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Clinical Microbiology > Opportunistic infection and Saprophytic fungi > Flashcards

Opportunistic infection and Saprophytic fungi Flashcards

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1
Q

Opportunistic mycoses (5)

A
  1. Yeast- Candidiasis
  2. Yeast- cryptococcosis
  3. Aspergillosis
  4. Zygomycosis
  5. Pneumocystis pneumonia
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2
Q

Candida species

A

Ascomycete yeast that is an opportunistic infection. They are normal microbiota of the skin and mucous membranes- the digestive and reproductive tracts of 40–80% of all healthy individuals harbor the yeast.

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3
Q

Candida morphology (3)

A
  1. Blastoconidia (conidia formed by budding)
  2. Pseudohyphae (chain of cells formed by budding). Constricted at septa (point of cell joining)
  3. True hyphae, NO constriction at septa
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4
Q

Cryptococcus species (4)

A

Neoformans, gattii and rare albidus, laurentii

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5
Q

Cryptococcus morphology

A

Blastoconidia, NO hyphae production- capsule associated with virulence

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6
Q

Cryptococcus

A

Not normal microbiota, causes asymptomatic pulmonary infection in healthy, severe progressive infection in immunocompromised. Causes
cryptococcal meningitis, cutaneous disease

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7
Q

Saprobic definition

A

Live on dead and decaying matter

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8
Q

Characteristics of saprophytic fungi

A

These fungi are saprobic and are opportunistic pathogens. They are normal flora of the skin and respiratory tract, and are also airborne (normally inhale conidia). Inhibited by cycloheximide. Repeated isolation of the pathogen is considered to be clinically significant. The fungi grow rapidly, within 1-5 days

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9
Q

Molds normally considered environmental contaminants (3)

A
  1. Zygomycetes (Phycomycetes)
  2. Hyaline molds
  3. Dematiaceous fungi
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10
Q

Class Zygomycetes (Phycomycetes)- 5 species

A

Sparsely septate, hyaline fungi. Includes lichtheimia (Absidia), Mucor, Rhizopus, Syncephalastrum, Cunninghamella

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11
Q

Hyaline molds

A

Septate, transparent hyphae. Includes Aspergillus fumigatus, Apergillus flavus, Aspergillus niger, Penicillium, Fusarium, Acremonium, Chrysosporium, Sepedonium

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12
Q

Dematiaceous fungi

A

Septate, dark colored hyphae. Includes Alternaria , Cladosporium, Aureobasidium, Curvularia, as well as Epicoccum, Drechslera, Nigrospora, Ulocladium, Bipolaris

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13
Q

Isolation of Zygomycetes from the environment

A

Found in decomposing organic matter such as fruit, bread, vegetables, seeds. Also identified in soil, compost piles, animal excreta. These infections are also hospital acquired from contaminated wound dressings

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14
Q

Zygomycetes epidemiology

A

These infections are acute, rapid, and difficult to treat. AIDS is not a significant risk factor, but Zygomycetes is common in other immunocompromised and diabetic individuals. There are very rare reports of infections in immunocompetent individuals, including allergic pulmonary disease- a hypersensitive response

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15
Q

Zygomycetes is a common infectious isolate in which populations?

A

Uncontrolled diabetes mellitus, ketoacidosis, other metabolic disorders, leukemia/lymphoma, neutropenia, long-term immunosuppressive therapy (transplant or autoimmune treatment). AIDS is not a significant risk factor

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16
Q

Colony features of Zygomycosis

A

Referred to as “lid lifters”- rapid growth, mature within 3-4 days. The colonies look like gray wool that will grow out of the plate. The colonies are susceptible to cycloheximide

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17
Q

Microscopic features of Zygomycosis

A

Has broad hyphae with few septations. The fungi forms rhizoids extending into the culture media. Above the media, it forms a stalk like structure called a sporangiophore, a sac called a sporangium, and forms asexual spores called sporangiospores

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18
Q

Rhizoids

A

Rootlike, hyphae extending into culture media, found in Zygomycosis

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19
Q

Sporangiophores

A

Found in Zygomycosis- specialized hyphal structure bearing a sporangium

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20
Q

Sporangium

A

Found in Zygomycosis- sac structure containing sporangiospores (asexual spores)

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21
Q

Zygomycosis Lichtheimia (Absidia)

A

Exhibit rhizoids, cause mycotic keratitis

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22
Q

Zygomycosis mucor

A

Do not have rhizoids, cause otomycosis. Morphology- broad, ribbonlike, coenocytic (nonseptate) hyphae found in tissue

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23
Q

Zygomycosis Rhizopus

A

Has rhizoids that are directly in line with sporangium. Causes otomycosis

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24
Q

Rhinocerebral zygomycosis

A

The infection begins in the paranasal sinus following inhalation of spores. The fungus spreads to the mouth and nose, producing macroscopic cottonlike growths. Mucor can subsequently invade blood vessels, where it produces fibrous clots, causes tissue death, and subsequently invades the brain. Symptoms- black necrotic lesions, necrotic lesions in the nasal mucosa. Patients can also exhibit purulent, black drainage from the eye orbit- can spread to brain. The most common clinical form is fatal within 1 week if not treated quickly- there is a 67% mortality rate

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25
Q

Who is most at risk for Rhinocerebral zygomycosis?

A

People in DKA, leukemia patients, and organ transplant recipients are high risk

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26
Q

Pulmonary zygomycosis

A

Follows inhalation of spores (as from moldy foods). The fungus kills lung tissue (necrosis), resulting in the formation of cavities in the lung. People can experience bronchitis, pneumonia, thrombosis, hemoptysis, and hematogenous spread of the infection. It is most commonly found in leukemia patients. Normally diagnosed upon autopsy or by fine needle aspiration cytology (FNAC). Difficult to distinguish from Aspergillosis. The infection can be fatal within 2 to 3 weeks and there is an 83% death rate

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27
Q

Gastrointestinal zygomycosis

A

Involves ulcers in the intestinal tract (stomach, colon, ileum). Symptoms- abdominal pain, peritonitis, intestinal perforation. Death from bowel infarction, sepsis, and hemorrhagic shock can result. This is a rare finding, but high risk populations includes malnourished infants or children, leukemia/lymphoma patients. Usually diagnosed upon autopsy

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28
Q

Cutaneous zygomycosis

A

Results from the introduction of fungi through the skin after trauma (such as burns, surgery, or needle punctures). Lesions range from pustules and ulcers to abscesses and dead patches of skin. Often does not develop into disseminated disease. The fatality rate is 16%

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29
Q

Disseminated zygomycosis

A

Follows any of the 4 types of zygomycosis. The most common site of infection is the brain, abscess formation and infarction can occur. The patient’s CSF examination appears normal. This type of Zygomycosis is most common in neutropenic patients with pulmonary infection. The fatality rate is 100%, it is diagnosed upon autopsy

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30
Q

Aspergillus species isolation from the environment

A

Found worldwide in the soil, water, food, or decomposing organic matter, and are wide-spread in the environment. They are common culture contaminants. The infectious inoculum is not clear, as healthy individuals are resistant to infection even when there is substantial exposure

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31
Q

Aspergillus species epidemiology

A

There are 184 species, 40 associated with human infection, 2 species predominate. Inhalation of conidia is the most common exposure. Invasive aspergillosis is a significant cause of morbidity and mortality, with invasive pulmonary Aspergillosis being the most serious form of infection. Disseminated disease fatality rate is 58 to 88%. Rapid identification of infection is vital for survival- species level identification influences treatment and outcomes

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32
Q

When are Aspergillosis isolates a concern?

A

Requires consideration of the patient’s medical history- some conditions put people at higher risk than others. When there are
large numbers of colonies on culture, it suggests infection

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33
Q

Aspergillosis risk factors (3)

A
  1. Bone marrow transplant
  2. Immunosuppressive therapies
  3. Leukemia/lymphoma, cancer patients receiving chemotherapy
34
Q

Types of Aspergillosis (7)

A
  1. Invasive pulmonary aspergillosis
  2. Hypersensitivity, asthma - allergic bronchopulmonary disease
  3. Tissue invasion
  4. Disseminated disease
  5. Ingestion of toxins from contaminated food
  6. Diseases without tissue invasion- otomycosis, abscesses
  7. Mycotic keratitis
35
Q

Acute invasive pulmonary aspergillosis

A

Most common Aspergillosis disease. The destruction of lung tissue causes significant respiratory impairment associated with fever, cough, and pain, may present as pneumonia. A “fungus ball” forms in the tissue- can result in an aspergilloma (granuloma), associated with other disease cavitation (TB, PCP, Histoplasmosis etc)

36
Q

Noninvasive aspergilloma

A

Ball-like masses of fungal hyphae that grow in the cavities of lung tissue formed as a result of a previous tuberculosis infection. Most cases are asymptomatic, though coughing and blood-tinged sputum may occur.

37
Q

Non-pulmonary Aspergillomas

A

Form in paranasal sinuses, ear canals, eyelids, the conjunctivas, brain, or eye sockets. These infections are more rare.

38
Q

Aspergillosis with tissue invasion

A

Found in the heart, CSF, bone, burn, mycetoma, sinuses

39
Q

Aspergillosis without tissue invasion

A

Can cause abscesses or otomycosis (in the ear). Otomycosis is often secondary to bacterial infections, following antimicrobial treatment. Can cause inflammation, scaling, partial deafness, or trauma to the ear.

40
Q

Which toxin can cause Aspergillosis if ingested?

A

Aflatoxin

41
Q

Systemic Aspergillosis

A

Rare, usually in AIDS patients, intravenous drug abusers or when introduced into the deep tissue through severe trauma. Around 20% of cases are stem cell transplant cases. Organs affected include the brain, GI tract, and kidneys, and the infection is acute. Organ failure and death can result. There is a 90% mortality rate

42
Q

Allergic bronchopulmonary disease

A

Can be caused by Aspergillosis- not an infection but an allergic disease. Patients can experience eosinophilia, asthma, IgE increase

43
Q

Mycotic keratitis

A

Infection of the cornea

44
Q

Colony features Aspergillosis

A

The colony is velvety to granular texture, dark-green to light green, and black. Some species are susceptible to cycloheximide. They grow rapidly, maturing within 3-4 days

45
Q

Foot cell

A

aspergillus- base of conidiophore where it merges with hyphae

46
Q

Conidiophore

A

aspergillus- stalk where conidia (asexual spores) are formed,

47
Q

Vesicle

A

aspergillus- enlarged structure at end of conidiophore, bears phialides

48
Q

Phialide

A

aspergillus- cell that produces and extrudes conidia, flask shaped

49
Q

Aspergillus morphology

A

Has septate hyphae. The conidiophore branches from the foot cell, and the vesicles and phialides branch from the conidiophore.

50
Q

Aspergillus fumigatus

A

Most common species (90% of the genus). They are also the most common species causing infection. The colonies are velvety and can be white or green. The reverse side is white to tan. Form single phialides and upper half of vesicle. The species grows at 45 degrees Celsius

51
Q

Aspergillus flavus

A

Associated with mycotoxicosis and produces potent aflatoxins. The colonies are velvety and can be yellow to green or brown. The reverse is gold to red brown. Single and double phialides, entire vesicle - point in all directions

52
Q

Aspergillus niger

A

Most common cause of otomycosis. The colonies are wooly, white to yellow then dark brown to black. The reverse can be white to yellow. Double phialides, cover entire vesicle -“radiate” head. Hyaline, septate

53
Q

Eurotiomycetes species

A
  1. Aspergillosis
  2. Penicilliosis
54
Q

Penicilliosis habitat

A

Ubiquitous in the environment- found in soil, decaying vegetation, compost, wood, dried foodstuffs, spices, dry cereals, fresh fruit and vegetables. They are also growing on building materials in water-damaged environments and are found in indoor air and house dust

55
Q

Penicilliosis epidemiology

A

200 species identified, no true human pathogens- many of the 200 species will not grow at 37 degrees Celsius. Only repeated isolation of fungus from tissue sections is diagnostic of significant infections
Risk factors: Immunocompromised host – Acute leukemia, AIDS

56
Q

Penicilliosis diseases (4)

A
  1. Pulmonary infection
  2. Keratitis
  3. Allergy and hypersensitivity pneumonitis
  4. Rarely found BUT case reports: Endocarditis and urinary tract infection
57
Q

Penicilliosis pulmonary infection

A

Causes bronchiectasis- airway damage that results in widening and damage of airways, scarring after infection. Mucus is no longer cleared leading to repeated infections

58
Q

Penicilliosis colony features

A

Rapid growth, mature within 4 days. Form septate hyphae. Colonies are greenish-blue with white edges

59
Q

Penicilliosis morphology

A

Branched or unbranched conidiophores – bears metula, which supports phialide. The phialides produces chains of conidia (asexual spores). The colonies resemble a skeleton hand or a paint brush

60
Q

Pneumocystis jirovecii

A

An ascomycete of the normal respiratory microbiota. 75% of people worldwide have been exposed to the fungus by the age of five. Found in the lungs reside without causing overt infection until the host’s immune system becomes debilitated.
In immunocompetent people, the infection is asymptomatic, and generally clearance of the fungus from the body is followed by lasting immunity. However, some individuals may become long-term asymptomatic carriers. Obligate parasite, cannot survive on its own

61
Q

Pneumocystis pneumonia

A

An interstitial pneumonitis with plasma cell infiltrates. Cysts are found in infected lung tissue and bronchoalveolar lavage, but it does not grow in culture. Before the AIDS epidemic, the disease Pneumocystis pneumonia was very rare observed only in malnourished, premature infants and debilitated elderly patients. Now, the disease is almost diagnostic for AIDS. Once the fungus enters the lungs of an AIDS patient, it multiplies rapidly, extensively colonizing the lungs. Widespread inflammation, fever, difficulty in breathing, and a nonproductive cough are characteristic. If left untreated, lung tissue destruction and death occurs. Extrapulmonary infections of the ear, eye, liver, and bone marrow can also be found in AIDS patients

62
Q

Pneumocystis species

A

Worldwide distribution- humans and animals, serology suggests most people have been exposed by age 3. It was originally classified as a protozoan, but later there was identification of sterols in cell membrane through nucleotide sequences and biochemistry. It is an opportunistic pathogen that mainly affects AIDS patients. Causes pneumonia- causative agents are P. jiroveci in humans, P. carinii in other animals

63
Q

Pneumocystis jirovecii life cycle

A
  1. Asexual phase- trophic form replicates by (#2 to #3) mitosis
  2. Sexual phase
64
Q

Sexual phase of Pneumocystis jirovecii (5)

A
  1. Haploid trophic forms conjugate and produce a zygote or sporocyte (#2 early cyst)
  2. Zygote undergoes meiosis and subsequent mitosis to produce eight haploid nuclei (#3 late phase cyst)
  3. Maturation occurs and the spores exhibit different shapes (spherical and elongate). It is postulated that elongation of the spores precedes release from the spore case.
  4. After release, the empty spore case usually collapses, but retains some residual cytoplasm. (form frequently visualized in histology as crushed ping pong balls)
  5. Trophic stage, where the organisms probably multiply by binary fission is also recognized to exist.
65
Q

Pneumocystis jirovecii infection signs

A

A patient will have a history of a chest x-ray with abnormal features. There are diffuse bilaterally web like extensions. Multiple ill defined small bright patches in the lung are suggestive of pneumocystis pneumonia. Fluid or histology demonstration of cysts or trophs in lower respiratory tract specimens. Stain fluid from lungs or from biopsies with calcofluor white, Giemsa, or GMS. The use of fluorescent antibody on samples taken from patients is more sensitive and provides a more specific diagnosis. Fungi stains black and looks like ping-pong balls

66
Q

Mycotic Keratitis

A

Opportunistic infection associated with trauma, steroid use, glaucoma, and transplant. Clinical presentation- white or cream colored infiltrate. Complications include ulceration, scarring, and blindness. Fusarium species are the most common cause, the fungi are hyaline septate or sparsely septate

67
Q

Diagnosis of Mycotic Keratitis

A

Corneal scraping, use direct mounts and culture

68
Q

When to work up mycotic keratitis fungi (2)

A
  1. Repeated isolation of large numbers from the same culture site suggests infection
  2. Make judgment taking into consideration patient’s medical history
69
Q

Fusarium species

A

The second most common saprophytic fungal pathogen (after Aspergillus). It is most commonly found in the US and is found in plants, soil, decomposing organic matter

70
Q

Fusarium species diseases (4)

A
  1. Eye infections
  2. Sinusitis, septic arthritis & nails
  3. Disseminated infection in neutropenic hosts
  4. Fusariosis in allogenic HSCT cases is 4.21 to 5/1000 in HLA matched and 20.19 cases/1000 in HLA mismatched. (Inhalation, ingestion, trauma)
71
Q

Fusarium species colony and microscopic features

A

Rapidly growing and takes 4 days to mature. Colonies are wooly, white with pink to lavender center. Septate hyphae and have single or branching conidiophores. Tapering phialides producing banana or canoe shaped macroconidia with 3 to 5 septations, OR small oval microconidia in clusters

72
Q

Opportunistic isolates similar to dimorphic pathogenic fungus isolates (3)

A
  1. Acremonium species
  2. Chrysosporium species
  3. Sepedonium species
73
Q

Acremonium species

A

Similar to Sporothrix. and growth occurs in 5 to 7 days. Common culture contaminants that are isolated from soil, plant debris, and rotting mushrooms. This fungus does not convert to a yeast at 37 degrees Celsius. Filamentous fungi, can be found as a common saprophyte contaminant but can also be a cause of keratitis

74
Q

Acremonium species infections (5)

A
  1. Mycetoma
  2. Nails
  3. Cornea – traumatic implantation
  4. Disseminated infection in VERY immunocompromised-entry from skin or lungs most common
  5. HAI in patient from surgical suite with contaminated HVAC
75
Q

Acremonium sp. mold phase

A

Occurs at 25-30 degrees. Forms a delicate, flower-like morphological arrangement. Septate hyphae with long unbranched tapering phialides. Conidia are oblong, in clusters of single or double celled, found at the tip of the phialides

76
Q

Sporothrix sp. mold phase

A

Occurs at 25-30 degrees. Forms a delicate, flower-like arrangement. Narrow, septate hyphae with slender tapering conidiophores swollen at terminal end bearing round to tear-shaped conidia. Conidia form rosette-like arrangements. Converts to a yeast at 37 degrees C

77
Q

Chrysosporium species

A

Common culture contaminants. Isolated from soil, plant debris, dung and birds. Causes skin infection of dogs and reptiles, and is associated with skin and nail infections. RARE report of disseminated infection in patient with chronic granulomatous disease (CGD), cerebral infection in HIV. Does not convert to a yeast at 37 degrees C. Similar to Blastomyces dermatitidis and Histoplasma capsulatum

78
Q

Chronic granulomatous disease (CGD)

A

A genetic disorder in which white blood cells called phagocytes are unable to kill certain types of bacteria and fungi. People with CGD are highly susceptible to frequent and sometimes life-threatening bacterial and fungal infections.

79
Q

Chrysosporium sp. mold phase

A

Occurs at 25-30 degrees. Slow grower- 6 days to full maturity. Single conidia on short conidiophores - “light bulbs” with arthroconidia sometime present. Can be confused with Blastomyces dermatitidis or Histoplasma capsulatum

80
Q

Blastomyces dermatitidis morphology

A

Short or long conidiophores, round to pear-shaped conidia, lollipop-like appearance. Converts to a yeast at 37 degrees C

81
Q

Histoplasma capsulatum morphology

A

Short branches that bear round to pear-shaped conidia, maybe spiny. Converts to a yeast at 37 degrees C

82
Q

Sepedonium species

A

Common culture contaminant that is isolated from soil and plant material, but is not known to cause disease. Similar to Histoplasma capsulatum. Large conidia (macroconidia) – single-celled, round, thick-walled and rough/knobby/spiny. DOES NOT make microconidia, which are found with H. capsulatum. Does not convert to a yeast at 37 degrees Celsius

Clinical Microbiology (19 decks)

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