ICL 2.25: Francisella, Brucella & Acinetobacter Flashcards
what is the microbiology of actinobacter?
gram (-) coccus
aerobic
what is the microbiology of francisella?
gram (-) pleomorphic = coccobacilli
not motile
has a capsule
what is the micropbiology of brucella?
gram (-) pleomorphic = coccobacilli
not motile
strict aerobe
no capsule
what are the similarities between francisella and brucella?
- grow poorly in the lab = need 2+ days to see colonies
- non motile
- intracellular pathogens
what is the microbiology of francisells tularensis?
gram (-) coccobacillus
strict aerobic
non-motile
is francisella tularensis spore-forming?
no
but because of its capsule it can survive for months at low temperatures in water, moist soil, hay, straw, and decaying animal carcasses
how do you grow francisella tularensis?
chocolate agar
requires cysteine and blood for growth
takes 2+ days for colonies to grow
what are the virulence factors of francisella tularensis?
- capsule
- francisella pathogenicity island (FPI)
- LPS
how does the francisella tularensis capsule act as a virulence factor?
anti-phagocytic
binds complement = bacteria isn’t lysed
how does the francisella pathogenicity island act as a virulence factor?
it’s required for phagosome escape and possible secretion
how does francisella tularensis LPS act as a virulence factor?
its LPS has super long acyl chains and only has 4 acyl chains instead of 6
this modified LPS doesn’t stimulate TLR4 = immune evasion
so it’s not endotoxic = no cytokine-mediated inflammation and no TNFα
what kind of pathogen is francisella tularensis?
intracellular pathogen
which cells does francisella tularenis infect? what does it do?
it infects macrophages, dendritic cells, neutrophils, epithelial cells, etc. (basically everything)
it inhibits phagosome-lysosome fusion!!
then it somehow escapes the phagosome into the cytosol to replicate
it’ll eventually cause apoptosis of the cell so it can be released
what is francisella related to?
nothing…
Francisella are not related to any other genus
what are the francisella tularenis subspecies?
- F. tularensis subsp. tularensis = type A
**type A is the most virulent subspecies; LD50 = 10 bacteria!!
- F. tularensis subsp. holarctica = type B
where are F. tularensis type A and B found in the world?
type A = strictly north america
type B = North America, Europe, Russia, and Asia
where do most tularemia cases occur in the US?
- OK
- MO
- AR
- KS
how is F. tularensis transmitted?
ticks are the most common
but it can also be biting flies and mosquitoes
also aerosolizing an infected bunny/reservoir and breathing in the bacteria could cause it too or ingesting an infected bunny
no person-person spread
what time of the year is tularemia most common?
may, june, july = summer
what is the reservoir for F. tularensis?
- rabbits
- house cats
can also be ground squirrels, hares, muskrats, voles, mice, water rats, and other rodents are reservoir
F. tularensis has also been found in water, soil and vegetation
what are the possible disease states of F. tularensis?
- typhoidal
- pneumonic
- ulceroglandular
what is ulceroglandular F. tularensis?
you’ll get a cutaneous ulcer at the site of inoculation
you’ll also have proximal lymphadenopathy = super swollen lymph nodes
you can it from ticks or handling infected animals
mortality = 3%
what is pneumonic F. tularensis?
you’ll get atypical pneumonia or hilar lymphadenopathy
this is the most likely presentation of F. tularensis if exposed to aerosol
so you can get it from lawn mowing, haymaking, lab exposure or bioterrorism
mortality is 60%
what is typhoidal F. tularensis?
you can get septicemia and have systemic involvement
there will be no evidence of skin, mucosal or lymphatic involvement
this is what happens if the other F. tularensis presentations aren’t treated they can progress to typhoidal tularemia
mortality is 60%
what are the clinical symptoms of acute tularemia?
lasts 3-5 days
- Fever (up to 104∘F), chills
- Malaise
- Headache
- Sore throat
- Myalgia
- Anorexia
- Prostration
- Erythema nodosum
what are the clinical symptoms of prolonged tularemia?
lasts from day 6 to death
has all the symptoms seen in acute tularemia plus:
- cough (productive or non-productive)
- chest pain
- liver dysfunction
what is the pathology of an F. tularensis infection?
pathology mainly in lymph nodes, lungs, spleen, liver, and kidneys
there’s an influx of neutrophils, macrophages, and lymphocytes that may form granulomas
granulomas develop necrotic centers, sometimes caseating, typical of other granulomatous conditions
the infected macrophages can’t kill the bacteria so they undergo apoptosis –> francisella is released –> it infects new macrophages and travels through the lymphatics and infects other tissues and organs
how do you diagnose an F. tularensis infection?
- risk factors = rabbit hunting, ticks, sick cat
- microscopic examination of secretions, exudates, biopsy
but not very sensitive, francisella gram stains poorly and it’s hard to find sufficient organisms in specimens
- culture of ulcer scrapings, lymph node biopsy, or sputum = sensitive and specific but just use chocolate agar
- serology confirms diagnosis = compare titer with second titer 2 weeks later (4x)
how do you treat F. tularensis?
- doxycycline
- ciprofloxacin
F. tularensis produces B-lactamases, so B-lactams are ineffective
how do you prevent F. tularensis infections?
no vaccine
how do you grow brucella?
special Brucella medium
requires a week or more for visible growth on media
strict aerobe
which tissues does Brucella infect?
- epididymis
- placenta
- breast
- uterus
prefers to infect organs that are rich in erythritol because it metabolizes easier than glucose
infection causes sterility, abortions, or asymptomatic lifelong carriage
what kind of pathogen is brucella?
intracellular pathogen
replicates and persists within macrophages
prevents phagolysosome fusion –> persist/multiply within endosomal compartment
what are the virulence factors of brucella?
- urease
2. LPS
how does urease act a virulence factor for brucella?
buffers bacteria from low pH of stomach
urea –> CO2
what are the 2 types of LPS in brucella?
alterations in LPS O-antigen result in smooth or rough colony phenotypes –>- smooth isolates much more virulent than rough
rough colonies lack O-antigen (B. canis)
smooth = has O-antigen
rough = lacks O-antigen
either LPS form is much less stimulatory than LPS from other gram negatives
how does LPS act as a virulence factor for brucella?
has hella long acyl chains that are not recognized by TLR4
this LPS also inhibits apoptosis of infected macrophages
smooth LPS O-antigen groups block complement C3 binding
also the O-antigen amido groups are difficult to degrade so they block MHCII presentation of infected macrophages
what are the 4 brucella species that cause human disease?
- B. melitensis**
- B. abortus
- B. suis
- B. canis
where is brucellosis endemic?
Mediterranean Basin**
Middle East
Latin America
S.E. Europe
Asia
Africa
where is brucellosis common in the US?
Most U.S. cases in Texas and California
CA, TX, IL, FL = half of U.S. cases
how do you get brucellosis?
- abraded skin
- inhalation
- conjunctiva
- ingestion
no person-person spread
it’s shed in high numbers in milk, urine, birth products
**human disease is most often associated with consumption of contaminated unpasteurized dairy products (mainly milk and cheese)
what disease state does brucellosis cause?
causes sterility and abortions (pregnancy tolerance –> bacterial replication)
which groups are at risk for brucellosis?
- ingestion of unpasteurized milk, cheese, other dairy products
- slaughterhouse workers (reduced with brucellosis control measures in cattle)
- veterinarians (RB51 vaccine is B. abortus rough strain; rifampicin resistant)
- lab workers (highly infectious; BSL-3 required)
- hunters (feral swine, bison, elk)
what are the 3 forms of brucellosis?
- acute form
- undulant form
- chronic form
what is the acute form of brucellosis?
<8 weeks from illness onset
nonspecific “flu-like” symptoms include undulating fever, malodorous sweats, malaise, anorexia, headache, myalgia, and back pain
what is the undulant form of brucellosis?
<1 year from illness onset
- intermittent fevers, arthralgia, myalgia
- epididymo-orchitis in males
- spontaneous abortions in females
- neurologic symptoms may occur ≥ 5% of cases
what is the chronic form of brucellosis?
> 1 year from onset
symptoms may include chronic fatigue syndrome, depression, and arthritis
hepatomegaly, splenomegaly, lymphadenopathy
endocarditis in only 2% of cases but these can progress to death (80% of brucellosis endocarditis lethal)
what are the key symptoms of brucellosis in general?
- undulating fever
- malodorous perspiration
- arthralgia
how do you diagnose brucellosis?
- history!!!!
- culture from blood i gold standard
must use enriched blood agars to culture; takes 2 weeks to grow
- speciic antibodies are present in almost all brucellosis patients
IgM early 1st week then IgG
must see 4x increase in titer for diagnosis
what is the Ruiz-Castaneda test?
used to diagnose brucellosis
blood sample inoculated into vial containing both agar slant and broth media; must rotate vial daily to allow bacteria from broth to form colonies on agar
but takes 7-21 days to grow….
what is the lysis centrifugation test?
used to diagnose brucellosis
collect blood –> lyse RBCs in water and sodium citrate –> pellet bacteria –> plate
takes 2-4 days to grow; faster than Ruiz castaneda
how do you treat brucellosis?
because of slow growth, latency, and granuloma formation, need to treat with at least 2 antibiotics for 6 weeks
doxycycline and rifampicin
***except vets because the RB51 vaccine they give to animals is rifampicin resistant so you treat them with doxy and streptomycin
is there a brucellosis vaccine?
no
there’s a live attenuated vaccines for B. abortus and B. melitensis are used in animals but not in humans because they cause disease
where is actinobacter found in nature?
tolerate many environments; soil, skin, water, moist and dry surfaces
also part of normal flora of skin and oropharynx
common in hospitals (burn units, intensive care); easy to culture
which acinetobacter species is responsible for most human disease?
A. baumannii
it’s not a risk for immunocompotent people!
what diseases can A. baumannii cause?
- pneumonia
- septicemia
- wound infections
what are the risk factors to acinetobacter infections?
- combat injuries: present in 1/3 of cases from Iraq and Afghanistan**
- ventilator-associated pneumonia: 5 - 10% of long-term ICU patients
- Burn units and skin/soft tissue wounds: 2%
- UTIs: 1.6% catheter-associated
- diabetes
- chronic lung disease
how do you treat acinetobacter infections?
alot of acinetobacter is resistant to multiple antibiotics so first perform antimicrobial susceptibility testing
- broad-spectrum cephalosporin = ceftazidime or cefepime
- β-lactamase inhibitor (sulbactam) with β-lactam (ampicillin)**
- carbapenem = imipenem, meropenem, doripenem
- colistin**
is acinetobacter resistance a problem?
often resistant to multiple antibiotics
antibiotic resistance is rapidly spread via integrons, transposons, insertion elements
they’re resistant to B-lactams, aminoglycosides, quinolones, tetracyclines
FLASHCARD: micro, virulence factors, epidemiology, clinical, diagnosis, treatment of francisella tularensis
MICROBIOLOGY: Gram– coccobacilli but capsule may interfere; non-motile; requires cysteine and blood to culture; slow growing
VIRULENCE FACTORS: LPS is tetra-acylated, acyl chains 16-18 carbons long, monophosphorylated
EPIDEMIOLOGY: Type A (subsp. tularensis) > Type B (subsp. holarctica); ticks > rabbits > other animals; ~120 cases/yr; MO, AR, OK
CLINICAL: flu-like; ulceroglandular lesion may be present
DIAGNOSIS: Culture of ulcer, lymph node or sputum –> Agglut Ab; serology
TREATMENT: Doxycycline or cipro
FLASHCARD: micro, pathology, epidemiology, clinical, diagnosis, treatment of brucella
MICROBIOLOGY: very small Gram– coccobacilli; no capsule; flagella does not stimulate TLR5
PATHOLOGY: LPS acyl chains 28 carbons long, monophosphorylated , O-Ag blocks complement and MHC-II presentation
EPIDEMIOLOGY: B. melitensis»_space;> B. abortus > B. suis > B. canis; Mediterranean or unpasteurized cheese from C. America; Veterinarians
CLINICAL: Undulating fever, chills, malodorous sweats, arthralgia, malaise, anorexia, headache, myalgia, and back pain
DIAGNOSIS: Blood culture (two weeks) –> Agglut Ab; serology
TREATMENT: Doxycycline and rifampicin 6 weeks
FLASHCARD: microbiology, pathology, epidemiology, clinical, diagnosis, treatment of acinetobacter
MICROBIOLOGY: Gram– coccobacilli; form biofilms on medical instruments
PATHOLOGY/VIROLOGY: LPS potent inducer of inflammation
EPIDEMIOLOGY: Combat injuries Iraq and Afghanistan; ventilator-associated pneumonia; burn units
CLINICAL: pneumonia, septicemia, wound infections
DIAGNOSIS: Agar culture
TREATMENT: Sulbactam (small mol. B-lactamase inhibitor) with ampicillin; or colistin (polymixin E)
