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Wrap up path/micro > Pseudomonas/Gram - reading > Flashcards

Pseudomonas/Gram - reading Flashcards

1
Q

Pseudomonas aeruginosa: (aerobic, nonaerobic), (nonmotile, motile), (oxidase +, oxidase -) (Gram +, Gram -) (shape)

A

Pseudomonas aeruginosa is an aerobic, motile, oxidase +, Gram-negative rod that is slimmer and more pale staining than members of the Enterobacteriaceae.

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2
Q

Which gram - demonstrates the most consistent resistance to antibiotics of all the medically important bacteria?

A

P. aeruginosa

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3
Q

What would P. aeruginosa look like on gram stain?

A

Gram - rod…..

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4
Q

What is unique about a culture of P. aeruginosa?

A

Production of metallic blue, yellow, or rust-colored water-soluble pigments + fruity odor

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5
Q

Describe the growth conditions needed for P. aeruginosa.

A

Does not require enriched media for growth and can survive and multiply over a wide temperature range (20° to 42°C) in almost any environment, including one with a high salt content

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6
Q

How can one differentiate P. aeruginosa from the Enterobacteriaceae?

A
  1. P aeruginosa = oxidase +; Enterobacteriaceae = oxidase -
  2. Porin proteins of P. aeruginosa offer much less permeability (think Abx resistance)
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7
Q

Describe the different pigments produced by the Pseudomonas spp.

A

Pyocyanin = blue pigment = only by P aeruginosa

Fluorescin = yellow pigment that fluoresces under ultraviolet light = P aeruginosa + other free-living less pathogenic Pseudomonas spp

Pyocyanin and fluorescin combined produce a bright green color that diffuses throughout the medium

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8
Q

List 9 virulence factors of P. aeruginosa

A
  1. LPS
  2. Mucoid capsule
  3. Pili
  4. Flagellum
  5. Porins (impermeable to Abx)
  6. ExoA
  7. ExoS
  8. Elastase
  9. Type III secretion system (for ExoS)
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9
Q

What allows P. aeruginosa to be motile? What other function does this structure serve?

A

Single polar flagellum

Binding to host cells

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10
Q

How does P. aeruginosa produce its mucoid polysaccharide capsule?

A

Secretes alginate, a copolymer of mannuronic and glucuronic acids

Several enzymes pump carbs out into the alginate polymer

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11
Q

What “extra” virulence factor is present in P. aeruginosa colonies that you would expect to culture from a CF patient?

A

Mutations in regulatory genes which allow it to overproduce alginate

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12
Q

What is the function of P. aeruginosa ExoA toxin?

Which other bacteria produces a toxin with similar function?

A

Inhibits EF2 by ADP-ribosylation = shuts down translation of proteins = cell death

C. diphtheria (A chain)

(**remember: Cholera toxin & ETEC heat-labile toxin ADP-ribosylate AC Gs; Pertussis toxin ADP-ribosylates AC Gi)

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13
Q

What is the function of P. aeruginosa’s elastase?

A

Breaks down elastin, human IgA and IgG, complement components, and some collagens

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14
Q

What is the function of P. aeruginosa’s ExoS toxin?

A

Injected directly into host cells via a type III secretion system —> acts on G proteins affecting the cytoskeleton & signaling pathways and inducing apoptosis

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15
Q

List 3 common sites for P. aeruginosa infections

A
  1. Pulmonary
  2. Urinary
  3. Soft tissues
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16
Q

(T/F): Most patients with Pseudomonas aeruginosa infections are immunocompromised.

A

True

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17
Q

List 3 medical conditions leaving patients particularly susceptible to P. aeruginosa infections

A
  1. CF
  2. Leukemia
  3. Burns
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18
Q

Where is the primary habitat of P. aeruginosa?

A

Enviornment (soil, water, vegetation)

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19
Q

(T/F): If P. aeruginosa has been isolated from a patient, he/she must be immunocompromised

A

False - 2-10% of healthy individuals’ throats/feces are colonized with P. aeruginosa

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20
Q

List 5 ways in which P. aeruginosa opportunistically enters the body

A
  1. Burns
  2. Wounds
  3. Eyes/contact lenses
  4. Respiratory tract of CF patients
  5. UTI
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21
Q

List some common sources of P. aeruginosa infection

A

Humidifiers, medications, contact lens solutions, sink/faucet aerators, disinfectants

(Remember: P. aeruginosa can surive and proliferate in water with minimal nutrients)

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22
Q

(T/F): Healthy patients coming in contact with P. aeruginosa in contaminated food/drinking water accounts for a large proportion of infections.

A

False - think items susceptible to contamination (humidifiers, etc) + an immunocompromised patient

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23
Q

How long does the usual respiratory P. aeruginosa infection of a CF patient last?

A

Foeva/chronic

(Very hard to eradicate once a CF patient is infected)

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24
Q

(T/F): P. aeruginosa is the most common pathogen causing infection in CF patients.

A

True

(Leading cause of morbidity and eventual death of these patients)

25
Q

Which spp caused this finding?

A

Any Pseudomonas spp.

(Flourscein, produced by any of the Pseudomonas spp, is yellow under UV light)

26
Q

What must occur before P. aeruginosa can initiate infection?

A

Break in host defenses or a route past them (IT tube, contaminated solution)

27
Q

List the steps in P. aeruginosa pathogenesis

A
  1. Attachment
28
Q

What does P. aeruginosa use to adhere to host cells? What does it bind to on host cells?

A

Pili, flagellum, slime

N-acetylglucosamine or sialic acid receptors

29
Q

What property of immunocompromised cells lends to easier infection by P. aeruginosa?

A

Loss of surface fibronectin

30
Q

ExoA presence correlates with ___, while antibodies to ExoA correlate with ___

A

Fatality

Survival

31
Q

(T/F): ExoA can be detected in a P. aeruginosa-infected host immediately upon infection.

A

False - ExoA activated through quorom sensing

32
Q

What role does quorom sensing play in P. aeruginosa infections?

A

Once P. aeruginosa population reaches a certain threshold, signals turn on ExoA (and other factors’) translation and all cells release ExoA at once

33
Q

How would you know your patient infected with P. aeruginosa is expressing ExoA?

A

Activation correlates with invasive and locally destructive lesions

34
Q

What is the purpose of elastin and phospholipsa secreted by P. aeruginosa?

A

Acquire nutrients from host cells

35
Q

___ is found at sites preferentially attacked by P. aeruginosa

A

Elastin (lung and blood vessels)

36
Q

____ is the histological hallmark of P. aeruginosa infections

A

Hemorrhagic destruction

37
Q

(T/F): ExoS can be detected in a P. aeruginosa-infected host immediately upon infection.

A

True

38
Q

ExoS is associated with ___ and ___ within the host

A

Dissemination from burns and destruction of cells (esp. cytoskeleton)

39
Q

What is unique about the P. aeruginosa strains that infect CF patients?

A

Multiple mutations in regulatory genes that lead to overproduction of alginate

40
Q

List 3 factors unique to CF patients that aid in P. aeruginosa colonization

A
  1. Less highly sialylated cells (increased receptors for attachment)
  2. High osmolarity of secretions (facilitates expression of mutants)
  3. Defects in epithelial cells (less clearing by desquamation)
41
Q

What occurs once the bronchi of CF patients are invaded by P. aeruginosa?

A

Biofilm formation

42
Q

For which two functions is quorom sensing essential for P. aeruginosa?

A
  1. Turning on expression of alginate/toxins
  2. Biofilm production
43
Q

Which types of immunity are important in protecting hosts against P. aeruginosa?

A

Humoral and cell-mediated immunity

44
Q

Patients with defects in _____ immunity are particularly suscpetible to P. aeruginosa

A

Cell-mediated

45
Q

Describe the course of a respiratory infection with P. aeruginosa in a CF patient

A

Fluctuates between state of colonization and overt bronchitis or pneumonia

46
Q

What is shown here?

A

Lung at autopsy of CF patient showing inflammation/necrosis and biofilms of P. aeruginosa

47
Q

Which skin infections are caused by P. aeruginosa?

A

Hot tub folliculitis

Ecthyma gangrenosum

48
Q

What eye infections are caused by P. aeruginosa? Which is the most serious?

A

Conjunctivitis, keratitis, endophthalmitis

Keratitis - can progres to destroy cornea within 24-48 hours

49
Q

How is P. aeruginosa introduced into one’s eye?

A

Trauma or contaminated contact lens solution

50
Q

What ear infection does P. aeruginosa cause?

A

Otitis externa

(Inflammation of the outer ear and ear canal)

51
Q

Which P. aeruginosa virulence factor is primarily responsible for this finding?

A

ExoS

(Invasion and local destruction, especially of blood vessel walls)

52
Q

You suspect a patient has an infection with one of the Pseudomonas spp. How can you determine whether it is P. aeruginosa?

A
  1. Pyocyanin
  2. Ability to grow at 42°C
  3. Oxidase +
53
Q

Dx?

A

Ecthyma gangrenosum

(Due to bacteremia with P. aeruginosa, leading to direct invasion and destruction of blood vessel walls, manifested as cutaneous papules which progress into black necrotic ulcers)

54
Q

Which P. aeruginosa infection becomes particularly severe in diabetics?

A

Malignant otitis externa

55
Q

You determine that the causative agent is in fact not P. aeruginosa. List several other likely organisms.

A

Burkholderia, Moraxella, Plesiomonas, Acinetobacter, or Aeromonas

(Organism initially resembling Pseudomonas clinically usually turns out to be one of these)

56
Q

You culture an oxidase +, pigment-producing gram - bacillus from the urine of your patient with urinary frequency, dysuria, and retention. How would you treat?

A

Single agent

Third-generation ceph (ceftazidime, cefepime, cefoperazone)

Carbapenems (imipenem, meropenem)

Newer AMGs (gentamicin, tobramycin, amikacin)

Carbenicillin, ticarcillin

Cipro

57
Q

You culture an oxidase + gram - bacillus capable of growing at 42°C from a necrotic ulcer on a septic patient. How would you treat?

A

Multiple agents

Third-generation ceph (ceftazidime, cefepime, cefoperazone)

Carbapenems (imipenem, meropenem)

Newer AMGs (gentamicin, tobramycin, amikacin)

Carbenicillin, ticarcillin

Cipro

58
Q

What’s the issue with treating CF patients with P. aeruginosa infections?

A
  1. Reluctance to hospitalize these patients and efficacy of oral Abx is not well established
  2. Chronic infections = development of resistance
59
Q

Experimental P. aeruginosa vaccines could be potentially beneficial in which patients populations?

A

CF, burn, and immunosuppressed patients

Wrap up path/micro (2 decks)

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