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Flashcards in Microbiology - 1 Deck (13):
1

What are the 7 major categories of organizms that cause infectious disease?

  1. Arthropods
  2. Bacteria
  3. Fungi
  4. Helminths
  5. Prions
  6. Protozoa
  7. Viruses

Notes:

  • identification & classification = essential for correct diagnosis, tx, and control!

2

Compare and contrast prokaryotes & eukaryotes

Bacteria = prokaryotes; All other = eukaryotes

Prokaryote:

  • No nucleus
  • Single circular DNA (chromosome)
  • Plasmids 
    • extrachromosomal DNA
  • Transcription & Translation = simultaneously
  • No membrane-bound organelles

Eukaryotes:

  • Nucleus (membrane bound)
  • Multiple chromosomes 
  • Transcription --> mRNA in nucleus
  • Translation --> ribosomes in cytoplasm
  • Membrane bound organelles

3

What are the advantages/disadvantages for intracellular & extracellular microbes?

Intracellular microbes (Microparasites - viruses, bacteria, protozoa, fungi)

  • viruses = obligate intracellular 
    • take genetic machinery from host 
    • take nutrients directly from intracell microenvironment
    • produce large # progeny
  • protected from:
    • host's immune defenses
    • antibiotics or other drugs
  • often live w/in immune cells
  • transmission btw host cells involves:
    • destruction; contribute to tissue damage

Extracellular microbes (Macroparasites - worms, arthropods):

  • take nutrients directly from
    • tissue fluids
    • feeding on host cells
    • intestinal contents
  • grow &reproduce freely
  • move & spread rapidly w/in body tissue
  • size --> problems to host's immune defenses
    • worms = several protective external layers & move quickly

4

What are the pros/cons of the human microbiota (normal flora)?

Pros:

  • normal flora PREVENTS colonization by potential pathogens
    1. skin bacteria
      • produce fatty acids --> discourage invasion
    2. gut bacteria 
      • antimicrobial activity + metabolic waste products --> prevent invasion  from other species
      • release organic acids --> metabolic value to host
      • produce B vitamins & vitamin K
    3. vaginal lactobacilli 
      • maintain acid environment --> supresses growth of other organisms
  • antigenic stimulation provided by intestinal flora --> ensures normal development of immune system

Cons:

  • spread into previously sterile parts of the body if intestine or skin = perforated
    • teeth extration
    • UTI
  • normal flora --> causes of hospital--acquired infection 
    • pts exposed to invasive tx
    • burn victims
  • overgrowth by potentially pathogenic members of the normal flore can occur, leading to:
    • composition of flora changes (ie after antibiotics)
    • local environment changes (ie increase in stomach or vaginal pH)
    • immune system becomes ineffective (ie AIDS/immunosuppression)
  • Potential pathogens take advantage of the opportunity to increase their population size / invade tissues

Notes:

  • In health, blood + blood fluids + tissues = sterile

5

What are the differences between the 3 types of symbiosis: commensalism, mutualism, and parasitism?

Commensalism: 

  • 1 species lives HARMLESSLY in/on the body of a larger species
    • smaller species makes use of environment to acquire nutrients
  • Majority of these are BACTERIA 
    • relationsip w/ host may be highly specialized 
    • ex: in humans, bacteria ferment and digest food
      • harmful if tissue damaged (surgery); flora changes (antibiotics); or immunity reduced

Mutualism

  • reciprocal BENEFITS for BOTH organisms 
    • relationship is OBLIGATORY for at least 1 member (sometimes both) 
  • Examples: 
    • BACTERIA & PROTOZOA living in stomach of domestic ruminants of cattle
      • digestion & utilization of cellulose  --> make fatty acids
      • host uses those as energy source

Parasitism: 

  • ALL pathogens are parasites!
    • 1 sided relationship --> benefits parasite ONLY!
  • Parasites establish innocuous assosciation in natural host, but may be pathogenic in others:
    • ie: rabies virus 
  • Example: 
    • Entamoeba histolytica - Protozoa in human that feeds on mucosa --> ulcers & dysentery

6

What is the evolution of parasitism?

Bacteria became parasitic by ACCIDENTAL CONTACT

  • 1st lived OUTSIDE host cell
    • evoluition of INTRACELL HABIT req further modification to allow survival WITHIN host cells
    • survival of microbe DEPENDED on ability to EVADE EUKARYOTE ERADICATION
  • May have evolved from symbiotically associated HETEROTROPHIC PURPLE BACTERIA

Evidence of endosymbiont origin of mitochondria: 

  • EUK cells still have endosymbiotic bacteria
  • Ribosomes of mitochondria = more like PROK 
  • Mitochondira have own DNA = circular 
    • control their own division
    • gene expression = similar to PROK
  • Production of energy associated w/ inner membrane or mitochondria
  • Antibiotics that kill bacteria, affect ribosomes of mitochondria

7

What are the 5 major ways microbes can enter the host?

  1. Skin
    • hair follicles
    • sebaceous glands 
      • skin bacteria can enter --> cause styes & boils
    • wounds/abrasions/burns
    • biting arthropods
      • penetrate skin via feeding 
    • Defenses
      • fatty acids inactivate microbes
      • pH ~5.5
      • normal flora
  2. Conjunctiva
    • specialized area of skin cleaned w/ tears & lids
    • contaminated w/ fingers/towels/flies
    • Defense:
      • antimicrobial tears
      • flushing of eyelids
  3. Respiratory Tract 
    • air contains suspended particles (smoke/dust/microorganisms) 
    • some microorganisms can overome cleansing mechnanisms
    • Defense
      • mucous has antimicrobial properties
      • alveolar macrophages remove foreign bodies
  4. GI Tract
    • some microorganisms can survive the intestine's defenses of acid, mucus, and enzymes
    • Defense
      • no particular cleansing mechanism besides flow (peristalsis)
      • saliva w/ antimicrobials 
      • mucous lined epithelial cells
      • digestive enzymes
      • secretory IgA
  5. Urogenital Tract
    • from perineum --> urethra
      • intestinal microbes
    • foreskin & fecal bacteria
    • Defense
      • low pH f ~5.0
      • bladder = protective mucous layer + secretion of Abs & immune cells
      • flushing action of urine
      • secretory IgA

8

What are the factors that can affect transmission of microbes?

Nearly all SHED from body surfaces

  • Extracted by vectors:
    • blood sucking arthropods 
      • transmit yellow fever, malaria, filarial worms 

Successful Transmission depends on: 

  1. # of microorganisms shed
  2. microorganisms stability in environment
  3. # of microorganisms needed to infect fresh host
    • efficiency of infection
  4. Genetic factors

 

9

What are the mechanisms for transmission between humans?

Microorganisms can be transmitted to humans via: 

  1. humans
    • most effective
  2. vertebrates
    • zoonoses
  3. biting arthropods

Most common infections spread by humans: 

  • skin
    • shed/direct contact
  • respiratory
    • droplets 
    • poor ventilation
    • air conditioning 
      • not readily controllable
  • fecal-oral
    • saliva
    • food/water
    • contaminated hands
      • controllable by public health 
  • venereal routes (urogenital tract) 
    • contact w/ discharge
    • mucosal contact w/ semen & vaginal secretions
    • perinatal
      • difficult to control b/c social factors

Note: 

  • Infections acquired from other species = not transmitted well from human --> human

 

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10

What are the mechanisms for transmission from animals to humans?

Transmission from Animals: 

  • domestic pets = reservoirs of infection
    • pathogens spread via: 
      • contact (bites, scractches)
        • rabies
      • vectors
        • ticks/sandflies
      • contamination w/ fecal material
        • hookworm/toxocarisis/plasmosis

Major infections transmitted this way: 

  1. TOXOCARIASIS = dogs
  2. TOXOPLAMOSIS = cats

 

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11

What is the difference btw surface and systemic infections?

Basics: 

Surface infection 

  • faiure to spread to deeper tissue
    • influenza virus in respiratory epithelium

Systemic Infection

  • invasion of deeper tissue
    • herpes simplex virus

Details:

  • microorganisms --> spread systemically b/c they FAIL TO SPREAD/MULTIPLE at the site of initial infection/body surface
    • next to no replication at site of entry 
      • measles/typhpoid
    • only after spreading thru body systemically --> large number of microorganisms delivered back to surface to multiply & shed
  • microorganisms --> spread systemically b/c they COMMIT THEMSELVES TO INFECTION BY 1 ROUTE
    • shedding/replication happens at another site
      • mumps/hep A = respiratory/mouth routes
        • invade & multiple in salivary glands & liver

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12

What are the mechanisms for the spread of infections through the
body?

Once microbe enters body via epithelium & basement membrane:

  1. tissue fluid has antimicrobial substances (Ab + complement)
  2. local macrophages (histocytes)
    • subcutaneous & submucosal
  3. physical barrer of local tissue structure
    • hydrated gel matrix
    • virus spread via step-wise invasion of cells
  4. lymphatic system
    1. infection can multiply locally or in lymph nodes
    2. evading phagocytosis --> reach bloodstream
  5. blood stream
    1. organisms free in blood = exposed to defenses such as Abs & phagocytes

Spread & replication affected by: 

  • genetics of host
  • genetics of microbe
  • other host factors: 
    • pregnancy
    • age
    • malnutrition
    • stress/hormones
    • pollution

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13

How can the genetic determinants of the host and the invading
microbe affect the spread of infection?

Genetics of the microbe & host determine spread & replication

  • Virulence = determined by: 
    • adhesion, penetration into cells, antiphagocytic activity, production of toxins, interaction w/ immune system
  • different microbial genes & gene produces are involved in diff stages of pathogenesis
    • some pathogens infect same species or related primate
      • measles, trachoma, typhoid, HBV, warts
    • some pathogens infect a wide range of hosts
      • rabies, anthrax
  • Genetic determinants of host --> susceptibility