine/endemic typhus
    • present in rodent population, vector is the flea
gallery of rickettsial vectors
Gallery of Rickettsial vectors

Rickettsia rickettsiae: tick

R. prowazekii: human louse

R. typhi: flea




  • Variola major and minor, large DNA virus
    • Mortality rate 20-60% for major, also blindness
    • Systemic infection, produced rash
  • In 20th Century, WHO conquered disease
    • No animal reservoirs, only human
    • Effective vaccine
    • Recognizable signs and symptoms
    • US vaccination discontinued in 1972
    • Declared gone in world in 1979
smallpox visuals
Smallpox visuals


  • Picornavirus
    • Small RNA virus
    • Enterovirus: spread by fecal-oral route
      • Attacks GI tract
  • In small percentage, attacks motor neurons
    • Leads to paralysis of different muscles, sometimes diaphragm
      • Children in iron lungs to help them breath
      • Lack of muscle function produces skeletal defects
polio continued
Polio continued
  • Epidemics peaked in mid 20th century
    • Salk and Sabin raced to produce vaccines
    • Hailed as heroes
  • On WHO’s list to eliminate