Basic biology of pathogens Flashcards

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1
Q

In what environment will you find Blastomyces?

A

Moist soil

Decomposing wood + leaves

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2
Q

In what environment will you find Coccidioides?

A

Dust

Dry soil.

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3
Q

In what environment will you find Histoplasma?

A

Soil with bird/bat droppings

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4
Q

Where do body lice live?

A

In clothes

(They just come to your body to feed, then go back and hide in seams)

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5
Q

Describe the microscopic morphology of: Blastomyces

A

Mould phase: (25-30C)

  • Lollipops + double thick “broad based” buds.
  • Septate hyaline hyphae with unbranched short or long conidiophores @ 90degrees
  • “Lollipop” (round/pear) unicellular conidia at apex, emerging directly from the hyphae.

Yeast phase: (37C in tissue or on enriched agar)

  • Thick-walled.
  • Broad-based budding.
  • Often see pairs since buds remain attached until same size as parent cell.
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6
Q

Describe the microscopic morphology of: Coccidioides

A

Mould form: (in environment)

  • Septate, branched hyphae.
  • Thick-walled, barrel-shaped arthroconidia that alternate with empty (“disjunctor”) cells.

Yeast form: (in tissues/body fluids)

  • Large, round, thick-walled spherules which contain endospores
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7
Q

Describe the microscopic morphology of: Histoplasma

A

Mould form: (environment)

Young:

  • Septate hyphae bearing round/pear smooth microconidia on short branches or right on the sides of the hyphae.

Mature (after several weeks):

  • Large, thick-walled, round macroconidia: tuberculate, knobby, with short cylindrical projections.

Yeast form: (tissues, culture 35C)

  • Narrow-based budding yeast.
  • Thick/double wall appearance.
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8
Q

How many cells make up a single protozoan?

A

One

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9
Q

How does Blastomyces exposure lead to infection & disease?

A
  1. Spores (from mould form) are inhaled from damp soil with decomposing matter.
    (OR may be inoculated into the skin).
  2. Warmer temperature -> changes into yeast form.
  3. Yeast remains colonized in lungs.
  4. Yeast may disseminate in the bloodstream to other parts of the body.
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10
Q

How does Clostridium tetani cause disease?

A

Bacteria grow locally, releases tetanospasmin toxin

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11
Q

How does Coccidioides exposure lead to infection & disease?

A
  1. Spores (from the mould form) are inhaled.
  2. Temperature change -> change to spherules.
  3. Spherules divide (internally) until they are filled with endospores.
  4. Spherule ruptures ->
  5. releases endospores ->
  6. disseminate into the surrounding tissue.
  7. Endospores develop into new spherules + repeat this cycle.
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12
Q

What are the virulence factors for Enterococcus spp.?

A

Few:

  • adhesins
  • cytolysins
  • proteases
  • (antibiotic resistance)

But very susceptible to phagocytosis

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13
Q

Virulence factors of S. pyogenes?

A

M protein: a virulence determinant!

  • adherance to host cells
  • inhibits phagocytosis
  • antigenic, but mimics human tissues, so immune response can cross react with human tissues, causing rheumatic fever, rheumatic heart disease, glomerulonephritis.

Capsule:

  • inhibits phagocytosis
  • made from hyaluronic acid
  • indistinguishable from mammalian hyaluronic acid
  • a poor immunogen

Fimbriae/pili, Lipoteichoic acid, F protein :

  • for attachment to host cells
  • fibrils support M protein, other proteins
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14
Q

Virulence factors of Streptococcus agalactiae?

A

Capsule = major virulence factor

  • inhibits phagocytosis
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15
Q

How does Histoplasma exposure lead to infection & disease?

A
  1. Spores (from the mould form) are inhaled.
  2. Warmer temperature ->yeast form.
  3. Yeast are phagocytosed by immune cells
  4. ->regional LNs.
  5. Yeast survive inside the immune cells and travel in the blood to other parts of the body.
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16
Q

Describe the pathophysiology of LTBI activation ->active pulmonary TB disease

A
  • Granuloma bursts
  • Releases bacteria
  • Causes hemoptysis
  • Bacteria replicate further in the lungs.
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17
Q

What are the purposes of protozoan cysts?

A
  1. To protect them against a harsh/unstable environment (for days/weeks).
  2. For morphogenesis/nuclear division (i.e. the formation of their structures).
  3. For transmission to a new host
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18
Q

Which protozoa live in human blood/tissues?

A
  1. Plasmodium
  2. Leishmania
  3. Toxoplasma
  4. Babesia
  5. Trypanosoma
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19
Q

Which are the free-living protozoa?

A
  1. Acanthamoeba
  2. Balamuthia
  3. Naegleria
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20
Q

Which of these intestinal protozoa are pathogenic?

  • Entamoeba histolytica
  • Entamoeba dispar
  • Entamoeba coli
  • Entamoeba polecki
  • Endolimax nana
  • Iodamoeba buetschlii
  • Dientamoeba fragilis
A
  • Entamoeba histolytica
  • Dientamoeba fragilis
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21
Q

Which protozoa can live in/infect the human GI tract?

A
  1. Entamoeba
  2. Giardia
  3. Blastocystis
  4. Neobalantidium
  5. Microsporidians
  6. Coccidians
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22
Q

Which protozoa live in the human GU tract?

A
  1. Trichomonas
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23
Q

What are the virulence factors of S.pneumoniae?

A

Symptoms mainly from host’s immune response

Virulence factors mostly protect against immune response

  • Polysaccharide capsule:
    • prevents phagocytosis
  • secretory IgA protease
    • breaks down IgA, so no adhesion of bacteria to mucin
    • prevents muco-ciliary clearance
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24
Q

Describe the infection process of M.tuberculosis to the establishment of a latent infection.

A
  1. Transmitted through respiratory droplets –> inhaled into the URT.
  2. MTB phagocytosed by lung macrophages, but MTB blocks fusion with lysosomes.
  3. MTB persists + replicates within macrophages.
  4. Infected macrophages try to kill MTB by producing IFN-gamma (to kill intracellular pathogens), and recruit backup (other immune cells) to the area wit by releasing other cytokines.
  5. Incoming cells wall off the area by forming a large granuloma around the site of infection.
  6. Eventually, cells inside the granuloma die –>caseating lesion.
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25
Q

What are some virulence factors for VGS?

A

(very few)

No capsule (no Lancefield antigens)

  • Biofilms
    • adherance to endocardium, tooth enamel
    • resist immune defences, antibiotics
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26
Q

How is S. agalactiae prevented?

A
  • Screening mothers for colonization @ 35-37 weeks pregnancy
  • abx given to colonized moms & moms at risk (preterm birth, fever, previous GBS)
  • ensures protective levels of antibiotics in neonates
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27
Q

What are the member genera of the aerobic actinomycetes?

A

Suborder Corynebacterineae:

  • Nocardia
  • Gordonia
  • Rhodococcus
  • Tsukamurella
  • Dietzia
  • Williamsia
  • Segniliparus
  • (Corynebacterium & Mycobacterium are also in this suborder, but not consider aerobic actinomycetes)

Suborder Streptosporangineae:

  • Nocardiopsis
  • Actinomadura
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28
Q

What are the pathogenic species of Coccidioides and the differences between them?

A

C. immitis

  • California (San Joaquin Valley).

C. posadasii

  • More widespread.
  • Endemic throughout the Americas.
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29
Q

What are the pathogenic species of Histoplasma and the differences between them?

A
  • H. capsulatum* var. capsulatum
  • North + South America
  • H. capsulatum* var. duboisii
  • Africa
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30
Q

What are the three kinds of lice that infect humans?

A
  1. Pubic ~ (Pthirus pubis).
  2. Body ~ (Pediculus humanus corporis).
  3. Hair/head ~ (Pediculus humanus capitis)
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31
Q

What are the 5 asexual types of moulds?

A
  1. Hyaline
  2. Dematiaceous
  3. Dimorphic
  4. Mucormycetes
  5. Dermatophytes
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32
Q

Name 6 blood/tissue endoparasites:

A
  1. Naegleria
  2. Toxoplasma
  3. Trypanosoma
  4. Leishmania
  5. Plasmodium
  6. Babesia
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33
Q

What are the 3 mechanisms of motility for protozoa?

Give an example genus for each type.

A
  1. Pseudopods
    E.g. Entamoeba
  2. Flagella
    E.g. Giardia, Trichomonas
  3. Cilia
    E.g. Neobalantidium
34
Q

What are some reservoirs of Aeromonas hydrophila?

A

Fresh & salt water

35
Q

How is Aeromonas hydrophila transmitted?

A

Traumatic wounds in fresh water

36
Q

Reservoir of Bartonella henselae?

A

Cats mouths (commensal)

37
Q

How is Bartonella henselae transmitted?

A
  • Cat scratches,
  • bites,
  • feces contact
38
Q

What is the Babesia vector?

A

Tick

39
Q

How is Candida albicans transmitted?

A

Direct human-to human contact

40
Q

How is Entamoeba histolytica transmitted?

A
  • Fecal-oral
  • Oral-anal
41
Q

How is Francisella tularensis transmitted?

A

Animal and tick bites, scratches.

In Tasmania by possums

42
Q

Reservoir for S. pyogenes?

A

Upper Respiratory Tract

43
Q

How is S. pyogenes transmitted?

A
  • Respiratory droplets.
  • Skin
44
Q

Reservoir of S. agalactiae?

A
  • lower GI tract
  • GU tract

Commensal in 30% of healthy women of childbearing age

45
Q

How is Haemophilus influenzae transmitted?

A

Respiratory secretions

46
Q

How are Leishmania tropica, L. braziliensis, and L. donovani transmitted?

A
  • Bite of an infected female sandfly (Phlebotomus)
  • Direct contact with infected lesion
47
Q

How is Mycobacterium leprae transmitted?

A

Nasal secretions

48
Q

Reservoirs for Mycobacterium marinarum?

A

Fresh & salt water

49
Q

How is Mycobacterium marinarum transmitted?

A

Trauma in contaminated water, esp. cleaning aquariums

50
Q

Reservoirs of Mycobacterium ulcerans?

A
  • koalas
  • possums
51
Q

How is Malassezia furfur transmitted?

A

Direct/indirect contact with infected skin

52
Q

How are Wuchereria bancrofti & Brugia malayi transmitted?

A

Various Anopheles species (mosquitoes)

53
Q

How is Neisseria gonorrhoeae transmitted?

A

Sexually transmitted

54
Q

How is Neisseria meningitidis transmitted?

A

Respiratory secretions

55
Q

Reservoirs for Pasteurella multocida

A
  • dogs
  • cats
  • rabbits (normal mouth flora)
56
Q

How is Pasteurella multocida transmitted?

A

Bites or scratches

57
Q

What is the Plasmodium vector?

A

Female Anopheles mosquitoes.

58
Q

Reservoirs of Rickettsia & Orientia

A

wild animals (many)

59
Q

How are Rickettsia & Orientia transmitted?

A

Arthropods (ticks, mites, lice, fleas)

60
Q

Reservoir for Streptococcus pneumoniae?

A

Upper respiratory tract

61
Q

How is Sarcoptes scabiei transmitted?

A
  • Direct contact
  • Contact with infected clothing
  • Sexual contact
62
Q

How are Trypansoma brucei gambiense and T. brucei rhodesiense transmitted?

A

Both are spread by the tsetse fly

63
Q

How is Trypanosoma cruzi transmitted?

A

Reduviids, so called kissing bugs.

While biting, the bug defecates into the wound allowing transmission of T. cruzi.

Spread is aided by scratching the irritated site of the bite.

64
Q

How is Treponema pallidum transmitted?

A

Sexually transmitted

65
Q

How is M.tuberculosis transmitted?

A

Respiratory droplets (e.g. coughing, sneezing)

–>inhaled into the URT.

66
Q

What are the main Toxoplasma vectors?

A
  • Cats
  • Pigs
  • sheep
  • water
  • fruit
67
Q

Reservoirs of Vibrio vulnificus?

A

Salt water

68
Q

How is Vibrio vulnificus transmitted?

A

Exposure of wound to seawater

69
Q

Treatment of C.difficile?

A

discontinue implicated antibiotic

multiple abx courses required: spores not killed

Fecal transplant

70
Q

Treatment of Clostridium perfringens

A

rapid aggressive debridement

high dose penicillin

71
Q

Treatment of Clostridium tetani?

A
  • debridement
  • abx: only prevents growth, toxin still active
  • tetanus immunoglobulin
72
Q

How is Enterococcus spp. treated?

A

Combo therapy often,

e.g. gentamicin + a penicillin.

73
Q

How is S. pyogenes treated?

A

Penicillin

  • all strains susceptible

Erythromycin if allergic

Prompt treatment of pharyngitis avoids rheumatic fever etc.

74
Q

What is the best treatment for body louse infection?

A
  • Improve hygiene
  • Get rid of clothes (better than boiling/ironing)
75
Q

What is the best treatment for hair/head louse infection?

A
  • Shampoos with permethrin
  • Ivermectin
  • Mechanical removal with fine-toothed comb
76
Q

How is Streptococcus pneumoniae treated?

A

IV penicillins

  • (very effective in most cases)

Use cephalosporin if hypersensitive to penicillins

77
Q

What is the first-line treatment for active TB disease?

A

‘RIPE’:

  • Rifampin
  • Isoniazid
  • Pyrazinamide
  • Ethambutol
78
Q

What do the H.influenzae serotypes differ in?

How many are there?

Which are more predominant in North America? {}

A

Capsule polysaccharides

6 serotypes (a-f)

79
Q

What do the N.meningitidis serogroups differ in?

How many are there?

Which are more predominant here in North America?

A

Capsular types.

13 identified, 6 can cause epidemics (A, B, C, W, X, Y)

B > C > others in USA.

Increase in serogroup W in Canada since 2010 due to vaccine escape.

80
Q

How many S.pneumoniae serotypes exist?

A

~90 capsular serotypes (#s 1-48 w sub-types)

Vaccines cover the 13-23 most common

81
Q

What do the different S.pneumoniae serotypes reflect?

A

Capsular structure.

(No capsule = no disease.)

82
Q

What is the motile form of a protozoan called?

A

A trophozoite