Pseudomonas/Gram - reading Flashcards
Pseudomonas aeruginosa: (aerobic, nonaerobic), (nonmotile, motile), (oxidase +, oxidase -) (Gram +, Gram -) (shape)
Pseudomonas aeruginosa is an aerobic, motile, oxidase +, Gram-negative rod that is slimmer and more pale staining than members of the Enterobacteriaceae.
Which gram - demonstrates the most consistent resistance to antibiotics of all the medically important bacteria?
P. aeruginosa
What would P. aeruginosa look like on gram stain?
Gram - rod…..
What is unique about a culture of P. aeruginosa?
Production of metallic blue, yellow, or rust-colored water-soluble pigments + fruity odor
Describe the growth conditions needed for P. aeruginosa.
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
How can one differentiate P. aeruginosa from the Enterobacteriaceae?
- P aeruginosa = oxidase +; Enterobacteriaceae = oxidase -
- Porin proteins of P. aeruginosa offer much less permeability (think Abx resistance)
Describe the different pigments produced by the Pseudomonas spp.
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
List 9 virulence factors of P. aeruginosa
- LPS
- Mucoid capsule
- Pili
- Flagellum
- Porins (impermeable to Abx)
- ExoA
- ExoS
- Elastase
- Type III secretion system (for ExoS)
What allows P. aeruginosa to be motile? What other function does this structure serve?
Single polar flagellum
Binding to host cells
How does P. aeruginosa produce its mucoid polysaccharide capsule?
Secretes alginate, a copolymer of mannuronic and glucuronic acids
Several enzymes pump carbs out into the alginate polymer
What “extra” virulence factor is present in P. aeruginosa colonies that you would expect to culture from a CF patient?
Mutations in regulatory genes which allow it to overproduce alginate
What is the function of P. aeruginosa ExoA toxin?
Which other bacteria produces a toxin with similar function?
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)
What is the function of P. aeruginosa’s elastase?
Breaks down elastin, human IgA and IgG, complement components, and some collagens
What is the function of P. aeruginosa’s ExoS toxin?
Injected directly into host cells via a type III secretion system —> acts on G proteins affecting the cytoskeleton & signaling pathways and inducing apoptosis
List 3 common sites for P. aeruginosa infections
- Pulmonary
- Urinary
- Soft tissues
(T/F): Most patients with Pseudomonas aeruginosa infections are immunocompromised.
True
List 3 medical conditions leaving patients particularly susceptible to P. aeruginosa infections
- CF
- Leukemia
- Burns
Where is the primary habitat of P. aeruginosa?
Enviornment (soil, water, vegetation)
(T/F): If P. aeruginosa has been isolated from a patient, he/she must be immunocompromised
False - 2-10% of healthy individuals’ throats/feces are colonized with P. aeruginosa
List 5 ways in which P. aeruginosa opportunistically enters the body
- Burns
- Wounds
- Eyes/contact lenses
- Respiratory tract of CF patients
- UTI
List some common sources of P. aeruginosa infection
Humidifiers, medications, contact lens solutions, sink/faucet aerators, disinfectants
(Remember: P. aeruginosa can surive and proliferate in water with minimal nutrients)
(T/F): Healthy patients coming in contact with P. aeruginosa in contaminated food/drinking water accounts for a large proportion of infections.
False - think items susceptible to contamination (humidifiers, etc) + an immunocompromised patient
How long does the usual respiratory P. aeruginosa infection of a CF patient last?
Foeva/chronic
(Very hard to eradicate once a CF patient is infected)
(T/F): P. aeruginosa is the most common pathogen causing infection in CF patients.
True
(Leading cause of morbidity and eventual death of these patients)
Which spp caused this finding?
Any Pseudomonas spp.
(Flourscein, produced by any of the Pseudomonas spp, is yellow under UV light)
What must occur before P. aeruginosa can initiate infection?
Break in host defenses or a route past them (IT tube, contaminated solution)
List the steps in P. aeruginosa pathogenesis
- Attachment
What does P. aeruginosa use to adhere to host cells? What does it bind to on host cells?
Pili, flagellum, slime
N-acetylglucosamine or sialic acid receptors
What property of immunocompromised cells lends to easier infection by P. aeruginosa?
Loss of surface fibronectin
ExoA presence correlates with ___, while antibodies to ExoA correlate with ___
Fatality
Survival
(T/F): ExoA can be detected in a P. aeruginosa-infected host immediately upon infection.
False - ExoA activated through quorom sensing
What role does quorom sensing play in P. aeruginosa infections?
Once P. aeruginosa population reaches a certain threshold, signals turn on ExoA (and other factors’) translation and all cells release ExoA at once
How would you know your patient infected with P. aeruginosa is expressing ExoA?
Activation correlates with invasive and locally destructive lesions
What is the purpose of elastin and phospholipsa secreted by P. aeruginosa?
Acquire nutrients from host cells
___ is found at sites preferentially attacked by P. aeruginosa
Elastin (lung and blood vessels)
____ is the histological hallmark of P. aeruginosa infections
Hemorrhagic destruction
(T/F): ExoS can be detected in a P. aeruginosa-infected host immediately upon infection.
True
ExoS is associated with ___ and ___ within the host
Dissemination from burns and destruction of cells (esp. cytoskeleton)
What is unique about the P. aeruginosa strains that infect CF patients?
Multiple mutations in regulatory genes that lead to overproduction of alginate
List 3 factors unique to CF patients that aid in P. aeruginosa colonization
- Less highly sialylated cells (increased receptors for attachment)
- High osmolarity of secretions (facilitates expression of mutants)
- Defects in epithelial cells (less clearing by desquamation)
What occurs once the bronchi of CF patients are invaded by P. aeruginosa?
Biofilm formation
For which two functions is quorom sensing essential for P. aeruginosa?
- Turning on expression of alginate/toxins
- Biofilm production
Which types of immunity are important in protecting hosts against P. aeruginosa?
Humoral and cell-mediated immunity
Patients with defects in _____ immunity are particularly suscpetible to P. aeruginosa
Cell-mediated
Describe the course of a respiratory infection with P. aeruginosa in a CF patient
Fluctuates between state of colonization and overt bronchitis or pneumonia
What is shown here?
Lung at autopsy of CF patient showing inflammation/necrosis and biofilms of P. aeruginosa
Which skin infections are caused by P. aeruginosa?
Hot tub folliculitis
Ecthyma gangrenosum
What eye infections are caused by P. aeruginosa? Which is the most serious?
Conjunctivitis, keratitis, endophthalmitis
Keratitis - can progres to destroy cornea within 24-48 hours
How is P. aeruginosa introduced into one’s eye?
Trauma or contaminated contact lens solution
What ear infection does P. aeruginosa cause?
Otitis externa
(Inflammation of the outer ear and ear canal)
Which P. aeruginosa virulence factor is primarily responsible for this finding?
ExoS
(Invasion and local destruction, especially of blood vessel walls)
You suspect a patient has an infection with one of the Pseudomonas spp. How can you determine whether it is P. aeruginosa?
- Pyocyanin
- Ability to grow at 42°C
- Oxidase +
Dx?
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)
Which P. aeruginosa infection becomes particularly severe in diabetics?
Malignant otitis externa
You determine that the causative agent is in fact not P. aeruginosa. List several other likely organisms.
Burkholderia, Moraxella, Plesiomonas, Acinetobacter, or Aeromonas
(Organism initially resembling Pseudomonas clinically usually turns out to be one of these)
You culture an oxidase +, pigment-producing gram - bacillus from the urine of your patient with urinary frequency, dysuria, and retention. How would you treat?
Single agent
Third-generation ceph (ceftazidime, cefepime, cefoperazone)
Carbapenems (imipenem, meropenem)
Newer AMGs (gentamicin, tobramycin, amikacin)
Carbenicillin, ticarcillin
Cipro
You culture an oxidase + gram - bacillus capable of growing at 42°C from a necrotic ulcer on a septic patient. How would you treat?
Multiple agents
Third-generation ceph (ceftazidime, cefepime, cefoperazone)
Carbapenems (imipenem, meropenem)
Newer AMGs (gentamicin, tobramycin, amikacin)
Carbenicillin, ticarcillin
Cipro
What’s the issue with treating CF patients with P. aeruginosa infections?
- Reluctance to hospitalize these patients and efficacy of oral Abx is not well established
- Chronic infections = development of resistance
Experimental P. aeruginosa vaccines could be potentially beneficial in which patients populations?
CF, burn, and immunosuppressed patients
