Laboratory Identification of Fungi Flashcards
The diagnosis of fungal infections depends entirely on the
Selection and collection of an appropriate clinical specimen for microscopic analysis and culture
Many infections have a primary focus in what organ
Lungs
This specimen almost always included among the specimens selected for culture
Respiratory tract secretions
Dissemination to distant body sites may occur, and fungi may be recovered from nonrespiratory sites. True or false?
True
These steps are crucial for the recovery of fungi
Proper collection of specimens and rapid transport to the clinical laboratory
What happens to the viability of fungi over time?
Decrease
What to do when specimen processing will be delayed?
Specimens can be refrigerated for a short time
Specimens that cannot be refrigerated
Dermatologic specimens (skin, hair, nails), blood, and cerebrospinal fluid (CSF)
This are commonly are recovered on routine bacteriology media and fungal culture media
Yeasts
Respiratory tract secretions include
Sputum
Induced sputum
Bronchial washings
Bronchoalveolar lavage
Tracheal aspirations
The most common specimens collected for fungal culture
Respiratory tract secretions
How to ensure optimal recovery of fungi and prevent overgrowth by contaminants when using respiratory tract secretions?
Antibacterial antibiotics should be included in the battery of media used
Antifungal agent used when handling respiratory tract secretions
Cycloheximide
Function of cycloheximide when added to respiratory tract secretions
Prevents overgrowth by rapidly growing molds
How much specimen (respiratory tract secretions ) must be inoculated in each medium?
0.5mL
Cerebrospinal fluid collected for culture should be fil- tered through
0.45-μm membrane filter attached to a sterile syringe
CSF cultures should be examined for
Daily
What to do after CSF filtration is done?
After filtration, the filter is removed and placed on the surface of an appropriate culture medium with the inoculum side down. Alternatively, the specimen may be centrifuged and the concentrated sediment used to inoculate the culture medium
What should we do if CSF specimen is plated using a filter?
The filter should be moved to another location every other day
What should we do if less than 1 mL of CSF specimen is submitted for culture?
It should be centrifuged, and 1-drop aliquots of the sediment should be placed on several areas on the agar surface
Media used for the recovery of fungi from CSF should contain
No antibacterial or antifungal agents
Once submitted to the laboratory, CSF specimens should be processed
Promptly
If prompt processing of CSF is not possible, what should we do?
Specimen should be kept at room temperature or placed in a 30°C incubator
Why should CSF be kept at room temperature or placed in a 30°C incubator
Because most organisms continue to replicate in this environment
Automated blood culture systems
BACTEC
Bact/ALERT
VersaTREK
This has been proven optimal for the recovery of H. capsulatum and other filamentous fungi
Lysis-centrifugation system, the Isolator
How does lysis-centrifugation system works?
With this system, red blood cells and white blood cells, which may contain the microorganisms, are lysed, and centrifugation concentrates the organisms before culturing. The concentrate is inoculated onto the surface of appropriate culture media
When using lysis-centrifugation system, most fungi are detected within
First 4 days of incubation
Isolates of H. capsulatum may require approximately how many days for recovery
10 to 14 days
The optimal temperature for fungal blood cultures
30°C
The suggested incubation time for fungal blood cultures
21 days
Usually submitted for dermatophyte culture and are contaminated with bacteria or rapidly growing fungi or both
Hair, Skin, and Nail Scrapings
How to collect specimens for Dermatophytes?
Samples collected from lesions may be obtained by scraping the skin or nails with a scalpel blade or microscope slide; infected hairs are removed by plucking them with forceps
How to properly store Hair, Skin, and Nail Scrapings
These specimens should be placed in a sterile container; they should not be refrigerated
Media that is satisfactory for the recovery of dermatophytes
Mycosel agar, which contains chloramphenicol and cyclo- heximide
Dermatophytic cultures should be incubated for a minimum of _____ before being reported as negative
21 days at 30°C
Vaginal samples should be transported to the laboratory within
24 hours of collection
Why does vaginal swabs should be kept moist in sterile tubes?
This method of collection provides a specimen suitable for a wet preparation
Vaginal cultures should be screened for yeasts and incubated
30°C for 7 days
Urine samples collected for fungal culture should be processed
As soon after collection as possible
Does the 24-hour urine sample acceptable for culture?
No
How to ensure the recovery of fungi in urine specimen?
Media must contain antibacterial agent
Why does media containing antibacterial agents must be used to ensure the recovery of fungi in urine?
Because urine often is contaminated with gram negative bacteria
Tissue, Bone Marrow, and Sterile Body Fluids cultures should be incubated ar
30°C for 21 days
Bone marrow may be placed directly onto the surface of appropriate culture media and incubated at
30°C for 21 days
Sterile body fluids must be _____ before culturing
Concentrated by centrifugation
All specimens should be cultured as soon as possible to ensure the recovery of fungi. True or false
True
Specimens used to examine the presence of granules
Abscess fluid and Wound exudates
