ICL 2.17: Pseudomonas & Burkholderia Flashcards
What is the microbiology of pseudomonas aeruginosa?
Gram negative bacilli (rods) —> can be arranged in pairs
oxidase positive
What does pseudomonas aeruginosa ferment?
Lactose/glucose non-fermenting
Does NOT ferment lactose or glucose
Where is pseudomonas aeruginosa found in nature?
Sometimes present as a part of the normal flora of humans
It’s ubiquitous in nature; basically it’s found everywhere —> common in soil and water
Is pseudomonas aeruginosa motile?
Yes
Single polar flagellum
What conditions does pseudomonas aeruginosa need to grow?
Optimum temperature for growth is 37 C (body temperature) — but it can also grow up to 42 C
It also has very minimal nutritional requirements; it can even grow in distilled water
These two factors together make pseudomonas aeruginosa very hard to get rid of
Which disease is pseudomonas aeruginosa strongly associated with?
Cystic fibrosis!!
Nearly every CF patient will eventually acquire pseudomonas!
Once acquired, chronic infection will almost always ensue…
What is cystic fibrosis?
Autosomal recessive disease
Caused by mutation in CFTR channel which causes chloride ions to not be moved efficiently —> this leads to mucus building up outside of cells
Bacteria can then accumulate in the mucus and cause infections
This is especially important in airways
CXR looks like patchy infiltrates literally everywhere
How does pseudomonas aeruginosa cause chronic infections in CF patients?
Over 50% of CF patients have chronic pseudomonas aeruginosa infections by adolescence
It often mutates to better survive CF in the lung by expressing mucoid
Mucoid helps it to stick around in the lungs, literally
Infection causes chronic inflammation —> chronic inflammation causes lung damage —> lung damage causes death
What are the main virulence factors associated with pseudomonas aeruginosa?
- Alginate
2. Adhesins
What is the function of alginate in pseudomonas aeruginosa?
It’s a virulence factor that causes the mucoid phenotype!
It acts as an adhesin which lowers bacterial susceptibility to phagocytosis and antibiotic penetration
It promotes biofilm formation
Also called capsule, exopolysaccharide and glycocalix
What’s the function of adhesins in pseudomonas aeruginosa?
They are virulence factors that include fimbriae/pili and flagella
They provide adherence in the respiratory tract! Duh
Adhesins are aided by elastase, a protease that digests fibronectin to expose receptor
What are the toxins and secreted enzymes associated with pseudomonas aeruginosa?
- Exotoxin A
- Exoenzyme S
- LPS
- Pyoverdin
- Pyocyanin
- Alkaline protease
- Phospholipase C
What is the function of exotoxin A?
It’s a toxin of pseudomonas aeruginosa —> has necrotizing activity at infection site
It has identical function to the diphtheria toxin = ADP-ribosylates EF-2 which impairs translation
Even though it’s partially identical to DT, it’s antigenically distinct and uses a different receptor
What’s the function of exoenzyme S? In what patient population is it commonly seen?
It’s a toxin of pseudomonas aeruginosa
Specially, it’s an ADP-ribosylating toxin that is thought to impair phagocytosis
It’s frequently seen in infected burn victims
Does pseudomonas aeruginosa have LPS?
Yes because it’s gram (-) bacteria
It’s a toxin for pseudomonas aeruginosa
What is pyoverdin?
It’s a toxin of pseudomonas aeruginosa
It has a yellow pigment!!**
It binds host iron = siderophore
It also regulates secretion of other virulence factors
What is pyocyanin?
Toxin of pseudomonas aeruginosa
It’s blue in pigment**
It catalyze the production of superoxide and H2O2
It also stimulates release of IL-8 which attracts neutrophils
What’s the function of alkaline protease?
It’s a toxin of pseudomonas aeruginosa
It causes tissue destruction and interferes with host immune response
What is phospholipase C?
It’s a toxin of pseudomonas aeruginosa
It’s a hemolysis = lyses RBCs
It also facilitates tissue destruction
Does pseudomonas aeruginosa have antibiotic resistance?
Yes! It’s intrinsically resistant to antibiotics
Why is pseudomonas aeruginosa intrinsically resistant to a lot of antibiotics?
- Low permeability of its cell wall
- The genetic capacity to express a wide variety of resistance mechanisms
- It can become resistant through mutation in chromosomal genes which regulate resistance genes
- It can acquire additional resistance genes from other bacteria via plasmids, transposing and bacteriophages
- It can form biofilms
What are biofilms? Which bacteria are they associated with?
pseudomonas aeruginosa
Biofilms are communities of surface-associated microorganisms embedded in a matrix of extracellular polymeric substance (EPS) — think about the plaque on your teeth
Biofilms protect bacteria from the environment —> the concentration of antibiotics needed to kill bacteria in biofilms is several hundred times the amount needed to kill free-swimming bacteria
Biofilms are commonly associated with what?
Device-related infections like catheters, prosthesis, cardiac valves, etc.
You usually have to replace the indwelling device to get rid of the biofilm
what kind of pathogen is psuedomonas aeruginosa?
it’s an opportunistic pathogen
in healthy individuals infections are rare
what are the requirements for psuedomonas aeruginosa to cause an infection?
it’s an opportunistic pathogen; in healthy individuals infections are rare
colonization requires:
1. skin breakage/abrasions
- artificial inoculation (catheters, respirators)
- some type of immunodeficiency/immunosuppression or underlying condition
what tissues does psuedomonas aeruginosa infect?
it can infect almost any tissue because of its many virulence factors and high antibiotic resistance
what are the clinical diseases associated with psuedomonas aeruginosa?
- pulmonary infections
- skin and soft tissue infections
- eye infections
- ear infections
- UTI
- endocarditis
- bacteremia
how does psuedomonas aeruginosa cause pulmonary infections?
ranges in severity from asymptomatic colonization to sever necrotizing bronchopneumonia
typically seen in patients with cystic fibrosis, chronic lung diseases, congestive heart failure or neutropenia
immunocompromised patients are at higher risk, especially when previously treated with broad-spectrum antibiotics or when a mechanical ventilator is used
mortality rate is 70%
what types of skin and soft tissue infections does psudomonas aeruginosa cause ?
- burn infections
very common in patients with severe burns; incredibly difficult to treat
- folliculitis
typically from immersion in contaminated water (hot tubs)
- nail infections
- osteochondritis = inflammation of bone and cartilage
which patients get UTIs from psudomonas aeruginosa?
primarily in patients with indwelling catheters
it’s actually one of the leading causes of hospital-acquired UTIs
which populations are more likely to get psudomonas aeruginosa bacteremia?
people with with neutropenia, diabetes, extensive burns, hematologic malignancies, AIDS-related immunodeficiency
aka someone with an underlying immunodeficiency
how do you diagnose psudomonas aeruginosa ?
- pigmentation
P. aeruginosa produces two main types of soluble pigments: pyoverdin (yellow) and pyoctanin (blue)
- odor = grape-like odor
- culture
what would a psudomonas aeruginosa culture show?
gram (-) bacilli
B-hemolytic
oxidase positive
how do you treat psudomonas aeruginosa infection?
really difficult to treat due to intrinsic resistance and compromised host defenses of most patients
also it’s ubiquitous, so impossible to eradicate from the hospital environment
so a combination of antibiotics is generally used = B-lactam + aminoglycoside
choice of antibiotic depends on site of infection, severity, and local resistance patterns
how do you prevent psudomonas aeruginosa infection?
- maintain sterility of equipment especially ventilators, catheters
- avoid inappropriate administration of broad-spectrum antibiotics because they eliminates normal microbiota)
FLASHCARD: pseudomonas summary?
gram-negative rod, lactose non-fermenting, oxidase positive, motile
found ubiquitously in the environment
primarily an opportunistic pathogen of immunocompromised hosts –> major pathogen of the cystic fibrosis lung
produces a wide variety of virulence factors, including toxins, adhesins, and alginate
can be fairly easily identified due to the pigments it produces and its fruity, grapelike odor
is intrinsically resistant to many antibiotics and forms biofilms
causes a wide range of human disease—can infect almost any tissue given the opportunity
what is the pathogen?
the parents of Z., a 2-year old girl with a chronic cough, became alarmed because her cough worsened over a week’s time and her color “became poor” with coughing
her parents are unable to remember when she was last cough-free and state that she sometimes spit out yellow-green mucus after forceful coughing, most often when waking up in the morning
on examination, Z. was an alert but pasty and pale-looking child with increased respiratory effort and rapid breathing –> on inspiration, crackles were heard throughout the lung fields
her extremities showed moderate clubbing with mild cyanosis
CXR showed increased (abnormal) interstitial and peribronchial markings
throat culture was performed, a specimen of the green mucus was obtained and sent for Gram stain and culture –> sputum Gram stain showed many Gram-negative bacilli
based on the history, physical examination, and x-ray, a tentative diagnosis of cystic fibrosis was made
Pseudomonas aeruginosa
which pathogen is responsible?
58-year-old male was admitted to a hospital in southern India after suffering from high-grade fevers with intermittent cough and expectoration for the previous three months
his history included well-managed diabetes for the past 20 years, and no travel for the last 6 months
he had consulted 4 different hospitals previously and received several broad-spectrum antibiotics due to a diagnosis of P. aeruginosa infection at the last hospital visited
in spite of compliance with the antibiotic treatment, he remained febrile and his condition progressively worsened
CT of the thorax showed bilateral pleural effusions and left chest wall abscess
samples of pus, blood, urine, sputum, and pleural fluid were collected and cultured –> cultures of the pus, blood, and pleural fluid yielded pure growth of non-lactose fermenting colonies on MacConkey agar and non-hemolytic colonies on blood agar
microscopy showed gram-negative rods
burkholderia pseudomallei
what is MacConkey agar?
made of lactose
why is burkholderia pseudomallei often misdiagnosed?
it’s super similar to pseudomonas aeruginosa
so a delay in the identification of B. pseudomallei or a misidentification as another species (most commonly, Pseudomonas species or as a contaminant in culture) is not uncommon in laboratories that are unfamiliar with this organism
the problem is a delay in diagnosis can be fatal, since empirical antibiotic regimens used for suspected bacterial sepsis often do not provide adequate coverage for B. pseudomallei
what is the microbiology of burkholderia?
gram (-) bacilli (rod)
oxidase positive
very large genomes
is burkholderia anaerobic or aerobic?
obligate aerobes
what do burkholderia ferment?
lactose non-fermenting
does NOT ferment lactose
are burkholderia motile?
all species are motile except B. mallei which lacks flagella
what is commonly used to identify burkholderia?
they’re resistant to polymyxin B
which bukrholderia species are relevant to human health?
- B. cepacia complex
- B. mallei
- B. pseudomallei
what disease does B. cepacia complex cause?
causes the same range of diseases as P. aeruginosa
ex. respiratory disease, skin infections, endocarditis, etc.
similar to P. aeruginosa, are ubiquitous, can colonize moist surfaces and are opportunistic pathogens
what disease does B. mallei cause?
glanders
it’s an infection that usually occurs in equids via nasal secretion
humans can acquire it via aerosols
high mortality rate even with antibiotics because it’s really resistant
it has varying clinical symptoms and is really rare so it’s hard to diagnose
what disease does b. pseudomallei cause?
melioidosis
symptoms include:
- cough
- chest pain during breathing
- high fever
- headache and general muscle soreness.
- weight loss
but there’s varying clinical symptoms so it’s difficult to diagnose
where is B. cepaciae complex found in nature?
ubiquitous
can colonize moist surfaces and are opportunistic pathogens
it was originally identified as a plant pathogen that caused soft rot in onions
how difficult are B. cepacia to kill?
incredibly tough to kill
can survive betadine!! (the brown stuff they clean people with before surgery)
which diseases can B. cepacia complex cause?
commonly found in:
- CF patients
- chronic granulomatous disease
- UTIs (catheters)
- some patients who acquire B. cepacia infection develop the so-called “cepacia syndrome,” a rapidly fatal pneumonia and sepsis, with a high mortality
which bacterial infection is a contraindication for lung transplantation?
B. cepacia complex
which virulence factors are associated with B. cepacia complex?
- LPS (even more toxic than that of pseudomonas)
- lipase
- proteases
- flagella
- biofilms
which species is the only non-motile bukholderia species?
burkholderia mallei
what species does burkholderia mallei normally infect?
normally found in equids = horses, zebra, etc.
but it can also infect humans
during World War I, Germany initiated a clandestine program to infect horses and cattle owned by Allied armies with glanders
German agents infiltrated the United States and infected animals prior to their shipment across the Atlantic in support of Allied forces
why is burkholderia mallei a tier 1 select agent?
it would be a great bioweapon because:
- highly infectious through aerosol
- LD50 = less than 500 organisms
- no available vaccine
how are burkholderia pseudomallei infections usually acquired?
infection usually occurs via skin abrasion
it’s motile so it’s capable of polymerizing actin to spread from cell to cell
in what environment is burkholderia pseudomallei commonly found?
moist, tropical soils like rice patties
specifically south east asia
**Thailand
why is burkholderia pseudomallei classified as a tier 1 select agent?
- easily aerosolized
- LD50 < 10 organisms in the aerosol form (even less than B. mallei)
- high mortality rate despite antimicrobial treatment
- no vaccine
what is meliodosis?
caused by burkholderia pseudomallei
wide range of clinical manifestations; severity varies
melioidosis is able to affect any organ except heart valves
patients with meliodosis usually have risk factors for disease like diabetes, thalassemia, alcohol use or renal disease
frequently has a history of occupational or recreational exposure to mud of pooled surface water
what are the predisposing conditions for melioidosis?
- diabetes
- renal disease
- injury/drowning
how is B. pseudomallei transmitted?
- percutaneous inoculation
- inhalation
- ingestion
what are the similarities between burkholderia pseudomallei and B. mallei?
both are encapsulated and can live intracellularly in most cell types
no real transmission person-to-person
how are burkholderia pseudomallei and B. mallei related?
B. mallei is a “subclone” of B. pseudomallei
so B. mallei lacks ~20% of B. pseudomallei genes but has most virulence factors in common
so hopefully a vaccine against one will protect against both
how do you treat burkholderia pseudomallei infections?
all cases of melioidosis, even mild disease, should be treated with initial intensive therapy (at least two weeks of intravenous therapy) followed by eradication therapy orally for a minimum of three months
B. pseudomallei are characteristically resistant to penicillin, ampicillin, first- and second-generation cephalosporins, gentamicin, tobramycin, and streptomycin
FLASHCARD: Burkholderia
gram-negative, lactose non-fermenting, oxidase positive, obligate aerobes
3 species relevant to human health = B. cepacia complex (BCC), B. mallei, B. pseudomallei
BCC is a group of species not easily differentiated from each other, which cause a similar range of diseases as P. aeruginosa –> CF, CGD, UTIs, cepacia syndrome
B. mallei causes glanders, normally a disease of equids that can also infect humans –> hard to diagnose, high fatality rate; only non-motile burkholderia
B. pseudomallei causes meliodosis –> low infectious odse, high mortality, not easily identified; infection usually occurs via skin abrasion
those with diabetes and other underlying conditions are at higher risk; common in south/southeast Asia
what can you use to identify burkholderia?
resistant to polymyxin B
which burkholderia species are tier 1 select agents?
- B. mallei
2. B. pseudomallei
