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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