Opportunistic Fungal & Filamentous Bacterial Infections Flashcards
What 3 filamentous bacteria cause indolent pneumonia in immunocompromised hosts and superficially resemble fungi in their slow clinical course?
Actinomyces
Nocardia
Rhodococcus (less important bc so rare)
What are the 2 most pertinent opportunistic yeasts? Fungi?
Yeasts:
- candida
- cryptococcus
Moulds:
- Aspergillus
- Zygomycetes
___________ is the most common cause of invasive mould infections in transplant and cancer patients..
____________ are classically associated with fungal sinusitis with brain invasion in patients with diabetes.
Aspergillus = most common in cancer/transplant
Zygomycetes = diabetes
Filamentous bacteria, like all bacteria are __________. They grow as thin ____________________ when in the exponential growth phase but revert to __________ single cells when in the plateau phase.
Prokaryotes that grow as thin branching filaments in the exp. growth phase, but revert to coccobacillary single cells in the plateau phase
What are the 3 main morphologies of fungi?
Give examples of each.
Yeast- cryptococcus, candida
Mould- aspergillus, zygomycetes
Dimorphic- histoplasma, blastomyces, coccidiodes
What are the 3 main drug options for fungi?
- Ergosterols- fungal cell membrane are inhibited by polyenes like amphotericin
- Azoles- inhibit fungal p450 14a demethylase that makes ergosterols
- eichinocandins- inhibit 1,3 B glucan synthase so targets cell wall of fungi
How can you differentiate growing bacterial filaments from fungal hyphae?
The fungal hyphae are thicker microscopically
Describe the most common actinomyces strain. Is it aerobic or anaerobic? Gram + or Gram - How does it grow? What differentiates them from nocardia?
Actinomyces israelii
- anaerobic/ aerotolerant
- G+ but stain irregularly
- branching filamentous rods
- different from nocardia because it does NOT have mycolic acid and is NOT weakly acid fast
Where is actinomyces found?
How does it cause disease in immunocompetent hosts?
In the normal oral flora and the female genital tract
- Trauma
- foreign bodies (like IUDs)
- injury/poor dentition
Why is actinomyces often mistaken for malignancy?
The infected tissue contains relatively few organisms and is a slowly growing mass of fibrous and inflammatory tissue that forms sinuses and fistulae
What are the 3 main syndromes associated with actinomyces?
- orocervicaofacial
- pulmonary disease
- abdominal/pelvic infections
____________ infection is the most common presentation of actinomyces. It is the result of _____________ and/or __________________.
Orocervicofacial infection is the result of:
- poor dental hygiene
- invasive dental procedures
A patient comes in to your office with a soft-tissue mass near the mouth that is painless, but shows fibrosis and scarring. He says he was at the dentists office last week getting a root canal.
What is the likely culprit of his infection?
His infection is likely to spread to _______ or _____ that drain from the original site of infection.
What are you likely to find on a stain of this?
Actinomyces- orocervicofacil infection
His infection spreads to sinus tract and fistula and you will see “sulfur granules”
A patient comes in with subacute chronic fever, chills, cough, night sweats and weight loss. You are suspicious of TB, but note that he has terrible dentition and extremely foul halitosis.
What should DEFINITELY be on the differential with TB?
Actinomyces
How does actinomyces appear on CXR.
Can be single lesion or multifocal
A distinguishing feature is that it does NOT respect anatomical boundaries so it can cross the pleura, lobes of the lung, extend through the thoracic wall, etc
A woman comes in complaining of abdominal pain, fever, night sweats and weight loss. When taking her history she tells you that she recently had an IUD put in. What is your #1 suspicion?
What are 2 other things that should be put on the differential?
What is treatment?
Actinomyces causing abdominal/pelvic syndrome
Consider:
Crohn’s
ulcerative colitis
Treatment is surgical resection of the infected tissue and a long course of antibiotics.
What are the 2 critical clues to the diagnosis of actinomyces on histopathological examination?
Is culture useful for diagnosis?
- sulfur granules (large ones are macroscopically visible in draining sinuses)
- masses of branching bacterial filaments surrounded by inflammatory debris
Culture would be diagnostic but it takes a minimum of 2 weeks (but often longer) for it to grow. When it does grow, however, it looks like a MOLAR TOOTH with aerial stalks
What is treatment for actinomyces?
- several weeks of IV PenG
- 6-12 months oral therapy of amoxicillin/clavulanic acid
Clindamycin&moxifloxacin in Pen allergic patients
Describe Nocardia.
- aerobic or anaerobic
- G+ or G-
- how does it grow?
- how is it differentiated from actinomyces?
- where is it typically found?
Aerobic
G+, weakly acid fast
It grows as branching filaments
It is differentiated from actinomyces because it has mycolic acid and stains weakly acid fast.
typically found in soil
What 2 major characteristics are similar between mycobacteria and nocardia?
- mycolic acid in the cell wall (mycobacteria is longer chained)
- trehalose dimycolate cord factor- allows for intracellular growth
How long does it take to grow Nocardia on a non-selective laboratory media?
How do the colonies appear?
It takes 5 days or more to grow
Colonies appear waxy and resemble fungal colonies in that they can form aerial hyphae
Which strain of Nocardia is most often associated with pulmonary disease?
With skin infections in countries in South/Central America?
Pulmonary- N. asteroides
Skin- N. brasiliensis
Where is nocardia usually found?
How do humans get infected?
Who is usually infected?
Where does the organism reside in the host?
It is found in soil and humans acquire it by inhalation.
They typically infect people lacking CMI (corticosteroids, immunosuppression, following transplant)
Nocardia lives within macrophages and prevents phagolysosomal fusion, prevents acidification and avoids killing by respiratory burst
What are the 3 main clinical syndromes associated with Nocardia?
- Sub-acute pneumonia
- Disseminated infection
- Cutaneous disease
A patient presents with cough and dyspnea that has been developing over several months. You treated them for multiple bacterial and fungal infections but they have not improved. What is the likely pathogen and what would you see on CXR?
Nocardia- multiple nodules that may cavitate
In nocardia disseminated infection, what does it typically manifest as?
They typically have pneumonia first and then it spreads to the brain.
- brain abscesses
- chronic meningitis
