L21 The Role of Microscopy in the Diagnosis of Infectious Disease Flashcards
Different ___ are used to cultivate bacteria. Growth depends on specimen type and/or the clinical disease.
Agars
What are the 4 major types of microscopy?
- Bright field (light)
- Dark field
- Fluorescence
- Electron microscopy
What microbes can be seen using light microscopy?
- Bacteria
- Fungi
- Parasites
What microbes can be seen using dark field microscopy?
- Spirochetes
What microbes can be seen using fluorescent microscopy?
- Bacteria
- Fungi
- Parasites
- Viruses
What microbes can be seen using electron microscopy?
- Viruses
2. Microsporidia
What color does a Gram positive bacteria stain? Gram negative?
Gram positive: purple
Gram negative: pink
In addition to bacteria, a Gram stain can help observe the presence of ___.
Inflammatory cells
Describe the steps of a Gram stain procedure.
- Plate the cells on a slide
- Primary stain - crystal violet
- Apply iodine to set the dye
- Decolorizer -alcohol/acetone (positive remains purple, negative becomes colorless)
- Counterstain - safranin (positive remains purple, negative becomes pink/red)
Why are Gram positive bacteria resistant to decolorization by alcohol/acetone?
They have a thick wall of peptidoglycan
What are the 4 clinical utilities of Gram stain?
- Direct examination of clinical material to make an initial diagnosis
- Determine the quality of the specimen
- Suggest an unusual organism or provide early presumptive bacterial identification
- Verify the clinical relevance of the culture
Streptococcus pneumoniae is a Gram ___ (+/-) ___ (shape).
Positive (purple); diplococci
Neisseria gonococcus is a Gram (+/-) ___ (shape).
Negative (pink);
diplococci
Neisseria meningitidis is a Gram (+/-) ___ (shape).
Negative (pink); cocci
What is a cryptococcus and how does it stain?
Fungi; purple-ish with a clear area (capsule) surrounding it
What type of bacteria is seen in normal vaginal secretions? Describe its stain and shape.
Lactobacilli; seen inside squamous cells; Gram positive (purple); rod
How will bacterial vaginosis differ from normal vaginal secretions on the molecular level?
The Gram positive bacilli are less present; there are multiple shapes of bacteria and more bacteria
How can you identify a respiratory specimen as poor quality?
Presence of lots of squamous cells
How can you identify a respiratory specimen as good quality?
Presence of ciliated columnar cells and/or neutrophils
Actinomyces are ___ (shape) and stain ___ on a Gram stain.
Filamentous; Gram positive (purple)
Campylobacter jejuni are Gram ___ (+/-) ___ (shape). What do they look like?
Negative (pink); rods; seagulls
Nocardia are Gram ___ (+/-) ___ (shape). What is unique about the appearance?
Positive (purple); filamentous with beading
Clostridium tetani are Gram ___ (+/-) ___ (shape). What do they look like?
Positive (purple); rod with round terminal spores; drumsticks
When do we do a blood culture?
When we are concerned that there is bacteria in the bloodstream (bacteremia)
How do we know if a bacterium that is normally found in the body is causing an infection or not?
Presence of inflammatory cells
What are acid fast stains used for?
To stain bacteria with cell walls containing long chain fatty acids
What qualifies as an acid fast bacilli?
Cells that resist decolorization after heat or detergent is used to drive the stain into the cell
What are the 4 types of microbes stained by acid fast?
- Mycobacteria
- Nocardia
- Cyrptosporidia
- Cyclospora
What are the 2 methods of acid fast staining and how are they different?
- Ziehl-Neelsen (uses heat)
2. Kinyoun (does not use heat)
What are the steps of the acid fast procedure?
- Plate cells on a slide
- Primary stain (carbalfuchsin red)
- Decolorizer (HCl, alcohol)
- Counterstain (methylene blue) –> acid fast stay red
What are the two types of silver stains?
- Warthin-Starry
2. Steiner
What type of tissue is needed for a silver stain?
Formalin fixed tissue
What are two examples of microbes that can be seen with a silver stain?
- Spirochetes like Treponema pallidum (syphillis)
2. Bartonella henselae (cat scratch disease)
What are 4 special stains used for fungi?
- Lactophenol cotton blue
- Gomori methenamine silver (GMS)
- Periodic acid-Schiff (PAS)
- Mucicarmine (mucin)
What can be seen using GMS?
- Yeast cells and hyphae
2. Pneumocystis jiroveci
What can be seen using PAS?
- Yeast cells and hyphae
What can be seen using mucicarmine?
- Cryptococcus capsule (the only thing that can be seen with this stain)
GMS stains fungi ___ (color).
Black
What is characteristic of aspergillus?
Hyphae with 45 degree angle branching and septae
PAS stains fungi ___ (color).
Pink
Mucin stain stains cryptococcus capsules ___ (color).
Very pink
What are the 4 types of stains for parasites?
- Wright Giemsa
- Wet mounts
- Trichrome
- Modified acid fast
Which parasite stain is used to examine a peripheral blood smear?
Wright Giemsa
What 3 microbes does Wright Giemsa help detect?
- Leishmania
- Trypanosomas
- Malaria
True or false - parasites are cultured in order to be studied.
False - they are not cultured; they are looked at under a microscope.
How does a fluorescence stain work?
Fluorophores or fluorochromes absorb energy from nonvisible UV and short visible wavelengths, become excited, and emit the energy in the form of longer visible wavelengths
What are the three types of fluorescent microscopy and what microbes do they identify?
- Auramine-rhodamine (mycobacteria)
- Calcofluor white stain (fungi)
- Flurescin conjugated antibodies (viruses, bordetella, legionella, pneumocystis)
___ in the cell wall of fungi will take up calcofluor.
Chitin
